effective masking methods for pcb assemblies

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E f fe c t i ve M a s ki n g M e t h o d sE f fe c t i ve M a s ki n g M e t h o d sfo r P C B A s s e m bl i e sfo r P C B A s s e m bl i e s

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Effective Masking for PCB Effective Masking for PCB AssembliesAssemblies

Many businesses often encounter issues with getting conformal coating in sensitive keep out areas.

The main part of this problem goes back to how connectors and terminals are manufactured.



They are typically manufactured by inserting them (terminals and contacts) from the bottom of the insulator housing.



By doing this, many By doing this, many connectors are susceptible connectors are susceptible and open to contamination and open to contamination from the conformal coating from the conformal coating that can wick in unwanted that can wick in unwanted areasareas



In most situations, the In most situations, the housing of the insulator sits housing of the insulator sits right above the solder leads right above the solder leads to aid in conventional to aid in conventional electronic manufacturing electronic manufacturing processes and will act to processes and will act to improve the efficiency of the improve the efficiency of the cleaning process. cleaning process.



The low viscosity of many The low viscosity of many conformal coatings make it conformal coatings make it challenging to keep the challenging to keep the conformal coating away conformal coating away from these critical contact from these critical contact areas when using conformal areas when using conformal coating equipment.coating equipment.



There are a wide variety of There are a wide variety of application methods and application methods and materials available, but materials available, but viscosity is still difficult for viscosity is still difficult for manufacturers to control.manufacturers to control.



Applying masking to these Applying masking to these challenging areas is a challenging areas is a common practice to protect common practice to protect the contact pads. the contact pads.



If you have a large volume of If you have a large volume of boards you have to coat, a boards you have to coat, a selective coating robot may selective coating robot may be a better long-term choice be a better long-term choice for conformal coating pcb for conformal coating pcb assemblies, largely assemblies, largely eliminating or cutting down eliminating or cutting down the need to mask.the need to mask.



Automated coating cuts Automated coating cuts down on the areas that need down on the areas that need to be masked on a PCB to to be masked on a PCB to almost nothing, but there almost nothing, but there are still areas that need are still areas that need masking. masking.


Effective Masking MethodsEffective Masking Methods

There are some effective There are some effective methods that are used to methods that are used to mask difficult areas on these mask difficult areas on these types of difficult to coat types of difficult to coat assemblies. assemblies.



They work well, even for the They work well, even for the most stubborn area that is most stubborn area that is often difficult to cover up, often difficult to cover up, the contact pads for the contact pads for switches. switches.



It is difficult to efficiently It is difficult to efficiently mask these contact pads, mask these contact pads, but luckily there are some but luckily there are some ways that make this easier ways that make this easier to accomplish. to accomplish.



There are a few suggested There are a few suggested options available to do this, options available to do this, and these materials are and these materials are designed to peel easily away designed to peel easily away from the contacts after from the contacts after coating, allowing you to coating, allowing you to remove the coating from the remove the coating from the keep-out area.keep-out area.


Peelable Masking CompoundsPeelable Masking Compounds

One effective way to do this One effective way to do this is through a peelable, is through a peelable, masking compound usually masking compound usually made out of latex. made out of latex.



This compound is applied This compound is applied and allowed to dry. and allowed to dry.

The method used for drying The method used for drying can be either heat or air can be either heat or air dried or cured by UV.dried or cured by UV.



Afterwards, the coating is Afterwards, the coating is applied and allowed to dry, applied and allowed to dry, as well. as well.

This peelable mask is then This peelable mask is then peeled off, exposing the peeled off, exposing the clean contact pads. clean contact pads.



This liquid mask is excellent This liquid mask is excellent for masking contacts, card for masking contacts, card edges, gold fingers, and edges, gold fingers, and other keep out areas during other keep out areas during conformal coating conformal coating applications.applications.


Masking DotsMasking Dots

Another method that works Another method that works involves using masking involves using masking dots. dots.

These are small stickers that These are small stickers that usually come on a roll that usually come on a roll that you pull off and stick over you pull off and stick over the pad before coating.the pad before coating.


Masking DotsMasking Dots

This method eliminates the This method eliminates the drying time that the peelable drying time that the peelable mask takes. mask takes.

The dots used need to be The dots used need to be silicone free or otherwise it silicone free or otherwise it can cause de-wetting of the can cause de-wetting of the coating. coating.


Specialty TapeSpecialty Tape

The 3rd method is the The 3rd method is the application of special tape to application of special tape to mask these sensitive areas. mask these sensitive areas.

The tape is usually made of The tape is usually made of polyester. polyester.

Another tape called Kapton Another tape called Kapton tape is used, also. tape is used, also.



The process is mainly the The process is mainly the same as mentioned in the same as mentioned in the previous applications. previous applications.

Like the masking dots, the Like the masking dots, the tape adhesive has to be non-tape adhesive has to be non-silicone based, or there will silicone based, or there will be a lack of adhesion by the be a lack of adhesion by the coating or some de-wetting. coating or some de-wetting.



This method is more labor-This method is more labor-intensive than the previous intensive than the previous method, but the tape can be method, but the tape can be ordered pre-cut for high ordered pre-cut for high volume coating needs. volume coating needs.


Best Practice for De-maskingBest Practice for De-masking

The PCBs should have the The PCBs should have the masking removed as soon masking removed as soon as the coating feels dry as the coating feels dry when you touch it. when you touch it.

If you wait longer than that, If you wait longer than that, the masking material may be the masking material may be more difficult to remove more difficult to remove from the coating.from the coating.



When this happens, the When this happens, the coating can be damaged or coating can be damaged or can peel off during de-can peel off during de-masking. masking.

This will cause unnecessary This will cause unnecessary touch up of the coating touch up of the coating when conformal coating for when conformal coating for pcb assemblies to give it the pcb assemblies to give it the required cosmetic required cosmetic appearance it needs. appearance it needs.



Other suggestions for a Other suggestions for a clean mask removal include clean mask removal include applying a little thinner to a applying a little thinner to a cotton bud and dampening cotton bud and dampening the area prior to de-masking the area prior to de-masking with a curved pair of smooth with a curved pair of smooth tweezers. tweezers.



The thinner will soften the The thinner will soften the coating to eliminate tears coating to eliminate tears and the tweezers are a good and the tweezers are a good aid for quick removal of aid for quick removal of kapton tape and masking kapton tape and masking dots.dots.



Conformal coating printed Conformal coating printed circuit boards require a circuit boards require a great deal of finesse and great deal of finesse and accuracy in the process to accuracy in the process to yield a high quality finished yield a high quality finished product, especially in the product, especially in the highly sensitive keep out highly sensitive keep out areas.areas.



When conformal coating pcb When conformal coating pcb assemblies, the main thing assemblies, the main thing to note is that there are now to note is that there are now several types of masking several types of masking available from different available from different vendors that will cover up vendors that will cover up sensitive areas, such as sensitive areas, such as connector pads. connector pads.



If you have a large volume If you have a large volume shop, then a selective shop, then a selective conformal coating machine conformal coating machine may be a better choice in the may be a better choice in the long term because it cuts long term because it cuts down the need to mask down the need to mask areas on the PCB. areas on the PCB.



Any conformal coating Any conformal coating machines or other machines or other equipment that apply equipment that apply coating to masked areas will coating to masked areas will have difficulty providing a have difficulty providing a good finished product if the good finished product if the masking material is masking material is composed of silicone composed of silicone polymers. polymers.



The coating will not adhere The coating will not adhere in this case, so exercise in this case, so exercise caution when procuring caution when procuring your masking material.your masking material.


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effective masking methods for pcb assemblies

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