Our Lapped CPU Heatsink Test Platform

Lapping the CPU in a heatsink test platform is probably a controversial move that’s bound to provoke reactions. Funny thing is, it was done a year ago, and photos of the CPU showing the copper top exposed by the lapping have been featured in many of our reviews. Yet, not a single comment. This article goes through the problems, investigations and explorations that led us to lap our Core i7-965 Extreme test CPU, and analyzes the results and implications.

Anyone who’s been reading SPCR for even a short portion of our 10+ year history
knows that we take consistency and repeatability seriously. Our vision for SPCR
is a database library for computer gear acoustics and thermal behaviour consistent
enough so that you can compare something reviewed today with one in the same
class of gear reviewed years ago. This usually means using the exact same base
components in a test platform, using the same high precision measurement tools
(whether it be for degrees, decibels, watts, grams, millimeters or millivolts).
We’ve worked hard to stay true to this vision.

For testing CPU heatsinks, we’ve maintained from the start that a real CPU
and a real motherboard are are necessary, they cannot be replaced with any simulations,
no matter how much more convenient they may be. Not only does a CPU covered
with an Integrated Heatspreader (IHS) simply not behave the same way thermally
as a CPU-shaped copper plate heated by an electric coil beneath it, the heatsink
mounting hardware can rarely be attached the same way as on a motherboard. The
mounting system and its ease of use, its ability to apply high, even pressure
to the CPU/heatsink interface are critical. This aspect of heatsink testing
usually gets shortchanged when a non-CPU/motherboard test platform is used.

THE MOVE TO A 130W TDP i7-965 EXTREME TEST PLATFORM

But as CPUs, sockets and motherboards came and went through their increasingly
shorter life cycles, we’ve had to upgrade our test platform periodically. This
means there are a few unavoidable discontinuities in our database. Besides,
there’s little point comparing, for example, a heatsink for a 65W P4 on a 775
socket against a heatsink for a 130W i7 on a LGA2011 socket: They are completely
incompatible.

The last big change in our CPU heatsink test platform was a switch in January
2010 from the previous 95W TDP Intel Pentium D950 on anAsus P5Q-EM board
to a 130W TDP 3.2
GHz Core i7-965 Extreme with an Asus P6T SE motherboard. There were
two main reasons for the change:

The D950 was not challenging enough any more: The D950 CPU simply
didn’t run as hot as the latest socket 1366 i7 processors that had become
the new performance kings at the time. The old platform could not differentiate
enough between the high performance heatsink models designed to take on processors
that run 35W hotter. A hotter 130W 1366-socket processor would help differentiate
the A+ rank from the A and A- performers.

No more replacement parts, mainly, the motherboard of the old platform:
A motherboard used as a CPU heatsink testing platform takes a huge amount
of abuse. Intel informed me years ago that CPU sockets are designed for maybe
20 reliable uses. Oh, it will generally survive beyond that number of CPU
insertions and removals, but the point is that it’s reasonable for motherboard
and motherboard component makers to build them for a moderate amount of handling.
CPUs, motherboards and heatsinks are components that usually get seriously
handled only a few times in their lifespan, during installation, a CPU upgrade,
or maybe a heatsink upgrade. But our CPU heatsink test platforms get handled
— and manhandled — every time we test a heatsink. The CPU gets pulled
off and put back on at least a couple times, and the heatsink is often installed
and removed as many as half a dozen times in our examination of the installation
process. In fact, the Asus P5Q-EM that was our test platform in 2010 was actually
the second sample of that model used with the D950 CPU for heatsink testing;
we’d already broken the first one. We would not be able to get a third sample;
more unused samples of that model simply could not be found any more. This
was another good reason for a change.

The LGA1366 i7-965E Cooler Test Platform

TROUBLE IN PARADISE?

Since the 3.2 GHz Core i7-965 Extreme CPU and Asus P6T SE motherboard
came into service (nearly four years ago now), we’ve tested over 40 heatsinks
on this platform. This is not all of the heatsinks we’ve reviewed, only the
larger coolers designed for top performance. Some 20 or so less ambitious models
were tested on a cooler-running AMD test platform, then later, on a 95W TDP
Intel socket 1155 platform that replaced it.

