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Thermal Interface Liquids vs. Thermal Interface Pads

Once you get yourself firmly down the thermal interface materials rabbit hole, you’ll find yourself comparing liquid dispensed materials against pad-based materials. There is an easy answer, but its only possible in about 30% of applications. That answer is that liquid dispensed options are the overall better choice, for a few reasons. But they just don’t always make sense. We will explore that below. For now, we will start with the benefits of each.

If you are very new to thermal interface materials, its important to note one thing. When we use the word liquid, it conjures images of low viscosity materials that will run all over the place. That’s not the case with most liquid thermal materials. Instead, think of them more like a gel or a paste. The term for this is thixotropic. Since these materials are highly filled with thermally conductive materials, they’ve been described as peanut butter filled with sand. While this isn’t completely accurate, it’s a good way to imagine how they behave, at least in their uncured state. What you will find is that they cure to the same consistency as the pads. You can think of them as customizable thermal pads.

Benefits of Thermal Interface Pads

  1. Low cost of entry. Simply put, you do not have to buy any equipment to apply a thermal pad. Even today, the majority of thermal pads are applied by a human hand (sometimes with the aid of a tweezers). That being said, there are ways to automate. Some companies have developed air suction robotics to pick and place pads in high volume. Additionally, there is a rising trend of placing die-cut pads into tape and reel, for automated feed. This is sometimes called pocket tape.
  2. They come ready to go. While this will be listed as a con as well – you will generally receive thermal pads already die-cut to the exact size you need. Many times they will come cut on a sheet, and can be plucked off and applied. Sometimes they will come loose in a box. Many suppliers will cut them hundreds of different “standard part” sizes. Most of these mirror the popular sizes of MOSFETS.
  3. There is additional process to worry about. With the liquid dispensed options, you are usually wither dealing with a 1-part gel that doesn’t ever really cure. Or you’re dealing with a 2-part system that needs to time to cure in place. While this can be an advantage, its not a set it and forget system like a pad.

Disadvantages of Thermal Interface Pads

  1. Cost of material. There are a couple ways in which using a pad-based product will cost more money overall.
    1. You are paying for the material you don’t use. Even if you buy the parts already die-cut, you are paying for what the die-cutter had to throw away
    2. On a straight material to material basis, pads cost more. This is because the manufacturer’s need to take extra steps to make the rolls, and sheet the material.
  2. Component Stress. This is highlighted in the benefits of liquids, but its worth mentioning twice. While there are now very soft thermal pads, registering in the Shore 00 scale, most are not, and you give up other things to get there. Even with soft materials, there can be some stress on the components your pad will be touching, especially during assembly.

For the hardware engineers, trying to hone in on the exact thig you need for your application. Reach out via the Find the Right TIM tool and we’ll walk through it.

For the PC builders reading this. If you’re going to go with a pad, GELID Solutions makes a solid product, at a reasonable price. You can buy their stuff on quickly on Amazon. Here is a link to one of their thicker GP – Extreme pads.

Benefits of Liquid Dispensed Thermal Interface Materials

  1. Conversely, they are cheap on a material-to-material basis, compared with thermal pads. This is not a hard and fast rule, but you can expect to pay between 10 and 30% less for the liquid solution.
  2. Low assembly stress. Since they go on as a soft, uncured gel of sorts, they put almost no stress on component during assembly.
  3. Enhanced interface. Because they go on in a liquid state, they are better able to fill the small spaces on your application, eliminating more air in the interface. Air is one of the worst enemies of thermal transfer. Because of this, many users get better thermal transfer from liquids, even when they have the same w/mk of a pad solution. This can get confusing, so we recommend reading our learning section on thermal conductivity here.
  4. Versatility and customization. For heavy users of thermal interface materials, the different configurations of pads, and differing materials can lead to a long list for both production and procurement. Settling on one liquid-dispensed material can cut down the BOM quite a bit by allowing for use across several applications.

Disadvantages of Liquid Dispensed Thermal Interface Materials

  1. Dispensing equipment. While it is relatively simple to apply liquid TIMs with low cost hand dispense guns, any kind of mid to high level production is going to call for a dispensing machine. Automation is required for good repeatability. This is a disadvantage when compared with die-cut pad options which can be much more reliably repeatable without automation.
  2. Material settling. Although most suppliers do their very best with the chemistry, in order to avoid this problem, only so much is possible. The more highly filled (meaning more thermally conductive) the material, the worse the problem is. In many cases a program om package turning is needed to avoid the problem. Most supplier will have good recommendations on how to avoid this.

Conclusion

There is no perfect answer when asking this questions. Each thermal interface media have their own pros and cons, and its largely dependent on your application and production. If you can make it work, its normally best to try to use liquid dispensed options, but its not wrong not to.