DATAK PRINTED CIRCUITProcesses & Instructions

Contents:Comprehensive Instructions for Datak's

different processes for making PC boards.I ncluding a beginners introduction to PC

board making.

I ntroduction:Datak printed circuit board

making processes are intended for twouses: Making a prototype and for smallproduction runs. Users include designengineers, experimenters, as well asstudents and hobbyists. Instructors arei nvited to copy these materials freely.

There are a number of meth-ods for producing a printed circuitboard described herein. Read the fol-lowing synopsis to determine whichmethod best suites your projects. Mostli kely, you will eventually use more thanone of the following methods.

The METHODS:

The DIRECT ETCH method isusually the quickest way to produceone small circuit board. All beginnersshould try this method as it is a goodteacher. Not recommended when youneed to make many boards or for cir-cuits with numerous components.

Making Positive "artwork""Positive artwork" is needed for

any of these processes except DirectEtch. We suggest that you read thissection even if you will be using a com-puter to produce your positive.

Positive Presensitized PCBoard Method

This is an ideal method for making sev-eral PC boards (or more) and it is quickand accurate as well.

Comprehensive Datak Instructions for Printed Circuit Prototyping

(Positive Continued from column 1)

The method is fast and the mosttrouble free; getting excellent qualityis easy. It is somewhat higher in costthan other methods.

The positive method requiresthe purchase of boards that are pre-coated with sensitizer. Consequently,you will not have the freedom ofusing your own PC board stock.

I f you have an odd size or shapedboard , the negative method may bea better choice.

The Negative MethodThis method requires that

you spray a negative acting photoresist onto a blank PC board. It doesrequire several added steps (whencompared to the positive method).But, you have the freedom of coatingany type of PC board material andalso cutting and shaping the boardbefore spraying. AND, it is low incost.

Creating the NegativeTo make a board using the

Negative Method, you will need tomake a negative copy of your PCpositive board art. NegFast filmmakes it easy .... or use your com-

"Think Datak for your Printed Circuit Prototypes"

Why make a PC Board??This may sound like a strange

question, considering that we are pro-moting PC board making productshere. However, there are times whena PC board is not necessary and mayrequire a lot more time than you wantto spend.

A PC board will provide re-peated accuracy for any quantity ofthe same board, but if you are makingjust one, why not use a Protoboard in-stead?

DatakProtoboards are pre-etched with cop-per pads and holes spaced to accom-modated standard component leads. All,you need to do i s place your compo-nents, solder jumper wires i n place and'the circuit is done.

Datak offers several types ofProtoboard. The one above is specifi-cally designed for use with DIP IC's(catalog no. 12-607). The Protoboard'below is a general` purpose pattern withsimple copper donuts for lead wires.

................

i -a€€

..

..I°o ...........

o ..

......°a:;,This is universal board (catalog num-ber 12-602) with holes and donuts setup on 0.10" centers (as are numerousi ndustry standard components).

puter.

These and larger Protoboards are listed'Using Magazine Circuits

in the latest Philmore catalog;Lifting a circuit from a maga- they are not yet in the Datak

zine or book is described in this sec- catalogs.tion.

Before you use the solder-i ng iron....

"Breadboarding" a circuit is aterm from our grandfather's days.....when parts were fastened to awooden board to see how well a circuitwould perform. To provide a quickcheck to see if a given circuit wouldwork, parts were screwed or nailed toa board. Wires were twisted onto ter-minals, often never soldered.

Today we have SolderlessPrototype boards for testing circuiti deas. Parts are simply plugged intoone of these boards with no perma-nent connections, such as soldering.The circuit is powered up for testingand circuit changes are quick and

' easy.Solderless Prototype boards

have groups of holes spaced to acceptcomponent leads from IC's, resistorsand so on.

Below is a photo of a 7" wide proto-

board.

And here is a blown „up photo of the leftend of the board.Note the 8 pin DIPI C and resistor.Each pin of the IC isin a hole with a bussstrip that has fourother holes. You cani nsert componentsinto these holes or a22 gauge solid cop-per wire "jumper".

There are several sizes ofProtoboards, ranging from small andsimple to large with binding posts forpower and output (or whatever youwant to use them for). A serious ex-perimenter will need at least one board'as it can help you decide if a circuitneeds changes; or may not be worthbuilding at all. Check the Philmore(Datak s sister company) catalog fordetails. **

Comprehensive Datak Instructions for Printed Circuit Prototyping

Methods continued from page one.)

Etching the Board.Whichever method you use,

you will ultimately have to etch theboard as the last step before drilling,

l oading parts and soldering. Etching, ofcourse, is the chemical removal of cop-per except where your circuit is to be.Datak provides an excellent and eco-nomical product for this purpose. Theprocess is described near the end of

this booklet. **

Direct Etch, the quickest,cheapest method in detail.

What is a Dry-transfer? It is a sheet ofdecal patterns, in this case donut pads,on a carrier sheet. The backing sheetprotects the patterns during storage. Toplace a donut from this sheet, you simplyremove the backing, place the carriersheet where you want a donut and bur-nish with a blunt stick or pencil.

This section describes the useof Dry-transfers in the direct etch proc-ess. The Direct Etch method could beused for massive PC boards but wedon't recommend it. As a rule of thumb,anything larger than one or two IC'sand a transistor (with the usual list ofresistors, capacitors etc.) is probablytoo big. But you decide, after readingthe following and maybe trying a smallcircuit.

