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Gap Pad   >> Frequently Asked Questions
  Q: What thermal conductivity test method was used to achieve the values given
     on the data sheet?

A: A test fixture is utilised that meets the specifications outlined in ASTM D5470.

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 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 anodised surfaces to avoid tearing or delamination.

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 rubber itself has the tack. Tack strength varies from one Gap Pad product to the next.

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 anodised surfaces as to avoid tearing or delaminating the pad. The side with natural tack 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 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: 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 live is (6) six months after the date of manufacture. After these dates, inherent tack and adhesive properties should be recharacterised.

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.

Q: What are the upper processing temperature limits for Gap Pad and for how long can Gap Pad be exposed to them?
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 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: How much force will the pad place on my device?
A: Refer to the Pressure vs. Deflection chart 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 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: 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 be the material (e.g. extractables, outgassing)?
A: 1) Silicon Gap pad and Gap Fillers, like all soft silicone materials, can extract silicone fluid (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 detailed in Bergquist Application Note #117, tested per ASTM E595.

Q: Why does the data sheet describe the hardness rating as a bulk rubber hardness?
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 250mil 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.

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