Conformal Coating Over

Existing Process Residues

Barry Ritchie

Loctite Corporation

www.Loctite.com

ABSTRACT

Faster - smaller - cheaper are the key buzzwords that drive today's electronicmanufacturing processes from concept to reality. If you're building PWB's, SMT's,MCM's, COB's or maybe CSP's, the need to improve existing technologies with better,safer and more reliable materials and processes has given rise to a wide variety of newchemistries and process options.

This large, rather confusing array of material choices and processing options, has givenbirth to a new manufacturing need:

A better understanding of "what effects what”, on the surface of the printed wiring boardor substrate.

Speaking from a conformal coating standpoint, which is usually the final step in mostelectronic manufacturing processes, "even a minor change in the cure of a solder maskcan have a serious impact on the success of other processes". Un-volitized flux specieson the surface, for example, can also be a difficult problem to track down if one is notwell versed in the complete manufacturing processes and all the various materials thatcan be encountered in an electronics assembly line.

Because the coating is usually the last material applied to the circuit assembly, it cansometimes get blamed for other types of problems. In most cases, it is not the coating, butsomething under the coating that can attribute to a failure mechanism. The point being"who better to ask than a coatings engineer, as to what is on the board and what problemsit may cause? " Because coatings are applied last and are all transparent films, theproblems and indications seen here can be signs of big trouble on the board if ignored ornot fully understood.

This technical paper will help identify compatibility issues and proactive procedures thatwill help the engineer understand exactly what to look out for when using, considering orcontracting out product for conformal coating operations.

Conformal coatings are polymeric materials, which are used to protect metallic junctionson electronic assemblies from a wide variety of life cycle contaminants. Conformalcoatings provide a high degree of insulative protection and are usually resistant to manytypes of solvents and harsh environments encountered in the product life cycle. Thecoating materials also act to immobilize various types of particulate on the surface of thePCB and function as protective barriers to the various devices on the board.

They are extremely resistant to moisture and humidity and are often applied as an afterthought (not originally part of the initial design), to quiet down electrical bias andpotential arcing during high humidity operating conditions, especially on fine pitchassemblies. They can also remedy other electrical problems on the board that can occuras a result of the environment the electronic device must perform in.

The primary chemistries are:

• AR = Acrylic Resin• ER = Epoxy Resin• UR = Urethane Resin• SR = Silicon Resin• XY = Parylene

These resin systems are primarily made up of monomers, oligomers, de-foaming agents,fillers, and wetting agents. Various combinations of each are added to the formulationsto adjust the particular cured and uncured properties. Solvents were, and still are,typically added to adjust application viscosity. They "flash off" by solvent evaporation,leaving the resin matrix and this initiates the cure. High VOC emissions associated withthis type of cure created a need for more environmentally acceptable productionchemistries and cure mechanisms.

All, except the parylenes, have traditionally been solvent based until a decade ago whenenvironmental issues dictated a need to change. Now, many materials are solvent-freechemistries (100% solids). The ability to ultra violet (UV), cure is commonplace. Thisnew generation of conformal coating materials has also given birth to HYBRID coatingswhich contain two or more resin systems to achieve superior properties, i.e.: ARUR.

Even though there are several chemical categories there are really only two liquidfamilies. These can be broken down to Organic and Silicone.

Organic coatings encompass AR, ER, and UR materials. They typically have bettermoisture and chemical resistance. They are tough abrasion resistant materials with usefuloperating ranges from – 400 C to +1250 C. These resins can be used alone orcombined to adjust properties and rheology of the uncured and cured material. Manyhave been formulated to be UV curable to increase in line cure speeds.

One major problem encountered with the UV hybrid materials was an inability to cure thematerial under components not irradiated by UV energy. Introducing a secondary heatstep basically defeated the purpose of a high speed UV curing option and at the sametime placed a great deal of stress onto the solder joints of the components in which thematerial was being cured. The hydraulic force and expansion of the wet uncured coatingunder components would cause solder joint fatigue, component body cracking orpopcorning (see figure 1), of the previously UV cured coating fillet surrounding the part.This was soon corrected with secondary cure mechanisms that would react to ambientmoisture and/or a catalyst.

