In high-performance electronics, thermal interface materials (TIMs) are the unsung heroes that allow heat to flow from hot components into heat spreaders, chassis, or heat sinks. Among these, gap pads have become essential for bridging uneven surfaces and filling air gaps with a thermally conductive medium. But beyond thermal conductivity, and compliance, one attribute is gaining new importance: the ability to reposition, or reuse a gap pad without compromising assembly integrity.
Repositionable vs. Reusable: Two Different Attributes
These two terms often get blurred, but they are not the same:
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Repositionable: The pad can be shifted during the original installation to achieve correct placement before final compression. This helps avoid scrapping a pad, or PCB assembly if alignment is slightly off.
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Reusable: The pad can be removed after full installation and compression, then redeployed again—whether in rework, field service, or iterative prototyping. This requires the pad to maintain mechanical integrity and surface compliance even after multiple uses.
Understanding this distinction is critical for engineers designing assemblies with tight tolerances, iterative service requirements, or expensive components that cannot risk adhesive misalignment.
Compression Set: The Silent Determinant of Reusability
One of the most overlooked properties of gap pads is compression set — the material’s tendency to retain deformation after being compressed.
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Low compression set means the pad rebounds when pressure is released, maintaining thickness and surface conformity over multiple assembly cycles. This is ideal for reusability.
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High compression set means the pad stays “crushed” after one use, reducing its ability to fill gaps on subsequent installs. These pads may be repositionable during the first install but rarely reusable afterward.
For example:
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Tflex™ HR600, HR400, HR6.5, HR7.5 — engineered silicone gap fillers with relatively low compression set, making them good candidates for both repositionability, and limited reusability.
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Gap Pad® 1000HD — while mechanically robust (92 Shore 00 hardness), its higher density can lead to more compression set under high clamping force, which favors repositionability but limits long-term reuse.
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Gap Pad® 1450 — with a balance of 1.4 W/m·K conductivity and 80 Shore 00 hardness, this pad resists tearing and has moderate compression set, giving it better repeat performance in rework scenarios.
Compression set becomes critical when assemblies go through thermal cycling. A pad with poor rebound may start to lose surface contact, degrading thermal performance over time.
Material Examples: Conductivity, Hardness, and Rework Potential
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Tflex™ HR600 – 3.0 W/m·K, 25 Shore 00, low compression set; remains compliant for multiple reuses.
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Tflex™ HR400 – 2.0 W/m·K, 40 Shore 00, moderate compression set; strong balance of compliance and toughness.
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Tflex™ HR6.5 – 6.5 W/m·K, 60 Shore 00, higher firmness, but maintains structure under repeated compressions. Tflex™ HR6.5 is a common thermal pad NEDC die-cuts.
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Tflex™ HR7.5 – 7.5 W/m·K, 70 Shore 00, excellent heat transfer, slightly higher compression set but still repositionable during install.
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Gap Pad® 1000HD – 1.0 W/m·K, 92 Shore 00, very firm; highly repositionable but typically single-use due to compression set.
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Gap Pad® 1450 – 1.4 W/m·K, 80 Shore 00, robust with moderate compression set; capable of limited reuse.
How No-Tack Surfaces Enable Repositionability
Some manufacturers offer gap pad variants with “no tack on one side”, such as Laird’s –DC1 suffix. This configuration has adhesive or tack on one face for stability, but leaves the opposite surface free for:
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Easier initial placement: The non-tacky side slides into position before compression, critical when aligning pads with fine features or cutouts.
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Reduced scrap rate: If the pad lands slightly off, it can be lifted, realigned, and placed again without damaging the pad or leaving adhesive residue.
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Cleaner rework: Assemblies can be disassembled without fighting adhesive pull-off forces on both sides.
This makes the –DC1 style a powerful tool for both repositionable installs and partial reusability in development cycles. Keep in mind less tack on one side, is significantly less thermal performance than tacky both sides.
Why It Matters for Engineers
In many thermal applications, the pad itself is only a small fraction of the overall assembly cost—but improper installation, rework delays, or thermal degradation from compression set can drive costs exponentially higher.
Repositionable and reusable gap pads help mitigate this risk:
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Reduced Assembly Scrap – Pads can be shifted into place instead of discarded for minor misalignment.
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Faster Prototyping – Reusable pads support iterative design without wasting consumables.
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Serviceability – Field technicians can replace boards or modules without needing a full replacement pad stock.
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Long-Term Reliability – Pads with low compression set maintain consistent thermal performance after thermal cycling.
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Lower Total Cost of Ownership – Even higher-priced materials like Tflex HR7.5, or Gap Pad 1450 may save money over time by reducing rework hours and consumable waste.
Final Thoughts
As thermal demands climb with next-generation GPUs, ASICs, and power devices, engineers need more than just high W/m·K performance—they need materials that work with their assembly processes. Repositionable and reusable gap pads, when paired with low compression set, not only conduct heat effectively but also protect production yields and reduce lifecycle costs.
And when precision matters most, selecting a no-tack surface option like Laird’s –DC1 suffix can make the difference between fighting alignment errors and achieving flawless thermal performance.