We — and presumably most of our audience — have been reasonably pleased
with the performance of our 1366 test platform. The newer LGA2011 socket has
not seen a further increase in CPU heat; the TDP of all LGA2011 CPUs remains
at 130W, which keeps the thermal core of our test platform perfectly relevant.
Admittedly, one socket 2011 model, the i7-3970X, is rated for 150W, but this
$1000 item is an outlier; CPU TDP continues trending downwards. Even the heatsink
mounting mechanism for the LGA2011 hasn’t really changed much from LGA1366.
Fundamentally, no one had any quibbles with our testing methodology or the accuracy
and relevance of our results. Of course, no one tests CPU coolers at the extremely
low noise levels that we do routinely.

Still, a few heatsink sample suppliers have been less satisfied, and they’ve
implied once or twice that SPCR could be biased for some brands. One of the
more public of these incidents of supplier dissatisfaction occured a year ago
with the Dark Rock 2 Tower
Heatsink, three samples of which were submitted by be quiet! All
three samples exhibited mediocre performance, especially given the large size
and surface area of the fins. All three had poor contact footprints between
their bases and the CPU, which seemed largely responsible for the poor performance.

The bequiet! representative questioned whether our testing method could be
flawed, because, apparently, other reviewers had achieved good results. He even
asked whether our use of voltage control instead of PWM control for the cooling
fan could have played a part in the poor results. In an effort to dispel any
hint of foul play or error on our part, I took extra steps to examine and re-test
the three samples in great detail, adding an
extensive postscript that conclusively showed the poor contact between
the Dark Rock 2 Tower bases and the top of our test LGA1366 CPU.

That postscript contains two key photos and captions which I reproduce here:

Imprint of Thermal Interface Material on CPU and base of Dark Rock 2. A line on the top and bottom edges of the heatsink, matched on the CPU, shows where the TIM has been pressed away. Yet, the TIM in the center still has those fractal-like striations. This is conclusive evidence that the base of the bequiet! Dark Pro 2 sample here is concave.

Desired TIM imprint with the same CPU/motherboard, and a Prolimatech Megahalems heatsink. The heatsink was turned 90 degrees for the above photo, and the TIM was smudged a bit during removal, but you can clearly see the matching imprints of the TIM on the base and on the CPU. Both have a central area where there is very little TIM; it’s been pushed from the center due to very tight contact. Only around the periphery are there any striations of the TIM. This cooler performed a whopping 12°C better than the Dark Rock 2.

These images are reproduced because they show how and why the profile of the
heatsink base can have a dramatic effect on CPU cooling performance. The left
photo shows that the contact between the DP2 base and the CPU surface was actually
tightest along the perimeter of the CPU rather than at the center,
where there was an obvious gap and no metal-to-metal contact. Since the center
is where the CPU die resides, this is where it is hottest, and where the bond
between heatsink and IHS is critical.

IHS/CPU FLATNESS

After this issue with the Dark Pro 2 was put to rest, some questions about
our testing platform began nagging me:

1. Is the degree of concavity in our i7-965E normal?
2. Was it there before we started using it as a heatsink test plaform? Did
   it become more concave as a result of the pressure it was subject to with
   umpteen heatsinks that have slightly convex bases and high pressure mounting
   hardware?
3. Do other CPUs exhibit a similar degree of concavity?

Checking the flatness of the test CPU was relatively easy. We lined up its
surface with several aluminum or steel straight edges in turn, and compared
visually. As suspected, the i7-965 Extreme exhibited a small degree of concavity.
We have no instruments capable of measuring such minute gaps, but suffice it
to say there was a visible gap. Without a straight edge to compare closely,
however, this concavity is hard to see with the naked eye. It’s also difficult
to get a photo of this gap or concavity without a really good macro lens, although
we did managed to get photos
of various heatsink base flatness in a review of a couple of Scythe heatsinks
back in August 2010. Our point with those photos was that the best performing
heatsinks have bases that are flat or slightly convex, never concave.

Now, we’ve known that most CPUs equipped with an IHS — all desktop models
for a decade — are either flat or have slight concavity. We’ve discussed
this in the forums and in many of our heatsink reviews (like the one mentioned
above).

Question #1 isn’t easy to answer; we’d need a dozen or so unused and
used 1366 processors to compare. This is out of the question, as we have just
two 1366 models in total, and it is impossible for us to accumulate the large
number of new samples needed. Question #2 is also impossible to answer, as we
did not record the degree of concavity (or flatness) on our CPU before it was
put into service. Question #3 we could tackle somewhat, at least with the stable
of CPUs on hand in the SPCR lab. So… after examining some 30 CPUs, most of
them used with a heatsink for at least a few hours and a few that have never
been used, we can say that a small degree of concavity seems fairly normal in
most CPUs, but then again, a few of the never used CPUs seem to be just about
perfectly flat.