FIGURE 1POPCORNING OF SINGLE COMPONENT UV COATING

Silicone coatings are extremely useful materials when components see extremetemperature cycling environments such as automotive applications. The useful operatingrange of these materials is – 550 C to + 2040 C. They are very forgiving materialsin production because they coat over and stick to just about any surface found on a circuitboard and offer good resistance to polar solvents. Cross contamination factors stemmingfrom the use of silicones and the effects on other production processes is no longer amajor concern with the solvent-free non-volatile chemistries that can be easily handledwith proper housekeeping practices. Secondary cure for the UV curable versions isaccomplished with a very effective ambient moisture mechanism.

Under certain types of operating conditions such as high heat and low air flow, siliconescan evolve "cyclics", which can interfere with mechanical relays and playback heads byforming a thin layer of silica on the contact surfaces. This causes an increase in theelectrical resistance, and should be used with caution in areas where mechanical contactsand tape decks reside directly over the coating in these types of operating environments.

Most environmentally acceptable coating chemistries combine multiple resins to improvenot only the properties, but improve the wetting characteristics and adhesion to the widevariety of commonly used substrates and solder masks. Solvents are no longer requiredto cure the resins by "solvent evaporation" or to adjust application viscosity.

Along with the advent of new conformal coatings, solder mask manufacturers came upwith a new line of solder masks designed to perform better with smaller pitch linespacing. To enhance solderability, the flux manufacturers invented multiple varieties oflow residue (formerly known as no clean fluxes), and water soluble fluxes. Thosemanufacturers who decided to continue to clean electronic assemblies were overwhelmedwith new replacement cleaning chemistries that swarmed the market.

All of these new materials hit the market at approximately the same time as (1) a directresult of the environmental issues associated with the manufacture of printed wiringboards, and (2) the need for faster speed, smaller size and higher I/O count ofcomponents.

Isaac Newton proved that…

"For every action there is an equal and opposite reaction"

… and this law certainly holds true when such a wide variety of new materials hitthe production lines at the same time.

Many materials have worked fine in coexistence with each other through the multipleoperations in PWB manufacture but if anything should change, identifying the culprit andthe effect, can be a difficult and time consuming task. Production usually comes to anabrupt halt. An accurate process history is definitely the key to successful diagnosis here.

Diagnosing Problems

The First Step:

Before one can diagnose and treat and understand potential in-line manufacturing relatedsurface problems, there are a few "knowns" that must first be identified. Withoutknowing what the base line is, it is impossible to know exactly where you are in yourprocess. A baseline is knowing where all the parameters need to be to produce a goodfunctional board which is also free from harmful residues when it arrives in the coatingarea.

A thorough understanding of the complete process line from start to finish as well as thechemical materials used is the most important. A few simple things that the engineer caneasily check without performing extensive and costly testing such as SIR in-line testing,FT-IR (Fourier transform- infrared spectroscopy), and Ion Chromatography to mention afew, are as follows:

SOLDER MASKS

The first item is the application of solder mask. This is often out of the direct control ofthe board assembler and the responsibility here usually lies with the bare board fabricator.The solder mask process is rather elaborate and includes etching, plating, fusing andcleaning materials. If the polymer mask materials are not applied to clean,uncontaminated substrates, a multitude of problems can impact several assemblyprocesses down stream.