The Direct Etch method issimple: Directly on the board's cop-per surface, you mask the areas thatwill become your circuit; copper notprotected by masking will be re-moved during the etching process.

The making of a PC board could be de-scribed as removing copper from a PCboard "blank"; and leaving behind thecopper you will want. Before etchingthe board, you must protect the areasthat will become your circuit. DirectEtch is really just a simple, accuratemasking process.

"Think Datak for your Printed Circuit Prototypes"

2

One way to protect the cop-per would be to simply paint thepads for IC's and resistors etc. witha fine brush and some lacquer orvarnish. Actually this is not a badi dea for covering large areas tomake a ground plane; the varnishwould provide good protectionagainst the etchant. But what an im-possible chore for component pads,traces etc.!

This is where Datak prod-ucts for Direct Etch are a terrific

apart; and the pins on each side areon 0.10" centers. You can easilymatch this footprint by using anyDatak Dry Transfer donut pads on0.10" centers. Simply burnish ontothe copper the requisite number ofdonuts:

Like this>>

Rather thansearching throughthe Datak catalogto find the pat-terns that you willneed, consider

help. Patterns areavailable for just s 0 0

about any compo- a a Os O

nent's footprint. And O 0universal donuts will 0 0

work if there is not oa standard pattern.

DIRECT ETCH oYou will not need to 0measure; spacing 0 0 0between component ol eads (or contacts)will be matched by

1111 1111t

i llthe appropriateDatak Dry-Transfer

tillpattern. And, pre- Sudace Mount pattern

spaced donut pat-terns (there are

donuts

many sizes) can beused widely for"odd", or non-standard compo-nents.

an example:DIP ("dual

i nline package") U

I ntegrated Circuitshave two rows ofpins that are 0.30"

buying the Direct Etch Master Assortment(no. DE-973). Included are about any pat-

tern you can imagine includingsurface mount styles.

Resistors, capacitors, di-odes and other two-leadeddevices are easy; just bur-nish two donuts onto the cop-

per.About the only time that things get

a little tricky is when you have a part withno pattern. Then, measure the distancebetween pins and apply a donut for eachl ead, spaced appropriately.

(Direct Etch continued.)

Once you have burnished thecomponent patternsonto the bare cop-per, connect thepads either with dry_transfer lines in-cluded in the assort-ment, or use the EtchResist tape which comes in tiny rolls justlike miniature, black masking tape.

Etch Resist tape can be purchasei n various sizes. For starters, we suggesttwo widths,

the .031 "wide and .015"width.Always use the widest that will fit, it will beeasier to handle and a better conductor.With a finger, PRESS tape down firmly;etchant could etch under it when it is a -p ie

oose y.

Here is a small circuitwith pads connectedvia tape (shown 112size).

Comprehensive Datak Instructions for Printed Circuit Prototyping

finis

Resisttape >

When the pads andtraces have all beenapplied, you are ready to etch the boardas described in the etching section ofthis booklet. After etching, remove thepatterns and traces with a solvent such asacetone, toluene, or finger nail polish re-mover.

Direct Etch tips:1 Use a Printed Circuit Touch-up pen to

close gaps or even for traces. The pen's ink will re-sist etching if you get it on fairly heavily.IBy the way, positive artwork is created in the samefashion, except that you place the patterns on a clearfilm instead of directly on the copper.*Pay close attention to pin numbers; thiscan be tricky when components are on one side andthe copper (or, circuit) on the other.

1 When using leaded components, placethe components on the side of the board oppositethe copper. SMD components have to go on thesame side of the copper, of course.

MAKING POSITIVE ARTWORK"What is a positive?". The term positive does confuse

it is simple. A positive of a circuit is the artworkfor the circuit done in black on a clear film. Thepositive (or, positive art) will look like the pic-ture to your right. What you see in black willeventually be copper on the board.i mmediately below the positive is a negative ofthe same circuit.

When you use Datak Dry Transfers onclear film, you are creating a positive. OR, whenyou print a circuit from your computer's soft-ware (In most cases; some programs do havethe ability to print a negative if you specify it).

In order to make a PC board, whether youplan to use a positive or negative actingetch resist, you will need a positive to beginwith. The positive gives you the ability to makemany boards from the positive "master' and allwill be identical.

Computer software vs. drafting aids.There can be no question that the computer is thebest way to produce artwork in most cases. If you will be making a multi-l ayer board, a complex double sided board or simply a very large singlesided board, a computer i s the answer. If you also require a componentside silk screen plus a solder mask, the computer is the answer.HOWEVER, there is definitely a cost in getting started on a computer,which includes a l earning curve that may require many extra hours. If youonly want to do an occasional board, you may find the "old-fashion"paste-up method much easier.

If you are adept at producing a PClayout on a computer, skip the remainder of this section.

The circuit l ayout:

The simpte two-transistoramplifier becomes the layout

below.

3

"Think Datak for your Printed Circuit Prototypes"

people, but

A negative--

negative of a circuiti s flack backgroundon a transparent film;that is: the circuit i stransparent, clear film.

