Frequently Asked Questions
Q:
What thermal conductivity test method was used toachieve the values given on the data sheets?
Q:
What are the upper processing temperature limits
for Gap Pad and for how long can Gap Pad be exposed
to them?
A:
A test fixture is utilized that meets the specifications outlined in
ASTMD5470.
A:
Gap Pad VO materials and Gap Pad A3000 are more stable at
elevated temperatures.Gap Pad in general can be exposed to
temporary processing temperatures of 250°C for five minutes
and 300°C for one minute.
Q:
Is Gap Pad offered with an
adhesive?
A:
Currently,Gap Pad VO,Gap Pad VO Soft,and Gap Pad VO Ultra
Soft are offered with or without an
adhesive on the Sil-Pad
800/900 carrier-side of the material.The remaining surface has
natural inherent tack.All other Gap Pads have inherent tack.
Q:
Is Gap Pad electrically isolating?
A:
Yes,all Gap Pad materials are electrically isolating.However,
keep in mind that Gap Pad is designed to FILL gaps and is not
recommended for applications where high mounting pressure is
exerted on the Gap Pad.
Q:
Is the
adhesive repositionable?
A:
Depending on the surface being applied to,if care is taken,the
pad may be repositioned.Special care should be taken when
removing the pad from aluminum or anodized surfaces to avoid
tearing or delamination.
GAP PAD
Q:
How much force will the pad place on my device?
A:
Refer to the Pressure vs.Deflection charts in Bergquist
Application Note #116.
Q:
What is meant by “natural tack”?
A:
The characteristic of the rubber itself has a natural inherent tack,
without the addition of an
adhesive.As with
adhesive-backed
products,the surfaces with natural tack may help in the assembly
process to temporarily hold the pad in place while the application
is being assembled.Unlike
adhesive-backed products,inherent tack
does not have a thermal penalty since the rubber itself has the
tack.Tack strength varies from one Gap Pad product to the next.
Q:
Will Gap Pad and Gap Filler work in my application?
What size gaps will Gap Pad and Gap Filler
accommodate?
A:
Gap Pad and Gap Filler can be used wherever air can be
replaced,such as between a heat-generating device and a heat
sink,heat spreader or housing.This can be done using one sheet
of Gap Pad or individual pieces of appropriate thicknesses,or by
using Gap Filler if stack-up tolerances and height variations
are significant.
Q:
Can Gap Pad with natural tack be repositioned?
A:
Again,depending on the material that the pad is applied to,in
most cases they are repositionable.Care should be taken when
removing the pad from aluminum or anodized surfaces as to
avoid tearing or delaminating the pad.The side with natural tack
is always easier to reposition than an
adhesive side.
Q:
What is meant by “compliance” and “conformability,”
and why is this important?
A:
The better a Gap Pad complies and conforms to a rough or
stepped surface,the less interfacial resistance will be present due
to air voids and air gaps.This leads to a lower overall thermal
resistance of the pad between the two interfaces.
Q:
Is Gap Pad reworkable?
A:
Depending on the application and the pad being used,Gap Pad
has been reworked in the past.Bergquist has customers that are
currently using the same pad for reassembling their applications
after burn-in processes and after fieldwork repairs.However,this
is left up to the design engineer’s judgment as to whether or not
the Gap Pad will withstand reuse.
Q:
Is anything given off by the material
(e.g. extractables, outgassing)?
A:
1) Silicone Gap Pad and Gap Fillers,like all soft silicone materials,
can extract siliconefluid (refer to Bergquist Application Note#56).Also note that Gap Pad and Gap Filler have some of the
lowest extraction values for silicone-based gap filling products on
the market and if your application requires no silicone,see our
line of Sil-Free material.2) Primarily for aerospace applications,outgassing data is detailedin Bergquist Application Note #117,tested per ASTM E595.
Q:
Is liquid Gap Filler reworkable?
A:
It is highly dependent on the application and its surface topography.
Liquid Gap Filler will cure with low
adhesive strength to the
application surfaces.
Q:
Will heat make the material softer?
A:
From -60°C to 200°C,there is no significant variance in hardness
for silicone Gap Pads and Gap Fillers.
Q:
Why does the data sheet describe the hardness rating
as a bulk rubber hardness?
Q:
What is the shelf life of Gap Pad?
A:
A reinforcement carrier is generally utilized in Bergquist Gap Pads
for ease of handling.When testing hardness,the reinforcement
carrier can alter the test results and incorrectly depict thinner
materials as being harder.To eliminate this error,a 250 mil rubber
puck is molded with no reinforcement carrier.The puck is then
tested for hardness.The Shore hardness is recorded after a 30
second delay.
A:
Shelf life for Gap Pad is one (1) year after date of manufacture.
For Gap Pad with
adhesive,the shelf life is six (6) months after
the date of manufacture.After these dates,inherent tack and
adhesive properties should be recharacterized.
Q:
How is extraction testing performed?
A:
The test method used is the Bellcore Extraction method
#TR-NWT-000930;refer to Bergquist Application Note #56. 8