Elemental compositions of fillers typically found in solder mask technologies includesilicon, which is most likely from glass and fiber fillers. Other elements which can bedetected via (Energy Dispersive X-ray Spectrometry (EDS), and FT-IR spectral analysis

are aluminum, magnesium, calcium and titanium. There are varied levels of eachcomposition for each type of solder mask. To confirm that the variation was not due todifferent analysis locations, spectrums were acquired from several locations on thespecimens. [1]

Surface topography also varies between the many types of gloss, semi-gloss and mattefinishes. This will have an impact on both wetting characteristics and the adhesion of theconformal coating. (See figure 2)

FIGURE 2SOLDER MASK SURFACE TOPOGRAPHY

(Olympus BH-2 Microscope in Reflectance Mode at 50X Magnification)

Enthone DSR 3241 MD

Ciba Giegy Probimer 52

Ciba Giegy Probimer 65M

One common problem that occurs frequently is improperly cured solder mask. Manytypes are now photoimagable, which means that the artwork is imaged via aphotolithography step. This artwork may be aligned and imaged accurately, but if thefinal thermal bake out is not performed for the exact recommended time and temperaturedictated by the solder mask supplier, many process substances can leach out to thesurface usually during a heat excursion phase such as soldering. This effects the surfaceenergy on the board and can cause surface tension wetting and adhesion problems for theconformal coating. It can also contribute to electro chemical migration under the coating.High ionics is another factor to consider if the solder mask has not been applied correctly.

If the base substrate is contaminated, adhesion of the solder mask will be jeopardized.Many different types of fusing fluids can also be detected via FT-IR analysis. Someindicators of this scenario include high ionics and poor solder mask adhesion onincoming inspection [2]. (Some FT-IR spectra are included in Table 4).

The recommendation for these situations is to know what the baseline is for a particularsolder mask. [3] This means performing cleanliness and adhesion testing on a samplebatch of boards provided by the board fabricator. By using a cross hatch / tape pull testsuch as the method in IPC-SM840B, (IPC-TM-650 2.4.28), results of adhesion of thesolder mask before and after soldering excursion(s) can be screened prior to building abatch of boards. The bare sample test board should be subjected to all solderingexcursions, checking adhesion before and after via the cross-hatch method. [2] This is adestructive test but is well worth the cost of an unassembled bare board. If the squaresare falling off after this test, the likelihood of a contaminated substrate under the soldermask is very high. Continuing to proceed with manufacture of the affected batch ofboards should be in question at this point. (See figure 3)

FIGURE 3SOLDER MASK CROSS HATCH

Solvent extraction methods found in most production environments are not incrediblyaccurate but are good production monitoring checks. Examples of typical systemsinclude the Omega Meter™, Ionograph™ and Zero Ion™ systems. Any dramaticincrease in the level of chlorides, (micrograms per square inch), from the pre-establishedbaseline should be a flag that ionic species from the solder mask process have not beenproperly driven off in the cleaning and/or bake cycles [4]. Once a board fabricatorrealizes that you are performing these two simple incoming inspection tests, they will beunlikely to send you any panels that may have been "short cycled" or improperlyprocessed. This approach works very well providing that the manufacturing engineeringteam has 1) an incoming screening method, and 2) the baseline information on knowngood lots of a particular types of solder masked boards. Obviously, not all solder masksare the same, but if not correctly applied and cured, can exhibit similar indications.

The adhesion of the conformal coating to the solder mask substrate utilizes this samerecommended test method. The only other method currently used is visual inspectionafter thermal and humidity cycling. The industry is diligently working to evolve neweradhesion testing methods for conformal coatings but progress is slow going. Sheartesting using bare FR4 to solder mask lap shears will determine overall strength of theadhesive bond but isn't reliable for all curing chemistries.

Peel testing of fiberglass woven cloth saturated in the coating material [5], isn't realisticas the thickness is generally over 8 mils due to capillary action. Some adhesion testingresults of various conformal coatings over various solder masks can be found in Tables 1- 3. It is important to note that all candidate solder masks tested were applied and curedby the solder mask suppliers. All conformal coatings were applied, cured and tested inthe Electronics Application Laboratories of the Loctite North American EngineeringCenter.