If you are creating your positive "fromscratch", you will first have to determine thelayout for the PC board. Having a clearschematic is one thing; converting thatschematic into a finished PC board is some-times quite a trick. You must determinewhere each component will be located andwhere each trace will be placed. This text isnot going to offer much help to you; circuitl ayout is such a variable that we must trustto your common sense with only the follow-i ng tips:;

1. Usually, the schematic suggests thePC board's layout; begin with about the

same order for major components.2. Try to stick with a single sided

board; its easier in many respects. It isbetter to add a few wire "jumpers" i n-stead of creating a two-sided PC board.

3. For seriously involved circuits(i.e. large and complex), consider morethan one PC board, linked with ribboncable or, jumpers between sections.

4. when you draw the layout,have' all components on hand and acaliper far measuring; specificationsheets for dimensions are helpful,

(continued)

(Making Positive Artwork continued.)

5. Draw the layout on graph paper before committing mate-rial to circuit art (see layout above). Where to start? Usually there isa "key" part; an IC or transistor or group of them, that should be thecenter of the board. After placing them, add the resistors and capaci-tors etc...

Once you have done your layout....Making the POSITIVE ARTWORK.

Comprehensive Datak Instructions for Printed Circuit Prototyping

Note that we are de-scribing making art fora circuit using compo-nents with lead wires,or pins.. That is be-cause surface mountis pretty straight for-ward ( pie) in com-parison. After youhave done this, youcan easily handleSMD (surface mount)

The Positive will be "built" on aclear piece of film (like Datak # MS21). Youbegin this process by placing a grid sheetunder the clear film. Then tape the two sothat they will not shift. The gird will be ayour guide, along with your layout. (Somecircuit builders do the layout on a gridsheet and place that under the clear film).Because components are made with leadson 1/10 inch spacing, the grid can help you

with accurate placement of donuts. So, Step- no. 1: Placea grid sheet on your drawing board and tape a clear sheeton top so that the two sheets will stay together. (Usequality masking tape so that it will also come off when fin-i shed.)

Step no. 2 is simply to place a donut pad whereverthere will be a component lead or pin. We suggest usingDatak dry transfers, if you place a pad in the wrong spot,just remove by scraping with your hobby knife. Accuratespacing for multi-pin devices such as IC's is accomplishedby both the pre-spaced Datak Donut padsand by following your grid. Together,they make the process very simple.

What size donut to use? You don'tneed to make that decision for transistors

and DIP's such as as IC's; just use the Datak pattern made for that part. Note the example; shown are patterns forTO-5, TO-18 and TO-92 transistors; all three leads are transferredtogether with proper spacing between leads..

But for 1/4 watt resistors and small capacitors, donut size foreach lead is mostly up to you. Fairly large donuts are easier to workwith but sometimes you may be forced to use very small pads due tospace limitations. In genera for two lead components, use a donutanywhere from .020" to .035" O.D.. You will soon get a feel for whichto use. For parts such as big electrolytics, use a donut with an insidediameter about the same as the components lead wire. Just be surenot to get so close to other pads that you will probably have a solderbridge by accident.

You can even get oval "donuts" (or pads) that'

o

40have a lead wire between them, which can be very

ohandy in tight places. The oval shape gives a smallpad . more area for the solder, producing a strong sol-der Joint in a small place. These donut pads are on1/10" centers, of course, so that they match the spac-i ng of standard IC's and other DIP (dual in-line pack-age) devices.

The column to your right depicts some helpful; tips. Takeyour time and shoot for accuracy, checking each trace twice Whenyou finish, you are ready to use presensitized positive boards or tomake a negative so that you can coat your own PC boards.

Transistor pads

4

Hole

Minimum0.020°

The hobby knife, or PCknife, is an indispensabletool that you'll need whenmaking a PC board using

any method.

"Think Datak for your Printed Circuit Prototypes"

Devices with two leads will bemounted in two donut pads.Spacing is your decision and youmay find it convenient to runtraces for other components underthe body of the part.

Pad size: Use a size thatwill surround the leadfairly closely. (Solder willbridge a considerable dif-ference in hole size andl ead diameter.) When youcan make it fit, select do-nuts that have a minimumof .020" between the holeand the O.D. (outside di-ameter).

I n general, try tomaintain at minimum 0.05"between pads; this re-duces solder bridges.(Although some patternsare much closer than this).Try for 0.040" minimumbetween traces.

ALWAYS lap tape ontop of pad to prevent

light leakage during theexposure process

(see sketches).

POLYESTER FILMPADS TAPE

Be sure to lap tape on top of pads.

to-Finish the artwork by connectinggether all pads that need to be connected.When you cannot make a connection betweentwo pads that must be connected because of in-terfering traces, consider using a jumper wire.(Or, could you reroute interfering traces?)Hopefully, most problems were solved duringthe layout process.

Once you have finished your PositiveArtwork, you can either use it with the presensi-tized, positive acting boards or you can create anegative for use with the Negative acting sensi-tizer. Both methods are described in detail inthis booklet.

Instructions for usingPOSITIVE, PRESENSITIZED PC BOARDS

ABOUT THE DARKROOM.

A darkroom is not needed for Datakprocesses; subdued incandescentroom lighting is generally good. Doeliminate sunlight from windows and,preferably, all fluorescent lights. Wesuggest either low wattage incandes-cent lights (25watts) at a distance ofseveral feet or yellow bug lights, stillkept at a distance. This wheneverhandling light sensitive productswhich includes Positive Boards, Neg-Fast film or when applying or han-dling boards that you have coatedwith Datak's negative resist.

if you already have a fullyequipped dark roam, there is cer-tainly no: harm in using it and noproblem with safe lights etc..

