Heats Sinking for InnoSwitch

Transcription

1 Heats Sinking for InnoSwitch The InnoSwitch Family of ICs combines Primary FET, Secondary SR Driver and Feedback circuits in a single surface-mounted package & can be directly solder at the solder-side of PCB. A direct cooling method by employed a Heats-Spreader (consists of Mylar insulator and metal foil) is a effective means to transfer heats away from the package for cooling. Output Power (85 265Vac) Heats-Spreader is Needed? Relative Housing /Size (External, Inch 3 ) Large Moderate Small 12W NO (1.53 Inch 3 ) NO YES (1-Inch 3 ) 15W NO NO / YES YES 20W NO YES YES (2.73 Inch 3 ) 25W NO (5.50 Inch 3 ) YES YES (2.88 Inch 3 ) Page 1 PI Application team March, (Rev-3)

2 InnoSwitch with Heats-Spreader Facts on Thermal Dynamic 1) Treat the Adapter as an heatsink! (Heat inside adapter is to be extracted to the surface for ventilation. 2) Thermal conductivity varies significantly from materials. Air has lowest K factor. Materials K (W/m ⁰K) Copper 355 Aluminum 175 FR4 PCB 0.25 Solder 65/67 39 * Silicon Adhesive 0.8 Air Reduction of K (poorer heats conductor) Thermal Conductivity Factors 3) Total thermal Impedance/Resistance (θ) is to be kept smallest as possible when varies between L (distance) and K (material). K L Acs Where : a) θ is thermal impedance ( C/W) b) K is the Thermal Conductivity Factor c) L is the thermal path length d) Acs is the cross sectional area where the heat is being applied Page 2

3 2.67mm InnoSwitch with Heats-Spreader The Junction-to-Ambient thermal resistance R θ J-A can be expressed as a sum of thermal resistances. e.g, R θ J-A = R θ Junction-Case + R θ Case-Silicon + R θ Silicon-Mylar + R θ Mylar-GapA + R θ GapA-Copper + R θ Copper-GapB + R θ GapB-Plastic + R θ Plastic-Ambient T Ambient R θ Plastic-Ambient T Plastic R θ GapB-Plastic T Gap2 Total thickness of heats-spreader Plastic Housing (2.0mm) Airgap - B Metallic layer ( mm) Airgap - A Mylar Insulator (0.40mm) Silicon Adhesive ( mm) Area filled with Silicon Adhesive Area filled with Silicon Adhesive R θ Copper-GapB T Copper R θ GapA-Copper T Gap1 R θ Mylar-GapA T Mylar R θ Silicon-Mylar PCB (1mm) Power Dissipated Thermal Resistance Model of an INNOSWITCH assembly with Heats-Spreader T Silicon R θ Case-Silicon T Case R θ Junction-Case Page 3 T Junction

4 InnoSwitch with Heats-Spreader Design Consideration ❸ ❶ ❹ ❶ ❷ ❸ ❸ ❸ Sectional View of InnoSwitch Assembled with Heats-Spreader 1) Areas contributed most to the overall thermal resistance (θ) is Airgap A & Airgap B, this distances is between inner plastic wall and location of InnoSwitch & need to be correctly design so that Heats-Spreader assembly can be tightly fitted to reduce Airgap. 2) The Mylar insulator has high thermal resistance but is not a controllable item. 3) Silicon Adhesive should be sufficiently filled up top and sides (pins) of InnoSwitch for reduced casing thermal resistance. 4) The metallic layer (Copper or Aluminum) is to spread heats away, it thickness and materials could alter surface hot-spot temperature. Copper has a better effect. Page 4

5 InnoSwitch with Heats-Spreader Design Consideration Silicon Adhesive (Completely filled around InnoSwitch) Tight fit between InnoSwitch and outer housing Primary PCB (With InnoSwitch) Heats-Spreader (Aluminum foil) Mylar Insulator Die Substrate of InnoSwitch InnoSwitch s Die Mylar Insulator Heats-Spreader (Aluminum foil) Daughter PCB Page 5 Sectional view of Heats-Spreader Assembly

6 InnoSwitch with Heats-Spreader Benefit (1) Eliminate intermediate heatsink assembly a single Heats-spreader can be sized to cover all heat sources (INNO, SR-FET-SO-8, AC Bridge, etc.,) Auxiliary Heatsink need to contact with the adapter s inner wall Silicon Adhesive Areas Location of heats-spreader Auxiliary Heatsink touch the adapter s inner wall Silicon Adhesive 5V@4.5A (InnSwitch) 5V@3.5A (Discrete Solution Design) Page 6