Table 1

Shear / Pull Strength Adhesion Testing Measured in Peak Load Pounds:

Method for Table 1 Testing:

1. One 1.0" x 2.0" FR4 lap shear and one solder mask lap shear overlapped 1.0" with aninduced (shim), .005" gap All specimens were manually spray coated while wettingcharacteristic were monitored. The wet coating specimens were clamped and curedper the manufactures recommended primary and secondary cure profile.

2. Pull testing was performed after 14 days at ambient to allow for UV and solventsecondary cures to complete on those specific material chemistries.

3. An Instron 4204 MTS with Sintech ReNew Software Upgrade Package was used tomeasure break of the specimens. A 50 kn load cell was used with a 0.05"/min. tensilehead rate. (See figures 4 and 5)

SolderMask

3241MD

3241 G 3241GCR

3241GI

3241PGHC

3300G

Prob.52

Prob.65

Prob.77

BareFR4

Solvent

Coating Type Y/N

394 UV ARUR N 362.1 344.5 406.2 350.1 327.1 348.5 422.0 401.5 412.9 290.1

FailureMode

Coating Coating Coating 2% sm 70% sm Coating Coating Coating Coating Coating

397 ARUR N 674.0 1235.1 829.3 984.6 1043.8 1033.6 1423.9 697.7 376.1 1417.6

FailureMode

25% sm 75% sm 25% sm 60% sm 90% sm 25% sm 20% sm Coating Coating Coating

5290 UVSR

N 18.2 <15.0 <15.0 <15.0 19.0 <15.0 17.4 19.0 <15.0 23.7

FailureMode

Coating Coating Coating Coating Coating Coating Coating Coating Coating Coating

5293 UVSR

N <15.0 56.1 20.5 26.9 30.8 37.9 34.0 22.1 37.5 39.5

FailureMode

Coating Coating Coating Coating Coating Coating Coating Coating Coating Coating

1B31L AR Y 83.0 56.9 54.5 37.1 68.7 36.3 109.0 58.5 37.1 109.0

FailureMode

Coating Coating Coating Coating Coating Coating Coating Coating Coating Coating

1A33 UR Y 340.6 230.7 261.7 312.1 270.2 83.0 361.0 360.3 381.3 361.0

FailureMode

Coating Coating Coating Coating Coating Coating Coating Coating Coating Coating

UV 79 AR N 500.2 612.4 474.1 369.8 591.1 434.6 695.4 690.6 501.0 346.9

FailureMode

30% sm 30% sm 25% sm 5% sm 25% sm 2% sm Coating 2% sm 5% sm Coating

Failure Mechanisms:

Coating = Coating to substrate failure without removal of solder mask.

(There were no failures to the FR4 lap shear sides)

sm = Percent of solder mask removed during shear testing.

FIGURE 4FIXTURED TEST SPECIMEN

FIGURE 5COATING LAPS AFTER SHEAR

Table 2

Conformal Coating Cross Hatch / Tape Pull Adhesion Results Plotted After Full Cure:

Method for Table 2 and Table 3 testing:

1. All specimens were manually sprayed with the selected coatings. Wettingcharacteristics on the various solder masks were monitored and the specimens werethen cured per the supplier recommend cure profiles.

2. A series of 11 parallel cuts were made through the coating (min. 1" length), and thesubstrate was rotated 90 degrees. An additional 11 parallel cuts were made within the1.0" surface area of the test specimens.