CONVEX BASES & DEFORMING PRESSURE

I mentioned these issues to a contact for another heatsink brand. His response
electrified us:

“Thermalright’s use of convex bases is well documented. Our
product managers have seen coolers tested following a Thermalright
that lost up to 2~3 degrees Celsius of performance. [sic] Buying a
brand new CPU to redo the test will reveal the same pattern: A flat base CPU
cooler tested before and after a Thermalright cooler will show slight loss
of performance. As a result of this, we always make sure to test Thermalright
coolers and others that are also convex last.

“However, there are exceptions such as CPUs with smaller die/heat spreader,
which aren’t as easily deformed due to smaller surface area. If you look
around the web, reviewers with older platforms that have bigger CPUs such
as the LGA1366 you guys used that have gone through a lot of tests would likely
all have concave CPUs. Consequently Thermalright coolers (and those that are
convex) tend to dominate in these roundups.”

Thermalright is named explicitly by this contact, but many other heatsinks
have slightly convex bases as well. They include models from Prolimatech, Phanteks,
Scythe and a few from Noctua. Some of these heatsinks feature mounting mechanisms
capable of very high pressure. All, not surprisingly, have had models that performed
very well on our 1366 test platform. Our LGA1366 CPU has taken them all on;
the implication is that it must be more concave than it was when new.

I decided to query a few reviewers and heatsink manufacturers about this issue.
My email to the select few:

“A sample supplier recently claimed that heatsinks that have a convex
base will reshape the CPU surface slightly after mounting them. The implication
is that it makes the IHS concave (or more concave) & makes cooling worse
with flat base heatsinks. Have you ever experienced or heard of this? Have
you considered it? What are your thoughts? I trust you use a stock non-lapped
CPU for testing? If the claim is true, then it could be argued that all HS
tested after tight mounting of a convex base heatsink must be biased from
that point onward for convex bases… and HS with non-convex bases will perform
worse than they would with a non-reshaped IHS CPU. It gives me a headache
to think about how to resolve this if the claim is true.”

Some failed to reply, and not all the answers were useful. Matt, a fellow hardware
reviewer who’s been at it for a long time, replied generously:

“Interesting topic. I’ve always enjoyed SPCR cooling articles,
by the way.

“My first impression is that it seems like a pedestrian claim. Like
someone just heard they are convex, and is making a derogatory claim off the
cuff without any quantitative measurement or further supporting information.
I’ve heard the convex claims before in the forum, though.

“So yes, some heatsinks have a slightly convex base but I haven’t
seen it actually measured, likely because it would be a hard thing to accurately
quantify – we’re talking millimeters and less here, and who knows what
their manufacturing tolerances are. It wasn’t that long ago when we were
looking at heatsink bases to feel how bad ridges were with our thumbnail,
but at least smoothness seems to have improved over the years. I’m not
sure I’d have much confidence in how convex the bases are from one sample
to the next – I’m sure there would be some kind of range. Again
though, I’ve never seen a reliable measurement on how convex a base is
though. JoeC did some pressure testing, but not specifically looking at what
we’re talking about here, and not in a controlled environment to really
analyze this: http://www.overclockers.com/heatsink-mounting-pressure-vs-performance/

“Taking this one step further, does a convex HS possess the ability to
warp the IHS? Maybe. Doubtful. And if we’re honest, I’d dump this
into the same range as other things that are difficult to control or quantify…
Like tinting. Every time you remount a cooler on the IHS, you
are reapplying our best thermal paste – sure we clean it in-between, and it may
look visually as good as new, but on the microscopic level there is leftover
paste/particulate. It could be argued that over time, the IHS interface improves
due to better tinting of the IHS as the result of multiple paste applications
over time. Or it could be argued that it gets worse, from impurities working
their way into the interface and leftover cleaning material. Then there’s
also the way the paste spreads – I’m not sure if you saw the article
Joe C. did on this, but a while back he did some evaluations with multiple
mountings and there’s a lot of variance. All the factors like this, if
I get into them, will make my brain hurt on the amount of variance there could
be from poorly observed and difficult to quantify factors involved in the
testing we do on heatsinks… Yet our testing is fairly reliably reproducible.
I think there are a lot of factors that exist, but just don’t matter
much for the resolution at which we’re measuring.