7 InnoSwitch with Heats-Spreader Benefit (2) Reduce CE or RE emission Some design has added copper foil on PCB side to improve EMI performance. Copper foil at component side has help reduce EMI emission in most designs. Page 7

8 Assembly of Heats-Spreader with InnoSwitch 1) Heat-Spreader is formed by combined of thin sheets of Mylar insulator and heat conductive material like Copper/Aluminum; 2) The insulator sheet (0.43mm) is to be cut to the full size of PCB areas and overlay with a metal foil (as heat-spreader, mm) which will cover only the heated areas include INNOSWITCH and SR-FET. 3) Heat conductive Silicon glues is applied around the devices to be cooled with a predetermine amount. The glues need to fill the space surround the device and the heat-spreader. 4) Warp the Heat-Spreader with the PCB assembly and solder the electrical terminal pin (if available) before insert the completed assembly into the plastic housing. PCB Completed Final Testing Apply Silicon Glues at INNO and SR-FET Apply Heat- Spreader on designated PCB location Hand Solder Ground Terminal (If available) Insert Heat- Spreader Assembly into Housing Page 8

9 Assembly of Heats-Spreader with InnoSwitch ❶ Silicon Adhesive should spread and reach coverage area of heat-spreader. ❷ Silicon Adhesive should completely cover the TOP section of InnoSwitch to fill surfaces roughness. InnoSwitch InnoSwitch (Photo with heat-spreader removed) Design Note : For maximum heat sinking effect, InnoSwitch should be located at the center of heats-spreader. Heats-Spreader Assembly 3mm (approx.) (Height of glues to cover all component leads) (Photo with heat-spreader removed) Page 9

10 Method of Assembly with heat-spread for 5V*4A Silicon Rubber Compound is filled around the InnoSwitch: a) Heats sinking; b) Insulation/seals within HV areas; c) Increase Mechanical Strength of the assembly Mylar Insulation Sheet 0.2 mm Aluminum foil Connected to O/P GND (Optional) Page 10

11 Thermal result for with heat-spreader Aluminum Foil (0.3mm) (Less effective than Copper) Page 11

12 Heat-Spreader Design for Silicon Glues (Min. 15 c.c. is to be applied in these area) 33 mm 28 mm 13 mm (x2) 3.5 mm (x2) 40 mm Insulation Sheet (Materials : Mylar, 0.43mm UL ) 35 mm Heat-Spreader (Materials : 0.3mm Copper Foil) Silicon Glues (Min. 5 c.c. is to be applied in these area) Location of Insulation Sheet & heats-spreader Page 12

13 Thermal Result for 5.5V*4.5A Temperature Rise on 5.5V * 4.5A Demo Components 90Vac input 264Vac Input Copper Foil (0.3mm) Mylar Insulator IC INN2125K (InnoSwitch) SR-FET 98.9 ** 96.5 Transformer - Core Transformer - Winding 96.3 ** 91.8 Outer Case IC s Tab SR- FET InnoSwitch Outer Case SR-FET Ambient Temp Page 13

14 Thermal Result for 24W QC3.0 (Test at worst case 6V/4A) Input:90Vac Input:264Vac Description Temperature( ) Temperature( ) T - Ambient U1 (INN2215K) T1 (Winding) T1 (Core) Q1(SR-MOS) Cout(C7) Cin(EC2) Case (hot spot) Actual Housing (50mm length) Heat Spreader Testing Conditions and Setup : a) Perform under a controlled temperature chamber; b) PCB is being mounted inside an enclosed simulated plastic housing ; c) Thermal coupler (type-k) are attached to respective measuring points; d) Temperature is recorded after 1 hours from initial turn on. Demo setup for temperature test (Thermal coupler had removed) Page 14

15 Page 15 Source and Contact for Silicon Adhesive (Glues for Heat-Spreader)

16 Page 16 Back up slides

17 Page 17

18 InnoSwitch with Heats-Spreader The Junction-to-Ambient thermal resistance R θ J-A can be expressed as a sum of thermal resistances. e.g, R θ J-A = R θ Junction-Case + R θ Case-Silicon + R θ Silicon-Mylar + R θ Mylar-Gap1 + R θ Gap1-Copper + R θ Copper-Gap2 + R θ Gap2-Plastic + R θ Plastic-Ambient Plastic Housing (2.0mm) Airgap - B Metallic layer ( mm) Airgap - A Mylar Insulator (0.40mm) Silicon Adhesive ( mm) Area filled with Silicon Adhesive Power Dissipated Area filled with Silicon Adhesive Total thickness of heats-spreader PCB (1mm) Thermal Resistance Model of an INNOSWITCH assembly with Heats-Spreader Page 18