The WORKING AREAand equipment.It is important have a

good work area for the chemicalprocesses used to make PCboards. It is necessary both to besuccessful and for your personalsafety. You will need the followingfor certain:

A sink with both hot andcold running water; with a faucetthat will mix for warm as well. Thisshould be in an area that won'tmind some stains. The etchant, inparticular, can be messy andstains are likely.

You don't need a dark-room, but you will need to be ableto close out sunlight (see above ).

Ventilation is important,during etching and when using thenegative developer. In a confinedarea these chemicals may causethroat and eye irritation and evenlightheadedness even sicknesscould result. Providing an air flowshould prevent any reaction formost people; use a fan to exhaustfumes' via a window.

Goggles are a very goodidea when working with chemicals;and being close to a sink in casean eye; needs to be rinsed out.

ALWAYS keep the chemi-cals out of reach of youngchildren. Ingestion can be

very harmful or fatal.

POSITIVE PRESENSITIZED PC BOARDSThis is the easiest to use of the various methods, and is gener-

ally the most accurate. Although the negative method may cost you lessmoney, the time savings and fewer steps might compensate for materialcosts being a bit higher.

What are they? The boards are conventional, 1 oz. copper PCboards with a Fiberglas substrate. The copper is coated with a light sensi-tive chemical that is often called a resist or a sensitizer. When this coat-i ng is exposed to enough ultraviolet light, it will rinse away in thedeveloper solution, exposing the copper beneath. The copper is thenetched.

In brief, these are the steps we are about to describe in detail:

1. Expose the PC board with your positive artworkon top of it to UV light.

2. Develop the board in liquid developer.3. Etching the PC board will be covered in the sectionabout etching.

Before we start with the procedure, we need to advise you thatthere are two different types of positive board. They are very similar inmany respects, but you will want to be aware of the difference. TheStandard series has been around for many years. The catalog numbersfor the Standard series always begin with a "12" (e.g. 12-024 etc.).

The Premier series is a deluxe version and a newer innovation. Itcan be exposed with a photoflood, or even a standard incandescent 100watt light bulb, uses less developerand has a protective plastic, peel-offfilm that is a big plus. The resistcoating is also superior in that smalli mperfections have been reduced toalmost nonexistent (very rarely need-i ng touchup after developing). ThePremier series is somewhat morecostly (average 15-20%).Premierboards have part numbers beginningwith the numeral "14" (e.g. 14-024etc. )

The two biggest advantages in using the Premier series are thehigher quality coating and the plastic film protective cover. While thispeel-off cover is in place, you can measure, mark and cut the board tosize in normal room lighting, even bright lighting. Standard boards mustalways be handled in very subdued light.

Confusing Terminology.The industry tends to useseveral terms for "Positive-acting PC boards". A posi-tive board i s a positive boardand do not be distracted byvariations such as "positiveacting", "pre-sensitzed" orcoated etc.. And the termsPrecoated and Presensitzedare interchangeable as areresist and sensitizer.Technically, the coating is aresist and not a sensitizer,the resist is light sensitive.The term "positive" is thegiveaway

However, Standard boards should notbe considered to be terribly inferior; theyhave been the industry's mainstay fornearly two decades and can be countedupon for very good results. Here are themain differences

>Standard boards require UV light forexposure, Premier boards do not.

>Standard boards, mix developer withthree parts water vs. ten parts water forPremier boards.

>Standard boards should be checkedafter developing for possible touchup be-fore etching; they may need just a dabwith your PC ink pen.

(Continued next page)

Instructions for using POSITIVE, PRESENSITIZED PC BOARDS.

Your positive will be placedon top of the resist coatingon the copper side of thePC board during exposure.Be sure that the positive isnot upside-down; the cir-cuit in copper is going tobe oriented the same wayas your positive on top ofthe board.

Step 4. Exposethe board with yourpositive. Follow theExposure Chart forexposure time. Usean exposure frame.

Place your posi-tive on top of the sen-sitized coating on thePC board and sand-wich the two in theexposure frame.

The Exposure Frame: This device will be familiar to you if youhave ever made photographic prints. The frame is simply a holder for asmall board and piece of glass. With your positive in place on top of aprecoated board, put the two in the frame under the glass and slide intothe frame. The frame will hold the two tightly together for two reasons:(1.) the positive should never move around during exposure and (2.) thepositive is pressed tightly against the board so that light does not get un-der the positive. Now expose tolight.

The Light Source:See the chart at the bottomof this page. We are assumingthat your line voltage is be-tween 115 and 125 Volts AC.. if below this range, you mayhave problems. Also, for thesun, keep in mind that its ul-traviolet output could vary; es-pecially in large cities, on hazydays etc. .

Note that the Premierseries can use an ordinary 100watt white incandescent light bulb.Develop the board: While the board is being exposed, prepare a tray ofdeveloper solution. Mix the Datak developer concentrate 1:10 with waterfor the Premier series; or 1:3 for the Standard series. NOTE carefully;mix with very warm water. A cold developer is not going to work, itshould be above room temperature or warmer. (Be sure to use onlyDatak nos. 12-402 or 12-406.)

