Silicone vs Silicone Free Thermal interface materials

Silicone vs. Silicone-Free Thermal Interface Materials

The devel­op­ment of high fre­quen­cy, speed, pow­er, per­for­mance, and inte­gra­tion of elec­tron­ic devices great­ly increas­es the risk of over­heat­ing prob­lems. That’s why effec­tive ther­mal man­age­ment is extreme­ly impor­tant for var­i­ous elec­tron­ics, and the key objec­tive of ther­mal man­age­ment is to remove excess heat from elec­tron­ic devices to the ambi­ent environment. 

As an advanced mate­ri­als sup­pli­er, CAPLINQ has been meet­ing the appli­ca­tion needs of elec­tron­ic device man­u­fac­tur­ers. We pro­vide vital mate­ri­als for ther­mal man­age­ment solu­tions across mul­ti­ple indus­tries which work close­ly with Honeywell’s Ther­mal Inter­face Mate­ri­als on their ther­mal solu­tion strategy. 

Ther­mal inter­face mate­ri­als (TIMs) play a cru­cial role in man­ag­ing heat dis­si­pa­tion between elec­tron­ic com­po­nents and heat sinks. One key fac­tor in choos­ing a suit­able TIM is the com­po­si­tion of the mate­r­i­al. TIM’s mate­r­i­al com­po­si­tion is depen­dent on the appli­ca­tion and the desired ther­mal con­duc­tiv­i­ty. As new tech­nolo­gies and mate­ri­als are cre­at­ed, the pre­cise for­mu­la­tion and com­po­si­tion of a ther­mal inter­face mate­r­i­al may also change over time.

In recent years, there has been a grow­ing debate about sil­i­cone-free and sil­i­cone-based TIMs. In this arti­cle, we define the char­ac­ter­is­tics, advan­tages, and dis­ad­van­tages of both sil­i­cone-free and sil­i­cone-based TIMs to make an informed deci­sion when select­ing a ther­mal inter­face material.

Silicone-based Thermal Interface materials

Sil­i­cone-based chem­i­cal for­mu­la­tions are wide­ly employed in elec­tron­ic appli­ca­tions due to their enhanc­ing prop­er­ties. Sil­i­cone has sev­er­al fea­tures that make it appro­pri­ate for extreme oper­at­ing con­di­tions, includ­ing the abil­i­ty to cope with vibra­tion, chem­i­cals, and extreme tem­per­a­tures. They are typ­i­cal­ly for­mu­lat­ed using sil­i­cone poly­mers, such as sil­i­cone oils or greas­es, with added fillers for improved ther­mal con­duc­tiv­i­ty. Giv­en these char­ac­ter­is­tics, sil­i­cone is pop­u­lar as the foun­da­tion chem­i­cal for ther­mal inter­face mate­ri­als (TIMs). 

High Ther­mal Con­duc­tiv­i­ty: Sil­i­cone-based TIMs gen­er­al­ly offer high­er ther­mal con­duc­tiv­i­ty of 6–12 W/mK (Honeywell’s Quick Ther­mal Con­duc­tiv­i­ty Overview), enabling effi­cient heat trans­fer across the inter­face. This char­ac­ter­is­tic makes them suit­able for appli­ca­tions with demand­ing ther­mal man­age­ment require­ments such as eMo­bil­i­ty, Pow­er Sys­tems, and LED Light­ing

Excel­lent Com­press­ibil­i­ty: Sil­i­cone-based TIMs often exhib­it bet­ter com­press­ibil­i­ty with high­lights on Hon­ey­well’s Ther­mal Put­ty Pads 90% com­press­ibil­i­ty, allow­ing for effec­tive fill­ing of micro­scop­ic sur­face imper­fec­tions, air gaps, and large dimen­sion vari­a­tions. This ensures opti­mal ther­mal con­tact and improved heat dis­si­pa­tion. We can see in the fig­ures below the Ther­mal Per­for­mance of TGP3510PT in terms of deflec­tion and decreased ther­mal imped­ance in increas­ing pressure.

Nev­er­the­less, there are cer­tain lim­i­ta­tions when using sil­i­cone-based TIMs:

Elec­tri­cal Con­duc­tiv­i­ty: Sil­i­con-based mate­ri­als are elec­tri­cal­ly con­duc­tive at high tem­per­a­tures because sil­i­con elec­trons can break loose from the sil­i­con cova­lent bond. Elec­tri­cal con­duc­tion is enabled by their move­ment across the lat­tice. As a result, cau­tion must be exer­cised to avoid short cir­cuits when employed in appli­ca­tions with exposed elec­tri­cal con­nec­tions or sen­si­tive circuitry. 

Honeywell’s sil­i­cone-based TIMs range from Ther­mal Greas­es, Ther­mal Gap Pads, Ther­mal Put­ty Pads, One-PartTwo-Part Hybrid, and Ther­mal Insu­la­tors with both high ther­mal con­duc­tiv­i­ty and high compressibility.