“You may already be familiar, but if you want to test it you can look
into pressure-x film from sensorprod.com. They give free samples, and if you
pick out the right stuff for sampling (I can help if needed as I figured out
which product version we’d need in the past), it will probably be enough
to do a dozen or more tests without any cost. That should be the easiest way
to quantify the convex nature of a given base and how it affects mounting
pressure across multiple samples. You can analyze the results visually with
a color scale they send you, or if its worth it to you, you can send the samples
in and get some more scientific results ($$$). If you go the free route using
samples, the only cost is time and their sales rep following up with you a
dozen times or so.”

Matt brought up many pertinent, relevant and informed points, but he lacked
enough experience or fine measurement tools (like us), to provide real clarity
on the particular issue of whether a convex base heatsink can deform a CPU IHS
to a more concave shape.

Another heatsink rep confirmed the claim, however:

“Sorry to give you headaches, Mike, but yes, this is a real issue
and we have reproduced it with heatsinks from Thermalright and other brands
that use convex bases.

“It’s true that most Thermalright heatsinks have convex bases, but
this is extremely difficult to control in production, so they vary from almost
flat to extremely convex. For obvious reasons, the issue is more likely to
occur the more convex the base is and the higher the mounting pressure gets.
Some coolers (from TR and other vendors) feature mounting mechanisms that
apply pressure well beyond sane levels (or at least allow to do so). This
way, you’re also more likely to run into said issue.

“By our testing, the implication is exactly as you’ve said, namely that
flat coolers will no longer produce good results on the CPU in question. Once
it is deformed, a flat base heatsink will struggle to keep up with a convex
base one even if it is thermally more efficient.”

Both of the heatsink reps cited above are individuals I’ve known, worked with
and respected for many years, for their technical knowhow as well as their personal
integrity. I doubt greatly that they would feed me bad or misleading information
deliberately.

Sifting through their words and considering my own experience with heatsink
testing over the past dozen years, I came to accept that some level of IHS deformation
probably occurred during our extensive testing with convex base heatsinks, especially
the ones that provide a hefty screw over the center of the base to increase
contact pressure. How much deformation is hard to assess, but knowing that the
difference between a top performer and a middling performer is just a few degrees,
my educated guess was that the drop in performance for a flat base heatsink
(as a result of the extra IHS concavity) would be no more than about 2°C.
(The second rep’s comment, “…no longer produce good results…,”
seems like an exaggeration, especially against the comment of the first rep,
“slight loss of performance.”)

Now the issues were:

1. Our CPU is probably more concave now than the typical CPU used by our audiences.
   Most people don’t subject their CPUs to multiple torture tests with 30+ heatsinks
   over a 3+ year period. So if it is atypically concave, it might now be providing
   worse results for all heatsinks that don’t have convex bases.
2. How much worse, for a flat base heatsink?
3. The question of how much worse the concave IHS CPU is making concave or
   wavy base heatsink perform doesn’t matter; they’re never going to perform
   well without at least a flat base.

Could question #2 be answered accurately? Yes, there was one way that it could:
By testing some flat base heatsinks with our CPU as it was… and then again
after lapping our CPU to a higher level of flatness, or at least
so that it is no longer concave.

LAPPING THE i7-965 EXTREME

Lapping is the popular term for sanding either the base of a heatsink or the
IHS of a CPU to be flatter and smoother. The goal is to achieve closer mechanical
mating between the CPU and the heatsink base for improved heat transfer, leading
to better cooling. The recommended procedure is to lap both CPU and heatsink
base for best results. Search the web and you’ll find not only lots of detailed
instructions and YouTube videos on how to lap a CPU, but also a wide range of
cooling improvement claims.

I shopped locally for sandpaper of different grades, and ended up finding the
really fine grades at an automotive supply shop. The superfine sandpaper is
apparently used to create ultra-smooth paint finishes. I mostly followed these
guidelines at Overclockers.net, but also referenced many other sources as
well. An unused small double-pane framed window was used as the platform for
the sandpaper.

