Frequently Asked Questions
Q: What thermal conductivity test method was used to
achieve the values given on the data sheets?
A: The Anter Quickline 10 was used to run this test. Bergquist has
published an application note about the modifications to the
ASTM D5470 test method to appropriately test Gap Pad materials
at low 10 pressure (see Bergquist Application Note #112).
Q: Is Gap Pad offered with an adhesive?
A: Currently the standard Gap Pads, which include 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 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.
Q: What is meant by “naturally tacky”?
A: The characteristic of the rubber itself has a natural inherent tack,
without the addition of an adhesive. As with adhesive backed
products, the naturally tacky surfaces 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: Is the naturally tacky side of the Gap Pad reposition-
A: Again, depending on the material that the pad is applied to, in
most cases they are repositionable. Again, care should be taken
when removing the pad from aluminum or anodized surfaces as
to avoid tearing or delaminating the pad.The naturally tacky side
is always easier to reposition than an adhesive side.
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 liquid Gap Filler reworkable?
A: It is highly dependent on the strength of 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: In the temperature range of -60°C to 200°C, there is no
significant variance in hardness, for silicone Gap Pads and
Q: What is the life expectancy of Gap Pad?
A: The silicone rubber industry recognizes a 20-year life for
silicone rubber when used within specified operation parameters.
Bergquist has made pad material that has been in applications for
some 30 years without any known signs of deterioration.
Q: What is the shelf life of Gap Pad?
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: What are the upper processing temperature limits for
Gap Pad and for how long?
A: Gap Pads that are pink, mauve or gold in color 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 electrically isolating?
A: Yes, all Gap Pad materials are electrically isolating. However, keep
in mind that Gap Pad is designed to FILL gaps, not for
guaranteeing them in high stress applications.
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: Will Gap Pad and Gap Filler work in my application?
What size gaps will Gap Pad and Gap Filler
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
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 anything given off by the material (i.e. extractables,
A: 1) Gap Pad and Gap Filler, like all silicone pads, can extract silicone
fluid (refer to Bergquist Application Note #56). Also note that
Gap Pad and Gap Filler have the lowest extraction value for
silicone-based gap filling products on the market.
2) Primarily for aerospace applications, outgassing data is detailed
in Bergquist Application Note #117, tested per ASTM E595.
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.