tim reliabilty testing

Reliability Tests Of Thermal Interface Materials

High power/voltage IGBT mod­ules with SiC and GaN dies are wide­ly adopt­ed by pow­er invert­er man­u­fac­tur­ers, allow­ing for high­er switch­ing speeds to improve ener­gy effi­cien­cy and bat­tery range for EVs. The increas­ing pow­er den­si­ty in the design neces­si­tates supe­ri­or ther­mal man­age­ment solu­tions, where ther­mal inter­face mate­ri­als (TIM) play a key role in ensur­ing long-term reli­a­bil­i­ty and sta­ble performance.

In invert­ers, 50% of the total ther­mal resis­tance is com­ing from the inter­face between IGBT mod­ules and heatsink, where ther­mal inter­face mate­r­i­al is applied. Hence It is essen­tial to min­i­mize the TIM resis­tance while main­tain­ing long-term reli­a­bil­i­ty under high pow­er and switch fre­quen­cy conditions. 

The key con­sid­er­a­tions of Ther­mal inter­face mate­r­i­al selec­tion can be rough­ly out­lined as follows:

Excel­lent Ther­mal Performance

  • Low ther­mal resis­tance down to 0.04 ˚C·cm2/W
  • High ther­mal con­duc­tiv­i­ty (up to 8 W/mK)
  • Opti­mal Sur­face Wet­ting & Low Con­tact resistance
  • Great con­forma­bil­i­ty to fill up micro­scop­ic voids and cavities

High Reli­a­bil­i­ty and Long-life

  • No bleed-out, pump-out, and flow-out issues
  • No aging effects includ­ing dry-out over time and degrad­ed ther­mal performance 
  • Sta­ble ther­mal imped­ance across accel­er­at­ed aging test


  • Easy assem­bly & broad process window
  • High yield with low/zero mate­r­i­al waste
  • Pad and paste form factor

Phase change mate­ri­als, specif­i­cal­ly, excel at those require­ments and become the most pop­u­lar TIM prod­uct for the pow­er mod­ules appli­ca­tion. They adopt a non-sil­i­cone-based poly­mer matrix with steric struc­ture and chem­i­cal bonds with fillers, which lim­its filler migra­tion and large­ly reduces the risk of mate­r­i­al mobil­i­ty issues like pump out. Addi­tion­al­ly, they go through phase change with a dra­mat­ic vis­cos­i­ty drop at tem­per­a­tures above 45°C. This helps to wet the con­tact sur­face, fill the mini gaps, squeeze out the air voids between the heatsink and heat source, and ulti­mate­ly achieve a very low ther­mal impedance. 

Reliability test types

Besides ther­mal imped­ance and bond line thick­ness, the per­for­mance of those reli­a­bil­i­ty tests is the key cri­te­ri­on when select­ing PCM prod­ucts for invert­er man­u­fac­tur­ers. The typ­i­cal reli­a­bil­i­ty tests that PCM needs to go through for pow­er mod­ule appli­ca­tions are:

(1) High-tem­per­a­ture baking 

  • Test stan­dard: JESD22-A103 
  • Test con­di­tions: 1000hrs @150°C

Objec­tive: Accel­er­ate changes in TIM’s mate­r­i­al and per­for­mance char­ac­ter­is­tics rel­a­tive to pro­longed and ele­vat­ed temperature

(2) 85°C & 85%RH dou­ble 85 tests 

  • Test Stan­dard: IEC 61215
  • Test con­di­tions: 85°C, 85%RH, 1000 hrs

Objec­tive: Accel­er­ate the cor­ro­sive impact of high humid­i­ty and tem­per­a­ture on the ther­mal per­for­mance of the test structure

(3) High­ly-accel­er­at­ed stress test 

  • Test stan­dard: JESD22-A110‑B
  • Test con­di­tions: 130°C, 85%RH, 96 hrs

Objec­tive: Accel­er­ate the cor­ro­sive impact of high humid­i­ty and tem­per­a­ture on the ther­mal per­for­mance of the test structure

(4) Tem­per­a­ture cycling test 

  • Test Stan­dard: JESD22-A104C
  • Test con­di­tion: ‑55 °C to 125 °C (TCB), 1000 cycles

Objec­tive: Deter­mine the resis­tance of TIM to extremes of high and low tem­per­a­tures, and its abil­i­ty to with­stand cycli­cal stresses 

Ther­mal cycling and stor­age tests are more of a tem­per­a­ture and mechan­i­cal stress con­cern. High-tem­per­a­ture stor­age tests pro­vide infor­ma­tion about how the com­po­nents will per­form under long-term high-tem­per­a­ture con­di­tions. Ther­mal cycling tests pro­vide infor­ma­tion about how the com­po­nents will per­form under con­di­tions of repeat­ed tem­per­a­ture changes.

HAST and dou­ble 85 also include humid­i­ty fac­tors. Dou­ble 85 tests are typ­i­cal­ly used to eval­u­ate the long-term reli­a­bil­i­ty of elec­tron­ic com­po­nents under nor­mal oper­at­ing con­di­tions. HAST tests, on the oth­er hand, are used to eval­u­ate the reli­a­bil­i­ty of elec­tron­ic com­po­nents under extreme con­di­tions, such as those that may be encoun­tered in extreme envi­ron­ments or dur­ing trans­porta­tion. The stress lev­el on the com­po­nent dur­ing the HAST test is high­er than dur­ing the Dou­ble 85 tests.

Although the test con­di­tions dif­fer from each oth­er to sim­u­late var­i­ous oper­at­ing and envi­ron­men­tal stress for devices, the mech­a­nism of PCM fail­ure is sim­i­lar. Please see our blog arti­cle Phase Change Mate­r­i­al Fail­ure Mech­a­nism In Reli­a­bil­i­ty Tests

Hon­ey­well PTM7950 is one of the most suc­cess­ful TIM prod­ucts used in high-pow­er invert­ers and high-per­for­mance com­put­ing devices. Ultra-low ther­mal imped­ance with min­i­mum achiev­able BLT and supe­ri­or long-term reli­a­bil­i­ty make PTM7950 stand out from the com­pe­ti­tion as can be seen in the PTM7950 Reli­a­bil­i­ty Report.

Hon­ey­well PTM7XXX series also offers sta­bil­i­ty among ver­ti­cal appli­ca­tions, pass­es auto­mo­tive stan­dard vibra­tion tests, and is cur­rent­ly wide­ly used in auto­mo­tive appli­ca­tions such as pow­er invert­ers.

Are you inter­est­ed in learn­ing more about Pow­er mod­ule ther­mal inter­face mate­ri­als? Con­tact us and one of our Sales engi­neers will get back to you as soon as possible.

About George Kountardas

George is a Jack of all trades with an unappeasable inquiring mind. Obsessed with new products and technologies, he is always pushing forward for better, faster and more efficient applications. Always learning something new.

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