Electronics Forecast: Hot and Getting Hotter Phase Change Thermal Interface Materials (PCTIM) in High Power Electronics Applications

Transcription

1 Electronics Forecast: Hot and Getting Hotter Phase Change Thermal Interface Materials (PCTIM) in High Power Electronics Applications SMTA Midwest Expo Oliver Chu

2 Overview TIM2 Background Evolution of Phase Change Phase Change Advantages Consumer vs. High Power Application Printability Customization Lateral Heat Flow After Power-up Reliability Tests Slide 2

3 Introduction Slide 3

4 Thermal Failure Slide 4

5 Why use a TIM? All hard surfaces in contact with each other form many air pockets due to surface roughness and waviness Goal: Eliminate air and maximize thermal conductivity between two surfaces. Slide 5

6 Functions of a TIM Replace air with solid or liquid Best results obtained with surface fully wetted, eliminating air in all gaps Increase thermal conductivity Thermal conductivity of air is C TIM thermal conductivity is at least 0.5 W/mK (20x higher!) Enhanced TIM materials can be substantially higher Minimize thermal resistance Optimize processing for continuous interface Maximize wetting to different surfaces Slide 6

7 Types of TIM Thermal Performance Adhesion Gap Filling Rework Reliability Grease X O O Phase Change X O Adhesives O O X Films O X O O Gap Fillers O O = Good O= OK X= Poor Slide 7

8 Evolution of Phase Change Materials Applicator Format Alternative for thermal grease Films Phase change coated substrate Offered custom preforms Dispensable Fast drying paste for precise application Printable Uniform thickness Complete design flexibility and control Slide 8 Once dried all yield the same thermal performance.

9 Phase Change Advantages Flexibility with thickness and geometries Optimum thermal contact, bondline even at low pressure Increase of semiconductor efficiencies Pre-application without preheating Optimum contact before first warm-up Non-silicone, eliminates pump-out Material expands by 15-20% in volume during phase change Damage-free reworkability Slide 9

10 Current Applications for Phase Change Consumer Notebook computers Gaming consoles Smartphones AiO PC s LED applications Memory modules TEC modules Heatsinks and heatpipes High Power IGBT Modules DC-DC Converters Transportation Telecommunications Base stations Other power electronics customers Slide 10

11 CPU vs. IGBT CPU IGBT Chip Area (mm 2 ) Power Density (W/cm 2 ) Force Applied to heat sink Several Newton Several kilo Newton Thermal Cycling demand None Large Expected Power Cycles None > 100,000 Expected Lifetime (years) < Cost of Replacement (US$) < 200 1, ,000 Ambient Temperature ( C) Case Temperature ( C) < Slide 11

12 IGBT Design Slide 12

13 Stencil Printing Roll: The circular motion of the paste as it moves across the stencil Squeegee Compound Paste Drop-off: The tendency for the paste to fall off the squeegee blade after printing Paste Bead Paste Curtain Slide 13

14 Stencil Printing Key machine settings: Print speed: 15 mm/s Print 100 N (across a 30 cm long squeegee) Release speed: Slowest possible on machine Test 1: Printing Patterns (7 mm ) of twenty printings without pause or cleaning of the underside of the stencil to establish print stability Test 2: Printing of 1 PCB, leave for a determined period of time (0.5h, 1hr, 2hrs) and print a second PCB to establish material abandon time. 7 mm Slide 14

15 Print Patterns Print only where Compound is needed As thin as possible As thick as required Each application should have it s own custom print pattern Slide 15

16 Stencil Printing Results Adequate printing was achieved with standard stencil printers used for solder paste (MPM) More than 20 consistent prints without a requirement for stencil cleaning is adequate for most printing applications An abandon time of two hours is acceptable for mass production Negligible reduction in printed material is seen during the 20 printings The relatively high viscosity requires adequate print pressure, slow print speeds, slow withdrawal of the substrate from the stencil Dried and after mounting the compound shows a good lateral flow and distribution at heat up above phase change temperature Process can easily be automated for mass production with consistent results Slide 16

17 Phase Change Technology Step 1 Slide 17

18 Phase Change Technology Step 2 Slide 18

19 Phase Change Technology Step 3 Slide 19

20 Phase Change Technology Step 4 Slide 20

21 Lateral Heat Flow at Power-up 65 C Uniform Layer Slide 21

22 Pressure vs. Rth- Characteristics Current phase change film Novel phase change film Thermal grease Rth [ C-inch²/W] N/cm² Novel phase change material allows for lower mounting pressures. Slide 22

23 Long-therm Stability at 125 C (Open Bake) R th [ C/W] T [h] No degradation seen after 1000 hours. Slide 23

24 Thermal Cycling -40 to +150 C -40 to 150C No pump-out observed after 1750 cycles. Slide 24

25 Vertical Stability 20 mm x 20 mm Thixotropic properties: After C Material remains stable, no changes in dimension 25 mm x 25 mm Slide 25

26 Removeability Slide 26

27 Summary Printable phase change materials offer increased flexibility and optimization options. The phase change exhibits excellent resistance to pump-out. Thermal performance of printable phase change material is comparable to dispense and film formats. Phase change materials meet the high temperature and high reliability requirements of high power applications. Slide 27

28 Thank you!