3. This cross hatch method resulted in 100 cut blocks within a 1" x 1" area on the testspecimens.

4. Tape (1" width, 5 lb./in.), was placed and pressed over the cross hatch site. It wasthen pulled sharply off at a 450 degree angle, revealing the number of coating blocksremoved from the solder mask. This was verified in a fluorescent inspection box.(See figure 6)

Mask3241MD 3241 G

3241GCR

3241PGI

3241PGHC 3300 G

Prob.52

Prob.65

Prob.77

BareFR4

Coating %Failure

%Failure

%Failure

%Failure

%Failure

%Failure

%Failure

%Failure

%Failure

%Failure

394 0% 0% 0% 0% 0% 1% 12% 92% 100% 0%

397 0% 0% 0% 0% 0% 0% 0% 28% 97% 0%

5290 0% 0% 0% 0% 0% 0% 0% 0% 24% 0%

5293 0% 0% 0% 0% 0% 0% 0% 0% 8% 0%

1B31L 27% 40% 74% 42% 54% 100% 0% 2% 100% 4%

1A33 0% 0% 0% 0% 0% 0% 0% 0% 0% 0%

UV79 0% 0% 0% 0% 0% 0% 0% 2% 4% 0%

Table 3

Conformal Coating Cross Hatch / Tape Pull Results Plotted After Thermal / HumidityAging @ 85C/85% x 120 Hours:

Mask 3241MD

3241 G 3241GCR

3241PGI

3241PGHC

3300 G Prob. 52 Prob. 65 Prob. 77 BareFR4

Coating%

Failure%

Failure%

Failure%

Failure%

Failure%

Failure%

Failure%

Failure%

Failure%

Failure

394 0% 0% 0% 0% 0% 12% 18% 82% 22% 0%

397 0% 0% 0% 0% 0% 0% 0% 12% 8% 0%

5290 0% 0% 0% 0% 0% 0% 0% 0% 24% 0%

5293 0% 0% 0% 0% 0% 0% 0% 0% 8% 0%

1B31L 88% 92% 100% 100% 100% 100% 0% 0% 100% 6%

1A33 0% 0% 0% 0% 0% 0% 0% 0% 0% 0%

UV79 0% 0% 0% 0% 0% 8% 0% 22% 6% 0%

FIGURE 6CROSS HATCH / TAPE PULL AFTER COATING

WATER SOLUBLE FLUX CHEMISTRY (WSF)Typically, these materials are highly aggressive (organic acid), OA fluxes. The goodnews is that "if" adequately cleaned, neutralized and dried immediately after the solderingprocess, the result yields a clean assembly, which is usually an ideal candidate forconformal coating. Inadequately cleaned assemblies usually exhibit high ionic levels.Another important step here is insuring that the assembly is completely dry prior toconformal coating. In most cases the WSF candidates are excellent choices simplybecause they are cleaned off after the solder processes.

LOW SOLIDS FLUX CHEMISTRY (LSF, formerly known as No Clean Flux)

These materials can also be ideal candidates providing that they are applied andprocessed correctly [4]. The solder excursion profile is extremely important to thesuccessful volatilization and/or evaporation of the ionic and corrosive species in the flux.The solder profile should be adjusted to the type, size and topography of the assemblyand its components. Tall and high mass components can rob heat from the solder sitesleaving higher levels of unvolitized flux species in these areas. Monitoring thetemperatures of the solder pad areas while setting the profile will provide accuratetemperature readings in these sites as opposed to unpopulated planar sites which areusually chosen for attachment of the thermocouples. Remarkable differences intemperatures on different sites of the board will most likely be revealed.

Ionic cleanliness testing performed on these types of fluxes can be frustrating. After thealcohol used in the test solution evaporates from the board, there can be a whitediscoloration of the solder joints. (See figure 7)

FIGURE 7LSF RESIDUE AFTER IONIC TESTING

This is a cosmetic issue but nonetheless has caused a massive reduction in the amount ofroutine first piece ionic cleanliness testing performed on low reside fluxes, simplybecause of the aesthetics. Some manufactures have decided not to use this test at all onLSF chemistries.

