Quality Assurance Requirements for Coating No Clean Solder PCBs

ANDA AUTOMATION
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Quality Assurance:Quality Assurance:
Requirements for CoatingRequirements for Coating
No Clean Solder PCBsNo Clean Solder PCBs
Anda AutomationAnda Automation
Presented byPresented by

ANDA AUTOMATION
Requirements for Coating NoRequirements for Coating No
Clean Solder PCBsClean Solder PCBs
It is important for conformal coating to fulfill a
function of protecting the substrate on a
printed circuit board (PCB).
To be effective the coating has to adhere to it
for its expected service life.

ANDA AUTOMATION
Requirements for Coating NoRequirements for Coating No
Clean Solder PCBsClean Solder PCBs
Because the substrate and lack of surface
preparation have an effect on the adhesion of
the conformal coatings, a method to measure
the adhesion of a coating to different surface
treatments, or of different coatings to the
same substrate and treatment, is vital in many
industries.

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Coating on No Clean Solder isCoating on No Clean Solder is
AllowedAllowed
No-clean soldering materialsNo-clean soldering materials
come in pastes, cored wirescome in pastes, cored wires
with liquid fluxes that arewith liquid fluxes that are
used for assembly.used for assembly.

ANDA AUTOMATION
AllowedAllowed
Many of today’s solderMany of today’s solder
pastes are designed to havepastes are designed to have
a softer residue to enhancea softer residue to enhance
in-circuit properties ofin-circuit properties of
testing.testing.

ANDA AUTOMATION
AllowedAllowed
It is perfectly acceptable toIt is perfectly acceptable to
apply the designatedapply the designated
conformal coating on top ofconformal coating on top of
no-clean solder and fluxno-clean solder and flux
residue.residue.

ANDA AUTOMATION
AllowedAllowed
The PCB cured by theThe PCB cured by the
manufacturer’smanufacturer’s
recommendation shouldrecommendation should
cure without incident.cure without incident.

ANDA AUTOMATION
AllowedAllowed
In order to follow all qualityIn order to follow all quality
procedures and haveprocedures and have
documentation to presentdocumentation to present
internally to qualityinternally to quality
assurance, it is importantassurance, it is important
that there are nothat there are no
compatibility issues in yourcompatibility issues in your
coating process orcoating process or
conformal coatingconformal coating
equipment.equipment.

ANDA AUTOMATION
AllowedAllowed
It also helps to document itIt also helps to document it
for later discussions withfor later discussions with
the stakeholders as to thethe stakeholders as to the
feasibility of the newfeasibility of the new
method.method.

ANDA AUTOMATION
Determine Adhesion PropertiesDetermine Adhesion Properties
It is recommended that youIt is recommended that you
determine that the fluxdetermine that the flux
materials used in the nomaterials used in the no
clean process won’t causeclean process won’t cause
any adhesion problems withany adhesion problems with
the conformal coating usedthe conformal coating used
on the PCB.on the PCB.

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Document it thoroughlyDocument it thoroughly
before proceeding inbefore proceeding in
accepting this procedure asaccepting this procedure as
a standard process.a standard process.

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Material suppliers thatMaterial suppliers that
solder products or apply thesolder products or apply the
coating to them can oftencoating to them can often
perform a laboratory test toperform a laboratory test to
determine compatibility of adetermine compatibility of a
no clean flux residue withno clean flux residue with
the coating material that youthe coating material that you
will be using.will be using.

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You can also perform thisYou can also perform this
test on your own bytest on your own by
purchasing the rightpurchasing the right
supplies and using thesupplies and using the
appropriate tests.appropriate tests.

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Coating adhesion isCoating adhesion is
measured with a peel testmeasured with a peel test
that can be applied to thethat can be applied to the
PCB.PCB.

ANDA AUTOMATION
The choice of tape in a peelThe choice of tape in a peel
test is critical in achievingtest is critical in achieving
complete wetting of thecomplete wetting of the
fabric, and good adhesion tofabric, and good adhesion to
the coating.the coating.