Use glass/plastic photographic tray.Use just enough developer to cover theboard. Rock the tray gently until the copperis fully exposed in areas to be etched. It willbe obvious to you when the copper is bare;be sure that there is no haze or film remain-ing. Rinse in cold water for a couple of min-utes. (Continued next page.)

The exposureframe; holds thepostive firmlyagainst the PCboard duringexposure to light

** l ook for desklamps that hold two bulbs *sun about noon to two P.M.

6

TINNIT©Tin Plating for PC boards.

Kit no. 12-800

This is a slick productthat should be of particular i nter-est to professional users. Whenyou get to the point where youhave a finished PC board, youmay want to tin plate the copperfor two or three reasons.

The tin plate, which sol-ders very easily, looks very sharp,shiny and clean. If you are mak-ing a board for a customer, tinlooks quite professional. And thelook lasts.

TINNIT will also provideprotection for boards that will bestored for later use; they will re-main solderable and the copperwill be protected.

I NSTRUCTIONSTINNIT is electroless, re-

quiring no electrodes or wires.

NOTE: WE RECOMMENDGOGGLES and RUBBER

GLOVES WHILE' WORKINGWITH THIS PRODUCT.

1. Dissolve the TINNITpowdered concentrate (markedno. ER-18) i n 12 ounces of verywarm water (temperature about130° F) and' then add water tomake one pint (16oz.).

NOTE: Use only a plasticor glass contaneror mixing anor storage.

o not use metalcontainers or caps With meta lliclinings.

2. Prepare the circuitboard for plating by removing alltraces of resist with either acetone, lacquer thinner orDATAKOAT® thinner. If oxidesare present, clean with scouringpowder rather than soap or deter-gent; do not use steel wool.

Continued on page seven)

BoardT type

F1 5 T 8-BLX2 bulbs**

app. noon

SUN*Datak ER-39

bulb

mix developer

concentratei 00 watt bulb

Premier onlSTANDARD R 12 to 14 min. 8 to 10 min. 12 to 15 min. 3 parts water to 1 not applicable

@ 7 inches any distance @12 min.PREMIER 9 to 12 min. 4 to 4.5 min. 10 min. 10 parts water to 1 10-12minutes

@7" 12" distance @12" distance.

Positive Boards continued ..... and Making a Negative from a Positive with Neg-Fast Film.

Etching: Your are now ready to etch the board; see the sec-tion on etching later in this booklet. After etching, you will be ready todrill the board and mount the parts, solder and finish the circuit.

Final notes: Here are some helpful tips for users of the posi-tive PC boards:

1. Store used developer in a plastic or glass bottle. Plastic isbest as you may squeeze most of the air out of the bottle and captightly. Do this because the developer will react, over time, with thecarbon dioxide in the air and decompose.

2. You can use the developer until it simply does not perform;then flush it down the sink with a fast cold water chaser. Storing de-veloper in a refrigerator can help to keep it fresh for very long periods.

3. We suggest leaving the resist on the board until after drill-ing. Remove the resist with solvents including acetone or a non-acetone fingernail polish remover. The later is available at most drugstores and discount stores.

4. IF the board proves to be tough to etch, you probably didnot develop it long enough and some resist residue remained behind.Or, said residue can also be caused by too short an exposure time,too weak a light source and so on.

Making a Negative from a positive or aMagazine page circuit.

Neg-Fast film is a product that will help youto easily create a negative for use with the NegativePhoto Resist Spray from Datak or any other negativeacting resist. Neg-Fast i s a plastic sheet, about asthick as a sheet of paper. It is available in small sheets5" X 6" or larger sheets 11" X 8". When exposed to light with yourpositive and then developed in a special liquid, a negative is produced.The process is simple and very reliable.

INSTRUCTIONS:Handle Neg-Fast film in very subdued lightand with no sunlight or fluorescent light pre-sent. It is also OK to use yellow light.

For use with a magazine arti-cle/circuit:

Step 1a. IF the circuit has no printingon the reverse side of the page , you can clipi t from the magazine. Or, you can use an of-fice photocopier and make a copy. Make a

a negative on the right.

good, high contrast copy with the circuitplenty dark, other areas white.Step 2a. A printed magazine clipping or pho-

tocopy such as this requires an exposure time of four minutes at adistance of 24" using the Datak no. ER-39 bulb. Except for this expo-sure time, follow the steps as given below.

For use with a pasted up or photographic Positive.(This is a positive circuit on a transparent film.)

Step 1. Use scissors or a sharp PC knife, cut the film to asize matching your circuit positive (or a bit larger).

Step 2. Place the film in an exposure frame with the emulsionside up*. the positive on top of the film (the positive can acei-ther direction, there is no "right-side-up".) Close frame securely.

(Continued next page)

A positive on the left,

000

(continued from page six.)Remove all cleanser residue bywashing thoroughly i n plenty of cleanwater: If you

o no thoroughly re-move all cleanser and etch residues,they can seriously deplete the TINNITbath.

3. Place the TINNIT solutioni n a Pyrex tray and heat to between120 and 140 degrees F. Immerse theboard for between 10 and 30 minutes.Agitate for a moment at five minutei ntervals. A bright tin plating will re-sult.

4. Rinse the board with run-ning tap water and_ dry with papertowels.

Special notes:If the TINNIT solution is left

standing it may evaporate, leaving - aprecipitate (white or li ght yellow).The precipitate will again dissolvewhen water i s added and heated andi s perfectly usable.