How our Core i7-965 Extreme looked before lapping. You can see the nicks and scratches collected over the years. Note the greater wear in the corners and edges, which suggests they are raised above the rest of the area. Also note the bevelled and rounded edges around the perimeter: That is normal for an Intel IHS. An AMD CPU, in contrast , has an IHS that is much more square at the edges, usually a sharp corner where the top meets the sides. This profile view of the CPU with a steel straight-edge (the back side with cork lining showing) against the IHS shows contact only at the edges; there is a gap through the middle. The IHS is not exactly concave, which impliers a curve. The edges are raised a bit higher than the center. Curiously, running the straight edge 90 degrees perpendicular showed less of a gap, which suggests the concavity is not consistent. One side of this spare window was used as the sanding platform. The numbers on each piece of sandpaper indicates its grit rating. The brownish streaks are copper bits ground from the IHS. I lapped the CPU slowly & carefully over the course of a day. It was deemed complete when the straight edge consistently showed no gap across the center of the IHS. It was difficult to achieve complete flatness. A steady slow stroke, even pressure, and regular rotation of the CPU was employed. Even so, as the following pictures show, a bit of curvature appeared around the primeter, though it might be more accurate to say it remained. My estimate is that about 85~90% of the center is flat; the perimeter slopes away a tiny bit. Center of the IHS against the straight edge, after completion of lapping. Across the center again, CPU turned 90 dgrees. Image of a 1366 CPU without the IHS. Approximate position of the die beneath the lapped IHS.

THE LAPPED CPU: ANY SKEWING OF TEST RESULTS?

The lapped CPU was installed back in the Asus P6T SE motherboard. Thereafter,
heatsink testing proceeded as usual. That was back around Christmas 2012. So
a year later, is there any indication that heatsink test results have been affected
by the lapping? In other words, have there been any heatsinks that performed
well that might not have done so well before the CPU was lapped? Or Those that
did poorly which might have done better pre-lapping?

A quick look at the curvature of the base of heatsinks tested before January
2012 is one place to start. This table ignores other factors, such as size,
and the quality of the mounting system; it’s just a quick check for correlation
between base profile and cooling performance. The ones with convex bases all
tested well. The concave bases all gave poor results. The flat bases gave mixed
results.

Compare that with cooler tested after lapping:

What is clear is that in general, convex base heatsinks fared well before and
after the CPU was lapped. Concave base heatsinks also fared consistently: They
performed poorly before and after the CPU was lapped. A flat base did
not correlate strongly with good cooling pre-lapping but more so after the lapping.

Let’s examine this further.

1. Flat Conventional Base Heatsinks

One heatsink retested right after the lapping was the Silverstone
Heligon, which performed surprisingly poorly in the original review,
hindered by less-than-ideal contact with the CPU. The base was checked with
our straight edge and it appreared to be mostly flat, neither concave nor
convex. It made better contact with the lapped IHS, and when retested with
a single 14cm reference fan at various speeds, there was a 1-2°C
improvement across the board. This result still did not make the Heligon significantly
more competitive against smaller cheaper coolers, though its passive performance
went another titch beyond the Thermalright Macho. So subtle improvements,
not a dramatic one. Unfortunately, this is the only example of a flat solid
base heatsink that we have in hand that was tested before the lapping.

2. Flat DirectTouch Heatsinks

DirectTouch heatpipe bases can only be flat, due to the nature of their
construction. There are lots of questions around this type of base, including
longevity and flatness, and a limit to how tightly it can be mounted on the
CPU due to the fragility of the exposed heatpipes on the base. Morever, there
is a sense among performance-oriented enthusiasts and traditional heatsink
makers that DirectTouch represents something of a cheat, a cheap short-cut.
But there’s no denying its lower cost yet decent performance. A clear disadvantage
is that most IHSs on most CPUs are a touch concave, and DirectTouch bases
can only be flat, at best. They cannot be made with the subtle degree of convexity
that the top “solid” base heatsinks tend to have. Our lapped CPU
is now flat; hence, it stands to reason that DT heatsinks should now do better
than they did on our test system before the lapping.

The Silverstone Argon 01, 02, and 03 coolers with direct touch bases, all reviewed
this year on our lapped CPU, achieved great results, two of the three getting
Editor’s Choice awards and the third getting a Recommendation. Would they have
done as well pre-lapping? We can’t answer that directly, as there’s no un-lapping
our CPU, but we can take another look at the Enermax
ETS-T40, a fairly large DT cooler similar in overall design which Larry
Lee mentioned in the Silverstone Argon 03/01 review as having been “a dud”.
The ETS-T40 was reviewed on the pre-lapped test platform in mid-2012. We happen
to still have this sample on our shelf, so it was brought out for a repeat test
on the post-lapped CPU.