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The tape is applied withThe tape is applied with
liquid coating to theliquid coating to the
substrate, and then cured,substrate, and then cured,
leaving a flapping and un-leaving a flapping and un-
bonded section for clampingbonded section for clamping
on during the pull test.on during the pull test.

ANDA AUTOMATION
ASTM Method 3359-92a canASTM Method 3359-92a can
be used as the appropriatebe used as the appropriate
test method for testingtest method for testing
coating in the no cleancoating in the no clean
procedure--the process isprocedure--the process is
described below.described below.

ANDA AUTOMATION
Method 3359-92aMethod 3359-92a
The tape test method isThe tape test method is
suggested as a quicksuggested as a quick
identifier as to determineidentifier as to determine
whether the coating iswhether the coating is
adequately adhering to theadequately adhering to the
substrate of the PCB:substrate of the PCB:

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Make an X-cut throughMake an X-cut through
the film with athe film with a
carbide tip tool to thecarbide tip tool to the
substrate.substrate.
Apply pressure-Apply pressure-
sensitive tape is oversensitive tape is over
the cut.the cut.

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Smooth the tape isSmooth the tape is
smoothed into placesmoothed into place
over the incision areaover the incision area
with a pencil eraser.with a pencil eraser.
Pull the tape quicklyPull the tape quickly
back over itself withback over itself with
as close to 180º angleas close to 180º angle
as possible.as possible.

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Assess the adhesionAssess the adhesion
on a 0 to 5 scale.on a 0 to 5 scale.
Document the findingsDocument the findings
in a standardizedin a standardized
quality procedure.quality procedure.

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It is strongly suggested toIt is strongly suggested to
allow the boards toallow the boards to
completely cool off beforecompletely cool off before
applying any conformalapplying any conformal
coating pcb assemblies; thiscoating pcb assemblies; this
allows the flux residues toallows the flux residues to
properly solidify and dry allproperly solidify and dry all
the way.the way.

ANDA AUTOMATION
It also aids the adhesionIt also aids the adhesion
properties because theproperties because the
liquid coating will be appliedliquid coating will be applied
to the solidified residues ofto the solidified residues of
the flux instead of one thatthe flux instead of one that
would be softer or more likewould be softer or more like
a fluid.a fluid.

ANDA AUTOMATION
In many examples, no-cleanIn many examples, no-clean
flux residues are veryflux residues are very
compatible with urethanecompatible with urethane
and acrylic conformaland acrylic conformal
coating for pcb assemblies.coating for pcb assemblies.

ANDA AUTOMATION
Usually incompatibilityUsually incompatibility
problems arise with silicone-problems arise with silicone-
based coatings becausebased coatings because
there are some ingredientsthere are some ingredients
in those some fluxes thatin those some fluxes that
can inhibit the curing.can inhibit the curing.

ANDA AUTOMATION
In all cases it is better toIn all cases it is better to
perform appropriate testingperform appropriate testing
to validate the compatibilityto validate the compatibility
between the conformalbetween the conformal
coating and the flux.coating and the flux.

ANDA AUTOMATION
It is also a good idea to alsoIt is also a good idea to also
have this discussionhave this discussion
beforehand with thebeforehand with the
customer to explain thecustomer to explain the
difference in the no cleandifference in the no clean
process if they are notprocess if they are not
familiar with all aspects of it.familiar with all aspects of it.

ANDA AUTOMATION
The results coming fromThe results coming from
using testing Method 3359-using testing Method 3359-
92 should be used as proof92 should be used as proof
positive that good adhesionpositive that good adhesion
properties are staying inproperties are staying in
place during all manual-place during all manual-
coating processes and alsocoating processes and also
with the use of conformalwith the use of conformal
coating machines.coating machines.

ANDA AUTOMATION
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Quality Assurance Requirements for Coating No Clean Solder PCBs

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