The problem with not performing ionic cleanliness testing is the fact that unvolitizedionic and corrosive species will give birth to a variety of corrosive and electricalproblems on the board under humidity and electrical bias. The conformal coating willretard these corrosion cells but will not completely prevent them from forming.Indicators here are dendrite growth, premature corrosion, high ionics and visible residueson and around the solder joints. A properly volatized low residue flux should becompletely free of visible soldering residues or stains into the surrounding solder mask.Wave solder applications usually do a good job of completely volatizing the harmfulspecies but solder reflow of stenciled solder pastes require a higher degree of control ofthe solder reflow profile to properly volatize the corrosive species. SIR testing shouldmonitor this type of process.

SOLDER TOUCH UP

Very often after inspection and / or test, the need arises to perform a solder touch upoperation on a rejected solder joint or a faulty component which needs to be replaced.The same scenarios can occur as mentioned above if these flux residues are not removedor neutralized prior to the conformal coating application.

COMPONENT CLEANLINESS

De-wetting of conformal coating materials on certain types of components is a commonproblem, (figure 8). It can effect the solvent-based materials as well as the solvent freeformulations. It can sometimes be remedied with the right type of application method.

There are many types of proprietary mold release agents such as wax and polysiloxanes(silicones), that are used by the packaging industry. Most are added to the plasticpackage mixture prior to injection molding to facilitate removal. In some cases themarking inks used to mark the nomenclature can also contain species that effect surfacetension.

FIGURE 8COMPONENT DEWETTING

Although some may argue that this is not a functional problem as long as the conductorleads have conformal coating coverage, others may look at it differently as an aestheticsissue to the end user. The bottom line is that this condition exists and can be a majorproblem in the conformal coating operation.

Component cleanliness should be monitored on incoming inspection. The problemsassociated with de-wetting of the conformal coating are difficult to fix. Multiple cleaningsteps can be required to remove these films and in some cases the temperatures associatedwith the soldering excursion are enough to cause these contaminants to continuouslyleach to the surface and migrate to other areas of the assembly.

This can also effect other adhesive applications such as attaching heat sinks to ASICdevices with thermally conductive adhesives. It can be evident on discrete and passivedevices as well as some types of connector bodies.

The only solution here is to specify a conformal coating chemistry, which has beenformulated with the correct rheology to wet these types of surfaces and correct surfacetension problems. Discussing this phenomenon with the package suppliers is also a goodidea. They can usually recommend cleaning or priming agents to improve this situation.Most are reluctant to reveal their release agent formulations.

ALTERNATE CLEANING AGENTS

Cleaning a soldered electronic assembly is a wise step prior to the application of anyconformal coating or adhesive, but cannot always be done in production for a multitudeof reasons. With the multiple cleaning chemistries designed to be drop in replacementsfor Freon™® TMS™ and 1,1,1, trichloroethane, one needs to consider evaporationtimes, flash points and understand the types of residues that can become resident to theassembly depending on the type of cleaner employed.Many of the alternate cleaning chemistries can leave oily residues behind and have verylong evaporation times. Any of these residues can contribute to poor wetting andadhesion of the conformal coating if not properly processed. Some materials have verylittle cleaning action and can actually cause more harm to a PWB assembly than notcleaning it at all. The following is a list of some of the replacement cleaning chemistriesand the pros and cons of each one:

ALIPHATIC HYDROCARBONS:

Petroleum Distillates have mild odors and long evaporation times.

Naptha Blends have low odor and fast evaporation times.

Isoparaffins have a mild odor and fast evaporation times.

AROMATIC HYDROCARBONS:

Have strong odors, good cleaning capabilities, higher toxicity, long evaporation times andleave a slight residue.

ESTERS:

Lactate Blends have long evaporation times, have a strong odor and leave residues.

N-Butyl Butyrate has long evaporation times and an offensive odor.

TERPENES (d-limonene):

Have an oily reside, a strong citrus odor and good cleaning capabilities.

ALIPHATIC / AROMATIC HYDROCARBONS:

Have a mild to medium odor, long evaporation times and are excellent degreasers,(mineral spirits).