As Larry mentioned in his original review, “One look at the ETS-T40’s
mounting gear and we’re optimistic. A simple metal frame is assembled around
the socket and a thick bar goes over the base [which is used to clamp the
heatsink to the frame & CPU], a system similar to that employed by Noctua,
Prolimatech, and Thermalright on their high performance coolers.” It
is indeed a sturdy, secure and easy to use mounting system. I was able to mount
the heatsink, and run Prime95 in just 10 minutes, with the stock fan dialed
to 1060 RPM (7V). It was clear immediately that the results were going to be
much better this time around. The full range of tests were done in two hours;
the results are in the table below, compared to the ones obtained previously
on the pre-lapped CPU.

1. DirectTouch base heatsinks will cool our our lapped CPU better than
before it was lapped, when it was somewhat irregularly concave.

2. Such heatsinks will still need very good mounting mechanisms and good
qualities in all other aspects of heatsink design and execution to compete
with the heatsinks with solid bases that have reached the top rankings
at SPCR.

3. A DirectTouch or other flat base heatsink that reviews well at SPCR
now will cool as well for you if your CPU has a relatively flat IHS…
or if you lap your CPU as we did ours.

4. With a CPU that has a concave profile, a flat DT or solid base heatsink
will not cool as well; just how much worse will depend on the degree of
concavity your CPU exhibits. The difference could be as little as a degree
or two, but it could be as much as 5~7°C.

5. Slightly convex based heatsinks that have other critical qood qualities continue to review well on our lapped CPU. It is only one of a handful or critical features needed for high performance, so the simple fact of a convex base cannot assure good performance. But it is noteworthy that almost all heatsinks with convex bases have those other critical features for high performance.

6. Concavity of the IHS may be a less critical factor with smaller CPUs,
like the socket 1150, 1155 or 1156 CPUs. The dimensions of the IHS surface
being smaller, the same degree of curvature leads to a smaller gap between
IHS and heatsink base.

7. Finally, to achieve high performance cooling, you must pay close attention
to your gear, just as we do ours, and be prepared to make adjustments,
change components, experiment, and monitor carefully. Just dropping in
a highly rated cooler does not automatically give you great cooling and
super low noise. It’s less of an art than it used to be, but it still
takes intelligent, informed care.

We will be making only one change to our heatsink rankings: The Enermax ETS-T40
will get a postscript and be introduced to the Recommended or Editor’s Choice
ranks. We may have to make some kind of handicap for flat base heatsinks to
reflect that some users’ CPUs are likely to have slight concavity rather than
perfect flatness. On the other hand, it might be better to make note of this
issue whenever we encounter a high performance flat base heatsink. Yes, it’s
another minor headache we’ll deal with in the near future. Meanwhile, rest assured
SPCR keeps trying our best to stay consistent and accurate in all of our
real-world reviews.

LOOKING AHEAD

One comment made by the second of our two heatsink reps was that lapping makes
the IHS thinner and weaker, so it could become subject to further deformation.
I was aware of this opinion before lapping, but weighed the pros and cons and
decided there was too much to be learned and gained. A year of testing after
the lapping, our i7-965E CPU shows no sign of having become concave again. We’re
also not aware of any new records having been set for cooling in this past year,
which might be indicated if the thinner IHS lead to improved cooling.

We’re not certain what other factors will come into play for our heatsink testing
program in the future. Everything wears, and certainly, the socket 1366 platform
is already defunct, so it may be time to make another transition to a newer
test platform before our current system breaks. Unfortunately, we do not have
a new replacement board or CPU waiting in storage this time. A quick look through
Newegg shows only server dual-socket boards available for LGA1366. So we are
already in the hunt for a newer test platform, just in case. In the meanwhile,
we will continue reviewing heatsinks as before, and add cautionary comments
whenever we run into a heatsink with a flat base. This is unlikely to please
everybody, but as the old song goes, you gotta please yourself.

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Articles of Related Interest
SPCR’s 2010 CPU Heatsink
Test Platform
SPCR’s Updated 2012 Small CPU Heatsink
Test Platform

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Discuss this article in the SPCR forums.