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PCViper UltraKit - Heatsink Lapping kit

Heatsink Lapping Kit
13th September 2004
Manufacured By
Supplied By



Plenty of people have discussed the merits (or lack of) of lapping your heatsink. Some swear by it claiming it can gain the 5 or more degrees Celsius extra cooling while others see it as a labour-intensive way to get almost no benefit.

I think the truth is that lapping will help increases heat transfer from your CPU to your heat sink base, but by how much depends on the condition of both to begin with. I have no doubt that truly attrocious base finish can benefit to the tune 5 or even more degrees of cooling, but a base that's fairly true to start with isn't going to deliver you so much.

I'm sure you've all seen the diagrams but for the few of you who haven't, here goes:

Because neither surface is perfectly flat there are a few contact areas but there are also a lot of places where neither of the surfaces actually meet. As I'm sure you can imagine, heat from the core travels easily across the contact areas but, due to the relatively low thermal conductivity of air, it has a much tougher job bridging the areas where there is no contact.

Unlapped ~ No Thermal Grease


This is the reason why thermal compounds are so important when fitting a heat sink. The thermal compound has a much higher thermal conductivity than air and so helps heat to bridge the gaps where air would normally reside. The thermal compound filled areas still aren't as efficient at shipping heat as those in physical contact but the solution is still vastly preferable to dry mating of the surfaces.

Unlapped ~ With Thermal Grease


There is however a further step that can be taken to improve thermal transmission and that is to abrade away (or lap) the imperfections in one or, ideally, both mating surfaces.

As you can see, with just the heat sink base lapped, there is an increased amount of contact and a reduced volume of thermal compound. If you ever wondered why it'd important not to use too thick a layer of thermal grease, this is why. You want just enough to fill the surface pits and not so much that it forms a cushioning layer that keeps the two surfaces apart.

HSF Lapped ~ With Thermal Grease


Naturally, the progression to this is to lap both mating surfaces which, if done properly, would virtually eliminate the need for any kind of thermal interface between the two. That said I think I'd still use a thin smear of a very fine silver or ceramic based compound which may well still do some good on a microscopic level.

HSF and Core Lapped


The last heatsink lapping I reviews was a paper only kit. While you can get some extremely fine grit papers, they don't come close to the level of finish you can get from a quality lapping compound.

The kit I want to test today comes from PCViper, a small company but one that clearly believes tin the personal approach to customer service. The website, the instructions and the whole transaction smacks of that rarest of commodities, a freindly service from folk who obviously care about what they sell. The downside to being a small company is that at present, they only accept payment by PayPal Cashiers Checks and Money Orders but most of us have access to at least one of these so no biggie.

Although PCViper sell this as a kit suitable for pretty poor quality sinks, I personally think it needs an additional sheet of 320 grit paper to cope with some of the worst sinks. Not necessarily that you won't get deep scratches out with the supplied three papers, but if the base has a high spot, or worse still a low spot, there may not be enough abrasive power to cut back that much material.

Here's what your money buys you.

The kit contains:

  • 400, 600 and 800 grit sandpaper.
  • A single use syringe of our level 1 lapping compound.
  • A single use syringe of our level 2 lapping compound.
  • A single use syringe of our level 3 lapping compound.
  • Three alcohol soaked cotton pads.

Let's give it a whirl!

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