CONCLUSIONS:

The data collected during these screening tests indicated the following:

The wetting characteristics of the wet coating materials varied on the solder maskspecimens until the coating thickness approached approximately .0035" (3.5 mils). Atthis thickness the surface tension problems appeared to subside in most cases, primarilydue to the bulk of coating material applied.

Table 1 indicates the various adhesive strengths of the coating materials tested overspecific solder masks and bare FR4 substrate.As indicated by Table 2, adhesion of the conformal coatings varied greatly on differentsolder mask technologies. It was also noted that various heat excursions on the soldermask chemistries yielded different surface energy characteristics.

Conformal coating "wetting" characteristics varied on different solder mask technologiesat varying thickness'.

As indicated in Table 3, adhesion of the conformal coatings to some solder masksactually improved in some cases after thermal and humidity cycling.

SUMMARY:

Understanding "what effects what" on the surface of the printed wiring board, isimperative to a successful conformal coating operation. [6]. The lessons learned here canprevent potential production disasters not only in the conformal coating operation, but inother areas of production and will insure a reliable electronic assembly process.

The dominating Conformal Coating Specifications MIL-I-46058C and IPC-CC830, areslated to soon be replaced by IPC-CC-830A [7], as the Industry Standard. Many of therequirements have been modified, removed or incorporate updated realisticrecommendations. Users should familiarize themselves with this document.

"The amount of adhesion between conformal coatings and substrates varies greatly.Among the factors which influence the adhesion is the conformal coating type, thecoating and curing process, the soldering process used, flux type, flux cleaning (if any),solder mask type and manufacturer. The key to the adhesion requirement is agreementbetween the applicator and the end user as to what level of adhesion produces afunctional assembly and what test (if any) shall be used to insure that sufficient adhesionhas been achieved and maintained through any tests or environmental conditioning,(IPC-CC830A, Paragraph 6.7, October 1998).

Table 4SOLDER MASK SPECTRA

(UMA-500 &ndash;FT-IR Microscope equipped with a SpectraTech ATR Adapter with apenetration depth of approx. 1 um, and allowed for the spectra to be acquired directly

from the solder mask)

Enthone DSR 3241MD

Ciba Giegy Probimer 52

Ciba Giegy Probimer 65M

Acknowledgment:

Information, comments and data provided by my colleagues Les Bennington, Phill Kroppand Jamie Serenson is gratefully acknowledged.

The author would like to thank Roger Landolt, Durand Cercone of Enthone&ndash;OMI,and Les Moreland of Ciba Specialty Chemicals Corporation, for their guidance andcooperation.

References:

[1] Serenson, J., Loctite Corporation, Marongelli, S., Universal Instruments, "The Effectof Solder Mask and Surface Mount Adhesive Types on a PCB Manufacturing Process",Presented at Nepcon West '99 TS-16

[2] DeBiase, J, LaCroce, S., Landolt, R., Enthone-OMI Inc., "Compatibility of PWBCoatings with Assembly Processes", Electronic Packaging and Production, February1996.

[3] Ritchie, B., , Loctite Corporation, "Conformal Coating Over Solder Mask, No CleanSoldering and Alternate Cleaning Technologies", Presented at NEPCON West '94 TS-25.

[4] Sandia National Laboratories, "A Report from the Low Residue Soldering TaskForce", Low Residue Soldering for Military and Commercial Applications, June1995

[5] Vazirane,G., Kaiser Electronics, "Conformal Coats and Their Compatibility withSolder Masks", IPC-TP-1059, Presented at IPC 1992 Fall Meeting.

[6] Ritchie, B., Loctite Corporation, "Process Requirements for Solvent-Free UVConformal Coatings", Adhesives in Electronics '96, Second International Conference onAdhesive Joining and Coating Technology in Electronics Manufacturing, Stockholm,Sweden, June 1996

[7] IPC-CC-830A, was completed by the Conformal Coating Task Group in October1998 and is currently available through the IPC.