CPU shim
A spacer that stabilizes heatsinks and protects CPU packaging.
A CPU shim, sometimes called a CPU spacer, sits between the processor and its heatsink. It stabilizes the heatsink during installation, reducing the risk of damaging the CPU’s delicate packaging, and helps spread the heatsink’s weight evenly across the surface. These shims are typically made from thin, very flat aluminum or copper. Copper dissipates heat well but conducts electricity, so a non-conductive shim is important to avoid accidental short circuits. Aluminum shims are often anodized, which makes them non-conductive and can improve their look for case modding. Correct thickness is critical: if the shim is too thick, the heatsink won’t contact the CPU, leading to poor cooling and possible overheating. Most shims are CNC-machined, often with laser cutting; cheaper stamped or pressed versions may be less accurate.
CPU shims are rare in OEM computers. They are used by some hardware enthusiasts who install heavier heatsinks for quieter, cooler, or overclocked systems. A heavy heatsink puts extra pressure on the CPU and motherboard, so shims help those who frequently swap CPUs, heatsinks, or cooling setups, or who use a heatsink heavier than the manufacturer’s recommended weight. These shims are now largely obsolete because most modern home-user processors—since the Athlon 64 and Pentium 4—include an integrated heat spreader (IHS) that protects the CPU core from accidental breakage.
- Material
- Thin, very flat aluminium or copper
- Manufacturing
- Most are CNC manufactured, often using laser cutting; cheaper ones may be pressed or stamped
- Usage context
- Used by some computer hardware enthusiasts, not common in OEM computers
- Obsoleteness
- Largely obsolete since the introduction of the Athlon 64 and Pentium 4 with Integrated Heat Spreaders (IHS)
Lore & Background
CPU shims are usually made of thin and very flat aluminium or copper. Copper has good heat dissipation capacity but is electrically conductive, so CPU shims should be non-conductive to prevent accidental short circuiting. Aluminium shims are often anodized, which makes them non-conductive and improves their appearance, a practice seen in case modding. Proper thickness is critical: if the shim is too thick, the heatsink will not make contact with the CPU, resulting in poor cooling and possible overheating.
Most shims are CNC manufactured, often using laser cutting. Cheaper ones may be pressed or stamped, which could make them less accurate. CPU shims are not common at all in OEM computers, but are used by some computer hardware enthusiasts who may use heavier heatsinks because they wish to have a cooler or less noisy system or perhaps to overclock the CPU for better performance. A heavy heatsink puts more pressure on the CPU and motherboard, and shims are very useful for people who often change CPU, heatsink or cooling solutions, or use a heatsink heavier than the CPU manufacturer's recommended weight.
CPU shims are nowadays largely obsolete because most modern processors designed for home users since the introduction of the Athlon 64 and Pentium 4 have an Integrated Heat Spreader (IHS), which prevents the CPU core from being accidentally broken.
Reader's Guide
The significance of the CPU shim lies in its role as a protective and stabilizing component for CPU cooling, particularly before the widespread adoption of integrated heat spreaders. By providing a flat, even surface between the CPU and heatsink, it reduced the risk of cracking the fragile CPU die during installation, especially when using heavy aftermarket heatsinks for overclocking or silent operation. Its use was largely confined to enthusiast builders who frequently swapped components or sought better thermal performance, as OEM computers rarely included them.
However, the introduction of the Integrated Heat Spreader (IHS) on processors like the Athlon 64 and Pentium 4 made the CPU shim largely obsolete for home users. The IHS itself protects the CPU core, eliminating the primary need for a separate shim. Despite this, the shim remains a historical footnote in computer cooling, illustrating the transition from bare-die processors to more robust packaging. Its legacy is also seen in the continued use of thermal interface materials and careful heatsink mounting practices, though the shim itself is no longer a common accessory.
Did You Know?
- CPU shims are also called CPU spacers.
- Copper shims are electrically conductive, while anodized aluminium shims are non-conductive.
- A shim that is too thick can prevent the heatsink from contacting the CPU, causing overheating.
- CPU shims are largely obsolete due to the Integrated Heat Spreader (IHS) on modern processors.
Frequently Asked Questions
What is a CPU shim and what does it actually do?
A CPU shim, sometimes called a CPU spacer, is a thin metal plate placed between the processor and its heatsink. It stabilizes the heatsink during installation and spreads its weight evenly so the fragile CPU packaging underneath isn't stressed or cracked.
What material is a CPU shim made from?
Most shims are CNC-machined or laser-cut from very thin sheets of aluminum or copper, though cheaper ones may simply be stamped or pressed. Aluminum versions are frequently anodized, which renders them non-conductive and gives them a polished look popular in case modding.
Why did CPU shims become largely obsolete?
The shift to Integrated Heat Spreader (IHS) designs on chips like the Athlon 64 and Pentium 4 replaced the fragile exposed die with a sturdy metal lid. Once that protective cap became standard, the spacer's original purpose of shielding delicate packaging was no longer needed.
What's the practical difference between an aluminum and a copper CPU shim?
Copper is an excellent heat conductor but also conducts electricity, which introduces a real risk of accidental short circuits. Aluminum shims, particularly when anodized, are non-conductive and are generally the safer and more visually appealing choice for enthusiasts.
Do I still need a CPU shim in a modern PC build?
For virtually every current processor with an integrated heat spreader, a shim is unnecessary and adds no meaningful benefit. They remain a niche item of interest mainly to hardware enthusiasts who build with older exposed-die CPUs or who collect parts for aesthetic modding.
More in Computer Cooling and Sound Cards 1-24
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced