Advancements in Thermal Management at PCB Level for Electronics Design and Fabrication

Transcription

1 Advancements in Thermal Management at PCB Level for Electronics Design and Fabrication Presented By: Pratish Patel Electronic Interconnect 1

2 Table of Content Challenges of the Electronics CFD Analysis under Natural Convection between FR4 and MCPCB. Design Guidelines Fabrication Guidelines Question and Comments. 2

3 Challenges of the Electronics The electronics Industry today is facing challenges such as HOT SPOT CTE mismatch, solder joint stress, thermal fatigue failure shock and vibration issues, SMALLER, FASTER, STRONGER 3

4 Challenges of the Thermal Management Improve thermal performance for reduced junction temps Heat sink design with optimized performance to weight ratios Increase color quality and light output Increase product lifespan Increase energy efficiency Save material cost by optimizing material usage Decrease UL failures with better designs the first time Eliminate color shift 4

5 Case Study A comparative study between FR4 and other PCB s using CFD Analysis under Natural Convection. 5 5

6 OBJECTIVE To conduct a comparative study between FR4 and other PCB s using CFD Analysis under Natural Convection. Four separate boards (FR4, Laird s Metal clad1ka) with different thermal conductivities were modeled. Two different heat sources were provided to each LED (0.06 W & 0.2 W). 48 LED s were populated on each PCB. Two heat sink designs were proposed for each LED wattage type (0.06 W & 0.2 W). The ambient temperature for each model was 25 0 C. 6

7 OUTLINE Thermal Model Layout Simplified Thermal Model Thermal Analysis 1: - Four different PCB s (LED = 0.06 W) Thermal Analysis 2: - Heat Sink Design for eight PCB s (LED = 0.06 W) Thermal Analysis 3: - Four different PCB s (LED = 0. 2 W) Thermal Analysis 4: - Heat Sink Design for Four PCB s (LED = 0.2 W) Results & Conclusion 7

8 Thermal Model Layout Copper (k=380 W/m-K; t = 2 oz or 0.03 mm) PCB (variable k & t values) AL5052 (k=132 W/m-K; t = 1.5 mm) FR4, 1KA, LLD, HTD, MP, NRA-8, TCB-2 & 92ML The thermal conductivities and thicknesses of each layer is provided above. PCB thickness and thermal conductivity was variable in each model. 8

9 Simplified Thermal Model The thermal model was simplified to acquire the satisfactory results. In natural convection, radiation has a very important role in heat transfer. The size of each LED was 0.25 mm 0.64 mm and the minimum radiation surface tolerance acceptable by CFD tool (Flotherm) was 1mm (due to computer hardware limitations), therefore, a single heat source was created to incorporate the effect of radiation. 48 LED s were modeled as single heat source with total wattage of = 2.88 W & = 9.60 W Single Heat Source (LED) 9

10 Thermal Analysis 1: PCBs with LED of 0.06 W 10

11 Thermal Analysis 1 Data Table I PCB with LED Wattage of 0.06 W Boards FR4 1KA LLD HTD Thickness (mm) Thermal Conductivity (W/m-K) LED Max Temp ( C) Thermal Gradient ( C)

12 Thermal Analysis 1 - FR4 Board Temp Profile 8 LED Max Temp = 95.7 O C 12

13 Thermal Analysis 1-1KA Board Temp Profile LED Max Temp = 92.7 C 13

14 Thermal Analysis 2: PCBs + Heat Sink with LED of 0.06 W 14

15 Thermal Analysis 2 Data Table II PCB with Heat Sink for LED Wattage of 0.06 W Boards FR4 1KA LLD HTD Thickness (mm) Thermal Conductivity (W/m-K) LED Max Temp ( C) Thermal Gradient ( C)

16 Thermal Analysis 2 - FR4 Board Temp Profile LED Max Temp = 70.5 C 16

18 Thermal Analysis 2 - Heat Sink Design Dimensions = mm Base Thickness = 3.0 mm Fin Thickness = 1.0 mm # Fins = mm 18

19 Thermal Analysis 3 : PCBs with LED Wattage of 0.2 W 19

20 Thermal Analysis 3 Data Table III PCB with LED Wattage of 0.2 W Boards FR4 1KA LLD HTD Thickness (mm) Thermal Conductivity (W/m-K) LED Max Temp ( C) Thermal Gradient ( C)

21 Thermal Analysis 3 - FR4 Board Temp Profile LED Max Temp = C 21

22 Thermal Analysis 3-1KA Board Temp Profile LED Max Temp = C 22

23 Thermal Analysis 4: PCBs + Heat Sink with LED 0.2 W 23

24 Thermal Analysis 4 Data 26 Table IV PCB with Heat Sink for LED Wattage of 0.2 W Boards FR4 1KA LLD HTD Thickness (mm) Thermal Conductivity (W/m-K) LED Max Temp ( C) Thermal Gradient ( C)

25 Thermal Analysis 4 - FR4 Board Temp Profile LED Max Temp = 75.0 C 25

27 Thermal Analysis 4 - Heat Sink Design Dimensions = mm 28.0 mm Base Thickness = 3.0 mm Fin Thickness = 1.0 mm # Fins = 12 27

28 Results & Conclusion Table V Thermal Analysis Data - LED Max Temp with Heat Sink Set FR4 1KA LLD HTD MP NRA-8 TCB-2 92ML Note Thickness (mm) Thermal Conductivity (W/m-K) LED Max Temp ( C) For 0.06 W LED & Heat Sink LED Max Temp ( C) For 0.2 W LED & Heat Sink 28

29 Note: This thermal analysis is for the comparative study and not to consider the absolute LED temps. The absolute temps will be based on the actual boundary conditions. USA: Europe: Asia: 29

30 Case Study: Lamp with 6 High power LEDs 30

31 Case Study: Lamp with 6 High power LEDs cont. 31

32 Case Study: Lamp with 6 High power LEDs cont. 32

33 Thermal Profile FR4 & IMPCB 33

34 CASE STUDY Thermal at 40W, ST10 NATURAL CONVECTION 40Watt Customer Quote: ST10 represented a 12% to 15% temperature reduction compared to FR4 dt between ST325 and ST10 PCBs are very close to each other FR4 PCB STABLCOR ST10+FR4 40Watt, Natural Convection, STABLCOR PCB running 11.2 o C Cooler Courtesy: CONTINENTAL Automotive France SAS, Mr. Loic Bertrand 34 Technology Presentation-0508

35 DESIGN GUIDELINES DESIGN GUIDELINES 35

36 Types of Thermal management Material? Thermal Interface material bonded on Metal base plate or Carbon Core A thermally & Electrically Conductive Composite Material It has very good In-plane Thermal Conductivity It can be used as a plane layer, Preferably GND plane 36

37 BASE MATERIALS BASE MATERIALS Thermal Conductivity (W/m.K) CTE (ppm/c) Tensile Modulus (Msi) Density (g/cc) FR-4/E-glass 0.3 to to to Polyimide/E-glass 0.2 to to to Copper to CIC (Copper-Invar-Copper) to Aluminum Carbon Composite 2*~ 75* ~4.5 to 7 ~ to 1.7 * Theoretical calculated In-Plane values based on volume & Thermal conductivity of the composite materials 37

38 Additional Materials Material CTE (ppm/k) Thermal Conductivity (W/m.K) FR Stainless Steel % Alumina Ceramic Aluminum (3003/6061) Copper

39 Thickness and Resistivity of Std Weight Copper Weight Thickness 20 C 130 C 0.5 oz mohm/sq mohm/sq. 1.0 oz mohm/sq mohm/sq. 2.0 oz mohm/sq mohm/sq. 3.0 oz mohm/sq mohm/sq. 4.0 oz mohm/sq mohm/sq. 6.0 oz mohm/sq mohm/sq 39

40 Line Width & Edge-to-Edge Spacing Copper Wt. 0.5 oz 1 oz 2 oz. 3 oz. 4 oz. 6 oz. Minimum Line width Minimum Line spacing Prefered Min. Line width The etched copper foil tolerance is typically +/-20% of the foil thickness. 40

41 T-Preg Properties PROPERTIES T-preg Thermal Conductivity, W / m o C 2 ~4 Dielectric Strength, V / mil 1,500 ~ 800 Dielectric Constant, Dk 4.2 ~ 4.8 Peel Strength, pli 6~6.5 Flammability Class 94V-0 Operating Temperature, o C 130~150 41

42 Fabrication Guidelines 42

43 T-preg BASIC CONSTRUCTION MATERIALS T-preg DSL Copper Foil Base Metal /Carbon Composite Material 43

44 Basic Construction T-Preg Thermally Conductive Dielectric/ Prepreg DSL Double Sided Laminate IMPCB s Insulated Metal Printed Circuit Boards 44

45 Single Sided Board T-preg Copper Foil Base Metal Material One or Multiple Layers of T-preg Copper weight 1 to 6 ounces Dielectric layers 4,6 or 8 mil Base Metal Copper or Aluminum 10 to 120 mil 45

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47 FR - 4 Hybrid IMPCB with FR-4/T-Preg PTH & Thermal Vias Mounting Hole Metal Base T-preg Construction Materials FR-4-Double-Sided PCB ( Min ) Metal Base Thermal Vias (0.025 ) 47

48 Two-Layers PTH & Thermal Vias T-lam DSL T-preg Metal Base Mounting Hole Construction Materials DSL internal copper weight up to 4 oz. T-Preg Metal Base 48