Silicone-Free Thermal Interface Materials: Efficient Alternatives for Heat Dissipation 

Sil­i­cone-free TIMs are for­mu­la­tions that do not con­tain sil­i­cone com­pounds. Instead, they are typ­i­cal­ly based on non-sil­i­cone poly­mers, such as acrylics, poly­imides, or ceram­ics. Hon­ey­well offers sil­i­cone-free, ther­mal­ly con­duc­tive Phase Change Mate­ri­als (PCM) in both pad and paste for­mats. Based on a robust poly­mer PCM struc­ture, these mate­ri­als exhib­it effec­tive wet­ting prop­er­ties dur­ing typ­i­cal oper­at­ing tem­per­a­ture ranges, result­ing in very low sur­face con­tact resis­tance which makes them desir­able for high-per­for­mance semi­con­duc­tor, and auto­mo­tive appli­ca­tions. These sil­i­cone-free mate­ri­als offer sev­er­al dis­tinct advantages:

Low Out­gassing: With the absence of sil­i­cone, TIMs typ­i­cal­ly exhib­it low­er out­gassing char­ac­ter­is­tics, min­i­miz­ing the risk of con­t­a­m­i­na­tion or degra­da­tion of near­by com­po­nents. This makes Honeywell’s car­bon hydride based PCM impor­tant for high-vac­u­um appli­ca­tions, such as aero­space or semi­con­duc­tor man­u­fac­tur­ing. In the graph below you will see the Out­gassing test­ing of one of Honeywell’s in-demand PCM, the PTM7950. A min­i­mal 0.052% weight loss was observed dur­ing tem­per­a­ture ramp­ing up and 0.060% weight loss was observed when the sam­ple was bak­ing at 200°C for 30 min where­in the weight loss rep­re­sents the volatiles evap­o­rat­ed dur­ing testing.

PTM 7950 TGA Report

% Outgassing for PTM 7950
Fig­ure 2. % Out­gassing for PTM 7950

Elec­tri­cal Insu­la­tion: Non-sil­i­cone poly­mers pos­sess inher­ent­ly high dielec­tric strength, min­i­miz­ing the risk of short cir­cuits between sen­si­tive elec­tron­ic com­po­nents. One exam­ple of non-sil­i­cone TIMs is the study of Demko et. al.: Ther­mal and Mechan­i­cal Prop­er­ties of Elec­tri­cal­ly Insu­lat­ing Ther­mal Inter­face Mate­ri­als. In this paper, a new poly­imide-based ther­mal inter­face mate­r­i­al is intro­duced. A poly­imide film is loaded with inor­gan­ic par­ti­cles in such a way as to increase ther­mal con­duc­tiv­i­ty, pro­duc­ing three grades of TIM films but still main­tain­ing the dielec­tric break­down volt­age (Fig­ure 4).

Thermal Conductivity and breakdown voltage for three grades of polyimide films
Fig­ure 3. Ther­mal Con­duc­tiv­i­ty and break­down volt­age for three grades of poly­imide films

Thin Bond Line Thick­ness (BLT). Honeywell’s Phase change mate­ri­als come in thick­ness­es rang­ing from 0.2–1mm. Those are the ini­tial val­ues that are adjust­ed after you heat up (>45°C) and pres­sure the mate­r­i­al. Their sil­i­cone-free chem­istry enables them to achieve a bond­line of 20~30μm mak­ing it the thinnest, clean­est, and most reli­able bond­line in the market.

How­ev­er, sil­i­cone-free TIMs also have some limitations:

Low­er Ther­mal Con­duc­tiv­i­ty & Com­press­ibil­i­ty: Non-sil­i­cone mate­ri­als have low­er ther­mal con­duc­tiv­i­ty, result­ing in less effi­cient heat trans­fer. They are also less com­press­ible, which makes it dif­fi­cult to achieve opti­mal sur­face con­tact and remove air gaps between the heat source and heat sink. These con­straints can have an impact on over­all ther­mal performance. 

Despite these con­straints, Honeywell’s unique PCM offer ther­mal­ly con­duc­tive TIMs of 6–12 W/mK (PTM7000 | PTM7900 | PTM7950) in both pad and paste formats.

Choos­ing the right ther­mal inter­face mate­r­i­al is crit­i­cal for improv­ing heat dis­si­pa­tion in elec­tron­ic devices so an appli­ca­tion-spe­cif­ic assess­ment should be con­duct­ed. Con­tact us and our appli­ca­tion engi­neers and in-house ther­mal experts will help you out with prod­uct selec­tion for your appli­ca­tion requirements.

About Darlene Pudolin

Darlene Pudolin is one of CAPLINQ's Application Engineers specializes in Thermal Interface Materials, Fine & Specialty Chemicals, and Soldering Materials within the company's Technical Marketing unit. Darlene recently joined CAPLINQ in early 2023 but has been an experienced materials quality engineer for 5+ years. She has a broad range of experience in materials solution from Thermal Interface Materials, Cement Chemistry, and Hydrogen Renewable Technology. With a long history of serving customers in Industrial and Research academe, Darlene is passionate on driving solutions about troubleshooting points that best fit the market requirements. Based in the Philippines, Darlene holds a Bachelor's degree in Chemical Engineering from Mapua University and currently doing her Master's degree in Energy Engineering at University of the Philippines Diliman.

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