Do not leave, powder residueto heat on stove; heated dry salts candecompose and' release very irritatingsulfur dioxide and ammonia gases.

TINNIT may be stored forabout six months (longer if refriger-ated) in an airtight bottle made of ei-ther plastic or glass. Avoid metalbottle caps.

TINNIT WARNING: Thisproduct contains acidic tin salts.Although it contains no cyanides orother highly poisonous materials, it isa skin and eye irritant. In case of eyecontact, flush immediately with run-ning water. Consult a physician assoon as possible.

IF ingested, do not inducevomiting. Call a physician. Drinkplenty of water, as much as possible.

Never leave these chemicalsi n the reach of children. Youngerteenagers should be supervised by aknowledgeable and responsible adult.

Neg-Fast Film continued.

(continued from page seven)Step 3. Expose to the Datak ER-39 bulb at a distance of 24" for

1-1/2 minutes (4 minutes if a paper positive).Special note: For circuits larger than 4" X 4", you may find the outer

comers not fully exposed. For larger boards, you may suspend the ER-39 bulbso that it swings freely on its power cord. During a five minute exposure time,keep the bulb gently swinging randomly back and forth across the board whichis in its exposure frame about 24" directly below the bulb. Use a porcelainsocket as it can take the heat.

Step 4. Use only as much developer as needed; do not return useddeveloper to the bottle. Mix the developer concentrate with four parts of verywarm tap water. Place the developer in a shallow tray (either glass or plastic,not metal). Develop for about two minutes; or until you can see that you have agood clear image of the circuit's negative. The developer's temperature shouldbe warm, not less than about 72 degrees F but not above about 90 degrees.When fully developed, gently rinse in lukewarm tap water.

Step 5. Mix one part of the Fixer concentrate with 4 parts of warm tapwater and allow the negative to stand in this solution for about five minutes. (Ifyou are using the developer tray, be sure to rinse it out with water first.) It isnecessary to use only enough to cover the film but you may return unused fixerto the bottle. (When it comes to the time to buy new developers, throw awaythis old fixer as the developer package comes with new fixer too.)

Step 6. Rinse again in fresh, warm tap water and place gently betweena couple of paper towels to absorb excess moisture. You may then dry by leav-i ng it on top of another, fresh paper towel or hang it with a film clip. You mayuse warm air or heat to hurry the process, but do not exceed 122 degreesFahrenheit or you will distort the film.

Step 7. Touch up may be done with a black pen such as Datak nos.ER-15 or extra fine point ER-25. Eliminate anypin hole spots, if any.

Step 8. Finished. Use the negativewith a PC board coated with Datak no. ER-71sensitizer or with other maker's negative-acting PC boards.

Exhausted fixer and developer maybe flushed down the drain; follow up with a

couple of minutes of fast run-ning cold water. Use a shallow photo-

graphic tray (glass orplastic) for developing

and fixing ; use justenough developer orfixer to fully cover the

film.

`Identifying the emulsionside of the film.Each sheet of film willhave a notch along oneedge. Hold the sheet upin front of you; when the

notch is on the bottomedge and closest to your right hand, theemulsion side is facing you. OR, simply scratch each side with your PCknife tip. The emulsion side will scratch away revealing a clear film; thenon-emulsion side will not show scratches.

TIPS & MISCELLANYComputer Software ... if you areconsidering a computer program fordrafting your PC board layouts,PCDATAK may be a good choice.It is a DOS program but can rununder Windows or Wndows95. It isvery l ow cost, easy and quick tol earn and incredibly flexible for al ow cost program. To print circuits,you need to have a LaserJet printerwith the Postscript feature. Or, takethe circuit on diskette to Kinko's asthey have such printers. Datak'scatalog number for the software is12-077.

Soldering ... PC circuit layout de-scriptions in this booklet are as-suming that you will be handsoldering your final circuit board. Ifyour prototype will eventually be aproduction item and you are plan-ning to use dip or wave solderingequipment, then circuit layoutneeds to be done accordingly. Thisbooklet does not go into enoughdepth' to teach techniques for trueproduction boards.

For production, use asoftware to do your layout. Mostprograms incorporate acceptedtechniques that will keep you out oftrouble. Datak's software,PCDATAK no. 12-077 automaticallyprovides correct spacing betweentraces, donuts etc..

Drilling the PC board ... drilling witha standard, household hand drillcan be an excruciating chore; andit is very difficult to do a decent job.We suggest that you use only adrill press, even if you have to bega neighbor to use his. If you use ahi-speed mini-drill such as thosefrom Dremel, use a light dimmer toslow it down about 40%. (You willget a feel for the right speed afterusing it for a short time.) A slowed-down Dremel with a Dremel drillpress' is the ideal way to drill yourboards.

Small bits are availablefrom Datak and also from most in-dustrial supply houses which willcarry dozens of sizes.

The Negative Acting Photo Resist method

NEGATIVE PHOTO RESISTfor PC BOARD MAKING

The method is based upon using the Datak no. ER-71 PhotoResist liquid, which is a light sensitive spray-on resist. The small, 4 ouncebottle will cover about 1,700 square inches and is applied with the pumpaction sprayer included in the package. Good results can be expected ifyou carefully follow the steps.

You will need to begin with a quality negative. If you havea positive, see the section on using NegFast film to produce a negative.Or, use standard photographic process to make a high contrast negative.