49 Construction Materials: DS Outer copper weight up to 4 oz. Thermal Interface material from 4 mil Metal Base

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52 Multilayer Metal Base PTH & Thermal Vias T-lam DSL & T- preg Construction Materials Mounting Hole Buried Vias DSL Copper Foil T-Preg Metal Base 52

53 Double-Sided Metal Core T-preg Metal Core Mounting Hole PTH Construction Materials Copper Foil T-preg Metal-Core 53

54 Multilayer FR-4/T-preg Hybrid FR- 4 Multilayer Board T-preg Buried Via Construction Materials 4 layer FR4 PCB T-preg PTH PTH & Blind Thermal Vias Mounting Hole 54

55 APPLICATIONS 55

56 High Power LED Lighting 56

57 57

58 Junction Block (Relay Box) Headlight Electric drive unit (DC-DC Convertor & EPS Convertor) 58

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60 DC / DC Converters Thermal Vias TTC TCP Metal Base Mounting Hole 60

61 Electric Motor Controls 61

62 Fabrication Guidelines Electrical & Thermal vias Maximum Current Rating vias Thermal Guide for performance 62

63 Electrical & Thermal Vias Vias drilled prior to the Lamination. Min. via drill and Base metal drill 0.040, Min clearance /side. Vias wall design to carry heat & current Not exceeding 2 holes with a diameter, per sq inch and a max copper core thickness. Drill clearance holes in copper core.030 to.040 larger than drill size of the vias. The goal is to have a.015 to.020 ring of T-preg to isolate the via from the copper core. PTH: Min to Max. 63

64 Maximum Current rating for vias Vias Size Wall Thickness Foil Thickness Dielectric Thickness Maximum current of vias is limited by the maximum vias temperature 64

65 Thermal Guide for Performance Function of: Via size Via Wall Thickness Foil Thickness Dielectric Thickness Via pitch Maximum base plate temperature 65

66 Copper to Edge Clearance 7mils to 10mils for Routed Edge 15mils to 20mils for Scored Edge 66

67 15mils+ per side We recommend not exceeding 2 holes with a diameter, per sq inch and a maximum copper core thickness. Drill clearance holes in copper core.030 to.040 larger than drill size of the vias. The goal is to have a.015 to.020 ring of T-preg to 67 isolate the via from the copper core. PTH: Min to 0.125

68 Surface Preparations Exposed Copper Surface Solder Resist Solder coating Coat with Antioxidant to extend T-lam life Used for Aluminum ultrasonic wire bonding Protect lines from Mechanical or Environmental damage and contaminations For Heavy copper conformal coating or potting compound can be applied Standard Hot-Air Leveling for good wetting and provides a thin and uniform solder coating. 300 micro-inches thickness 68

69 Surface Preparations (continue) Plating Reduces Oxidations, mechanical protection, improves solder and wire bonding operations. Nickel, Silver, Gold, Tin, OSP are common Nickel (Electroless) ENIG Silver (Electroless) Use for Soldering and wire bonding micro-inches Slow oxidation rate but difficult to see and remove Plate with 7-12% phosphorous content Electroless Nickel Immersion Gold process Gold thickness 8-10 micro-inches, eliminate porosity Gold thickness micro-inches for Wire bonding Silver thickness 8-10 micro-inches, eliminate porosity Slow Oxidation rate but can be seen 69

70 FABRICATION TOLERANCES GUIDELINES Camber or flatness Milling/CNC or Scoring +/ per inch Punching +/ per inch Cost advantage at Low volume High volume Fix cost No Tooling cost High Tooling cost Finish Clean Edges Burr on edges Substract to subtract +/ / Maximum burr Corner Radius (outside (min) t Minimum Panel Border

71 FABRICATION GUIDELINES Milling/CNC or Scoring Punching Corner radius (inside, min.) 0.7t 0.7t Bridge, Edge to Hole (min) 0.5t 1.5t Hole Diameter (min) 0.2t 1.0t Hole Tolerance. +/ / Hole Location, Hole to holes Hole Location, hole to edge Wire bonding High current application yes Less cost than FR4 71

72 Fabrication Check List Specify Materials in Metal core; Comapny name and part #. Thickness of dielectric. Tg or Td Metal Core Insulation resistance & Thermal conductivity values. 72

73 Fabrication Check List Footprints OR Data sheets Net List Material specifications Construction Details Layout Guideline Mechanical Details Other specific requirements 73

74 CONCLUSION Reduces Hot Spot PCB acts as a Heat Sink Reduces Thermal Stress on Components Operates Cooler SS or DS with SMT NO need to change the Design 74

75 Acknowledgements Thanks to following contributors: Laird Technology Stabcor Inc. for their Stabcor laminates 75

76 Thank You Presented By: Pratish Patel Electronic Interconnect 76