Effective Masking Methods for Pcb Assemblies

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Ef fective Masking MethodsEf fective Masking Methods
for PCB Assembliesfor PCB Assemblies
Anda AutomationAnda Automation
Presented byPresented by

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Effective Masking for PCBEffective 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.

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

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

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

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

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

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

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

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

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Effective Masking MethodsEffective Masking Methods
There are some effectiveThere are some effective
methods that are used tomethods that are used to
mask difficult areas on thesemask difficult areas on these
types of difficult to coattypes of difficult to coat
assemblies.assemblies.

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

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

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

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Peelable Masking CompoundsPeelable Masking Compounds
One effective way to do thisOne effective way to do this
is through a peelable,is through a peelable,
masking compound usuallymasking compound usually
made out of latex.made out of latex.

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This compound is appliedThis compound is applied
and allowed to dry.and allowed to dry.
The method used for dryingThe method used for drying
can be either heat or aircan be either heat or air
dried or cured by UV.dried or cured by UV.

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Afterwards, the coating isAfterwards, the coating is
applied and allowed to dry,applied and allowed to dry,
as well.as well.
This peelable mask is thenThis peelable mask is then
peeled off, exposing thepeeled off, exposing the
clean contact pads.clean contact pads.

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

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Masking DotsMasking Dots
Another method that worksAnother method that works
involves using maskinginvolves using masking
dots.dots.
These are small stickers thatThese are small stickers that
usually come on a roll thatusually come on a roll that
you pull off and stick overyou pull off and stick over
the pad before coating.the pad before coating.

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Masking DotsMasking Dots
This method eliminates theThis method eliminates the
drying time that the peelabledrying time that the peelable
mask takes.mask takes.
The dots used need to beThe dots used need to be
silicone free or otherwise itsilicone free or otherwise it
can cause de-wetting of thecan cause de-wetting of the
coating.coating.

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Specialty TapeSpecialty Tape
The 3rd method is theThe 3rd method is the
application of special tape toapplication of special tape to
mask these sensitive areas.mask these sensitive areas.
The tape is usually made ofThe tape is usually made of
polyester.polyester.
Another tape called KaptonAnother tape called Kapton
tape is used, also.tape is used, also.

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The process is mainly theThe process is mainly the
same as mentioned in thesame as mentioned in the
previous applications.previous applications.
Like the masking dots, theLike the masking dots, the
tape adhesive has to be non-tape adhesive has to be non-
silicone based, or there willsilicone based, or there will
be a lack of adhesion by thebe a lack of adhesion by the
coating or some de-wetting.coating or some de-wetting.

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

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Best Practice for De-maskingBest Practice for De-masking
The PCBs should have theThe PCBs should have the
masking removed as soonmasking removed as soon
as the coating feels dryas 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 bethe masking material may be
more difficult to removemore difficult to remove
from the coating.from the coating.

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When this happens, theWhen this happens, the
coating can be damaged orcoating can be damaged or
can peel off during de-can peel off during de-
masking.masking.
This will cause unnecessaryThis will cause unnecessary
touch up of the coatingtouch up of the coating
when conformal coating forwhen conformal coating for
pcb assemblies to give it thepcb assemblies to give it the
required cosmeticrequired cosmetic
appearance it needs.appearance it needs.

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

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

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

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

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

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Any conformal coatingAny conformal coating
machines or othermachines or other
equipment that applyequipment that apply
coating to masked areas willcoating to masked areas will
have difficulty providing ahave difficulty providing a
good finished product if thegood finished product if the
masking material ismasking material is
composed of siliconecomposed of silicone
polymers.polymers.

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

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Effective Masking Methods for Pcb Assemblies

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Effective Masking Methods for Pcb Assemblies