Roundup with 5 phase change pads: Honeywell PTM7950, PTM7950SP, OEM PCM5000, PCM8500 and Thermalright Heilos Review

1 - Introduction an product overview 2 - Test methods and equipment 3 - Thermal resistance, mimal bondline thickness 4 - Thermal conductivity, CPU and GPU simulations 5 - Microscopy and laser-induced breakdown spectroscopy 6 - Summary and conclusion

Today we are going to take a close look at five different phase transition pads and add them to the upcoming database. With the two PCM5000 and PCM8500, I am also testing two OEM pads with a thickness of 0.2 mm, which are sometimes cheekily sold as Honeywell (AliExpress, eBay), but are pure OEM products from a third-party supplier and as such are legally included in many labeled products. In addition to the Honeywell PTM7950 already tested, there is also the Honeywell PTM7950SP as a very viscous paste, which is also advertised as a PTM. The Thermalright Heilos completes today’s quintet, as a real gelid pad with a validatable origin was unfortunately not available by the deadline.

Phase Change Material (PCM) or Phase Transition Material (PTM)?

Phase Change Materials (PCM) are materials that can change their physical phase (e.g. solid, liquid, gaseous) at a certain temperature, thereby storing or releasing large amounts of thermal energy. They are mainly used for temperature control and energy storage, e.g. to prevent overheating in electronic devices and batteries. During the phase transition (e.g. from solid to liquid), the PCM absorbs or releases a considerable amount of latent heat without the temperature of the material changing significantly. For those who are not yet familiar with this, here’s a practical example: there are these great pocket warmers that can be bent in the winder in the solid state so that they then release the energy previously stored during heating from the liquid to the solid state. It is therefore a kind of latent heat accumulator. It is sometimes incorrectly stated that PCM is better as a heat conducting pad because it can initially store the heat and use it for the phase transition, but this is completely wrong.

Phase transition materials (PTMs), on the other hand, are materials that undergo phase transitions between different structural or electronic states. The phase transition in PTMs leads to a change in the physical or chemical structure of the material, which influences its properties in a targeted manner. But this is exactly what we actually need as a heat conducting pad! In PCMs we find the classic phase transition between classic aggregate states (solid, liquid), in PTMs the phase transition between different structural states. Or, to put it in a nutshell: PCM is used to absorb or release latent heat, PTM utilizes the change in physical properties without significant heat aspects. So let’s agree on the term PTM, even if some suppliers have not yet internalized this.

Honeywell PTM7950

Many manufacturers have been experimenting with the Honeywell PTM7950 thermal pad and graphene pads on graphics cards for some time now. With good success, as demonstrated above all by AMD board partners (and AMD on the MBA cards) or MSI. Paste or no paste, the load on graphics cards in particular is far too heavy a burden for many normal pastes in the long term. In addition to the horizontal forces caused by the very different expansion coefficients of the chip and heatsink (which is why, for example, 1000 cycles are tested), it is above all the higher temperatures and direct contact with the substrate without an extra heatspreader that are important here. Ageing effects such as pump-out, drying out and simple chemical degradation are not something that today’s GPUs really like in the long term. In addition to the 0.25 mm thick pad, you also get a couple of adhesive aids for applying smaller sections, which is really helpful (especially the 1 cm x 1 cm on the TIMA5 are very fiddly). The pad was neatly packaged in a durable box.

Honeywell PTM7950SP

This PTM paste is actually a hybrid, because on the one hand it is a very viscous paste and on the other hand it has the properties of a phase transition material (PTM). The advantage lies in the slightly better filling of unevenness and gaps, where the 0.25 mm thin pad already fails, but the thermal resistance is somewhat higher and you really have to have skills when applying it. For the rest, what has already been said about the PTM7950 applies. But I’m curious to see whether it will be a viable alternative.

Incidentally, the origin is interesting here. A Shenzhen Esamconn Electronics Co., Ltd. is listed as the “producer”, but based on various searches, it is purely a reseller of all sorts of things and does not manufacture anything itself. So either this PTM paste is an extremely successful counterfeit, or the original has been bottled and sold, although based on the properties measured and the chemical composition, I would rather guess the original. But either way, it is representative, but of course I have to mention it. The accessories look very extensive with spatulas, screwdrivers and brushes, but you shouldn’t be dazzled, because you can get all this for less than 10 cents when you buy it.

Thermalright Heilos

This pad is not a Honeywell PTM, but some deviating OEM pad of medium quality. We will see that it does what it is supposed to do, but cannot deliver top performance. This is due to many features, which I will show in detail later. I also don’t want to spoil anything yet. The pad thickness is 0.2 mm, whereby you have to use 175 µm and less, because otherwise there is not enough contact for a clean burn-in. And no, it’s not Helios, as the packaging suggests. Spelling mistake or marketing gag?

PCM5000 OEM and PCM8500 OEM

Technical data

As there are no data sheets worthy of the name except for Honeywell products, we’d better concentrate on the real results, which I don’t want to spoil, so I’ll leave this point out for now. But the real measurement results are just around the corner, so stay curious and keep reading!

Further links and basics