Step 1. Clean the PC board. This is a critical step and must bedone well. Scour the board with water and a common kitchen cleanser(containing bleach) and very fine steel wool. Scrub the board and rinseuntil water sheets out evenly over the entire surface when you hold theboard horizontally under a pencil-leadstream of water. If the water tends topull away from the boards edges orany point on the aboard, clean itagain. If the board cannot pass thiswater test, it is "dirty" and must becleaned until it passes.

Dry the cleaned board withpaper towels. You could wipe with am-monia (never with alcohol). Handle bythe edges, don't touch the surface.

Step 2. Coat the Board with Resist. Do in subdued light* Theboard should be warm, ideally about 120 degrees F. Heat the board on ahot plate or you could warm it with a heat gun or hair dryer.

Lay the board flat and spray a light, continuousfilm . (Sink marks will indicate poor boardcleaning.) Sight along the board surface towardyour light; make the coat as even as possible.

Drying the board ina dark cupboardworks fine if there isplenty of volume inthe cupboard. But ifthe volume is quitesmall, there issometimes notenough air to absorbthe fumes and theboard takes a veryl ong time to dry.Don't expect a smalldrawer to dry two orthree boards over-night.

Step 4. Exposing the PC Board. Place yournegative on top of the resist coating and placethe two in a contact exposure frame. The framewill hold the negative and board tightly togetherto prevent light from leaking between them.

Expose the board to light using one ofthe following choices:

Spray a thin, evencoat. Thick coatsmay causeprobl

Step 3. Drying the PC Board. The boardmay simply be place in a dark cupboard to dryover night. Or, bake it in an oven at 140 degrees F for twenty minutes; the oven must bedark. Allow the board to cool ten minutes be-fore use.

I f your coating is not a clean looking,even coat with few signs of bubbles, considerrepeating the proc-ess by adding a sec-ond coat. Strive for athin coat, and aseven as you can

make it.

The exposure frameclamps the positive or

negative tightly against thePC board; and the glasstop allows exposure to

light.

* subdued light. After you clean the board and until you finish the develop-ing stage, work only in subdued lighting such as a 25 watt bulb severalfeet away or a yellow "bug" light bulb.

Sometimes steel wool willcontain oil; but it can be re-moved with some soap andrunning water. Soap,squeeze and rinse a pad twoor three cycles and it will beclean enough to use. A liquiddish soap is suggested.

Spraying the board is animportant step; try to get athin and even coat. A thickcoat can result in raggededges on pads and traces inyour finished board.tip: Pump the spray fully, donot try to squirt a light coatby pumping with shortstrokes. Start spraying offthe edge of the board andsweep across the board;each pump cycle should bea full stroke. (Short strokestend to shoot globs, whichare not good.)

Always spray on awarm board; a board that iscool is very tough to coatproperly. Some users let theboard dry and apply a sec-ond coating.

The negative is clear (trans-parent) where there will be cir-cuit and the "background" isopaque.

You can make anegative usingDatak Neg-Fastfilm or photo-graphically. Also,some softwarewill make anegative of a PCboard layout.

Developingtrays shouldbe largeenough thatthe PC board

Ragged edges on the resistimage mean that the resistwas not completely dry be-fore the exposure, OR, thatthe resist was applied too

heavily and should not havebeen such a thick coating.

Spread-out lines occur if youexposed too long or If thenegative was not in perfectcontact with the PC board.

This can happen if you use awarped board. If the patternis bad, you may as well sal-vage the board by cleaningoff the resist with lacquer

thinner and clean-I ng/recoating. (A warped

board can usually be gentlybent into shape.)

The Datak ER-8 Developercontains aromatic, partially

chlorinated hydrocarbons. Theproduct can attack plastics

and may discolor vinyl countertops, attack wood finishes andso on. In addition to the pre-cautions listed on the pack-age, don't use this product inareas that can't stand some

abuse.Never leave such chemicals

where children might get Intothem. Ingestion of this and

other PC board making chemi-cals can be very harmful andeven fatal, especially in small

children.

Fast removal of allmanner of etch resists canbe done with an acetonefree fingernail polish re-mover. It can be found nearthe fingernail polish in drugstores and discount storesetc.. It is a cheap and effec-tive way to go.

(Negative Photo Resist ..... continued from previous page.)

1.) Sunlight at about noon, for three minutes.2.) Datak no. ER-39 bulb, for 5-1/2 minutes ata

distance of 20".3.) Two F15T8BL bulbs 20 minutes at 15".

Step 5. Developing the PC Board...You need two metal or glass photo-

graphic trays for developing (never use plasticrtrays). If you work with small boards, find some

smaller trays which will save on developer.Use only Datak developer no. ER-8. Place enough developer in each trayso that the board is under the developer by about 1/16" when it is placedflat in the tray.Note: The resist pattern is transparent during developing and can-not be seen until it is completely dry.

Follow these developing steps:a.) Place exposed board in first tray for 30 to 45 seconds, gently

rocking the tray every five seconds. (Never touch the surface of theboard, the resist will scratch easily. Handle by the edges.)

b.) Remove board, holding by the edges. Allow it to drain for tenseconds and then place it face down on 2 or 3 layers of clean facial tissue(don't slide or rub!).

c.) Carefully remove tissue and immerse the board in second trayfor ten seconds. Remove, allow it to dry and inspect the pattern againstthe light (hold board flat and point it toward the light; sight along board).Good developing shows up the pattern clearly with no drain marks orstains in the areas to be etched. Old, used developer will leave globs atrandom.

Dry thoroughly before etching; at least ten minutes at room tem-perature. The resist must be hard before etching.

Step 6. Touch up. The board may now be handled in normal lighting.I nspect the board for breaks in traces or pads. If there are any, you cantouch them up with the etch resist pen. Repair any breaks before etching.I f the above steps were done well, touch up will probably not be needed.

Etch the PC board. (See section about etching.)00*

The Products...

(Continued on next page)

The no. ER-71 Photo Resist (left) is supplied in adark bottle which will prevent deterioration.Officially, the shelf life is about two years; but theactual life is probably much longer. It can bestored at room temperature; cooler temperatureswill add to the shelf life. Warm it up to at leastroom temperature to apply it. The Resist has aspray cap for application. Spin coating is alsogood if you are equipped to do it.

The no. ER-8 developer i s supplied in ametal can and will keep for a long time if kepttightly shut. If you plan to do quite a number or

boards, then you'll want to start with two cans. TheResist will cover about 1,700 square inches of copper but acan of developer won't develop nearly that much area. (Areawill vary with circuit density.)

10

THE WORK AREASHOULD BE WELL

VENTILATED; AVOIDBREATHING VAPORSand avoid skin contact.Do not use near open

flames or sparks.

Ferric Chloride etchantcan stain clothing (and justabout anything else) horri-

bly. Wear old cloths anddon't use this in an area

that can't take somestains. Work close to run-ning water; an immediatecold water flush can re-

duce staining, rinse out aneye etc..

Etching can be donei n an open, photo-graphic tray. If youkeep the tray coveredwith a piece of windowglass when not in use,i t will reduce thefumes and can bekept this way for manyhours.

NEVER add water to theEtch Powder Concentrate!Add the powder to water.

HEATING &Boiling !!

The mixing of water withFerric Chloride powder gen-erates considerable heat.You must add the powder tothe water; NEVER add wa-ter to the powder!

Used ferric chlorideetchant may bestored in plastic bot-tles for future use. Ifyou will be storing itfor quite awhile andthe bottle is not full,squeeze the bottle toeliminate most of the airspace. It should last manymonths.

ETCHING PC BOARDS

The ETCHING PROCESS.There are any number of chemicals that may be used as an

etchant. The only one that we recommend is Ferric Chloride. It is availablefrom some sources as a liquid and Datak supplies it in powder form to bemixed by the user with water. This is the most effective and economical ofthe etchants.

Factors that will accelerate the ferric chloride etching process areheat, oxygen and agitation. The etchant will work at room temperature butat higher temperatures (say, about 125 degrees F) it will work much fasterand cleaner. Agitation not only keeps moving fresh developer over thecopper, but introduces oxygen, which acts something like a catalyst.

Ferric Chloride is not an acid; the chemical process is one of dis-placement. We do not recommend acids for many reasons of safety andeffectiveness, disposal problems etc..

The etching container must be either glass or plastic. It can be assimple as a photographic tray (that you keep rocking gently) to the Dataketching tank, which bubbles air through the solution to provide both agitation and oxygen. A fish-tank type heater adds to the effectiveness of theetch tank. Agitation is very important and proper etching won't happenwithout fairly constant of the etchant during the entire process.

Using Datak Ferric Chloride ..... We always recommend that youWear eye protection and provide adequate ventilation. The fol-

l owing assumes that you will use an open, photographic tray. Mixing is thesame regardless of what devices you use during etching, i.e. the etchingtank, tray etc..

Step 1. Mix a package of Datak number ER-3 ferric chloride pow-der with 16 ounces of water. Add the powder slowly; expect heating of thewater as you go. Adding too fast can cause splattering due to the fastheating. An empty, plastic one gallon milk jug works fine for the process.Mix until all powder is dissolved. Then store the finished product in a plas-tic bottle. It will keep for a long time.

Step 2. Preheat the etchant. You could preheat the etchant by im-mersing its storage bottle in a bucket of hot water for twenty minutes be-fore pouring it into a tray. IT WILL EXPAND WHEN HEATED, LOOSENTHE BOTTLE CAP SO THE BOTTLE WON'T BURST. Or you could use aPyrex glass tray on a low-heat hot plate (etc.). A heat lamp could be usedon an open tray. Room temperature will work, but slowly.

Step 3. Etching can take from ten to twenty-five minutes. Immersethe PC board and continue agitation by rocking the tray gently, or liftingand immersing the board with a plastic tweezers etc..

Step 4. Inspect the board periodically and it will be obvious whenetching is complete. When finished, rinse the board with fresh water, wipeoff with paper towels. The process is completed and you are ready to drillthe board, remove the resist and load the parts.

You may pour used etchant back into the container to use it again.Replace the etchant when the process slows down considerably. Oldetchant may be flushed down the sink but be sure to follow-up with a vig-orous water chaser for two or three minutes. The etchant will dilute anddisperse quickly.

Users note: Ferric Chloride etchant is available from severalsources. Some is not of good quality and you will note that it isslow to act and etches only a very small volume of copper. Datakprovides a very high quality etchant and at a price that is betterthan some of the lower grade materials. We do strongly urge youto use the Datak product. Slow etching can cause undercutting,weakened resist and other problems.