Seminaari 10.2.2015 PCB Heat Management Prepared by Markku Jämsä Aspocomp Presented by Terho Koivisto Aspocomp
Content of the Presentation PCB cooling solutions Thermal vias Metalback options Embedded Cu coin Benchmark of the options 2
PCB COOLING SOLUTIONS
Basic Strategies of PCB Cooling Spreading and dissipating Cooling through the PCB 4
Cooling Through PCB Need for PCB cooling is coming from some components that create co siderable amount of heat which has to be conducted through the PCB Excess heat can eceed 100W in some cases 5
Thermal Conductivity of Some PCB Materials Material Conductivity W/mK (bulk) Availability in PCB Process FR4 laminate 0,3-0,4 Yes FR4 with fillers 0,3-0,7 Yes Low loss laminates with fillers 0,3-0,9 Yes Thermally conductive laminates 0,7 3,0 Yes Ceramic substrates 26-260 No Copper 330-390 Yes Aluminum 140-230 No SAC solder 50 No Conductive viafill paste (CB100) 3,5 Yes Conductive adhesive (CF3350) 7,0 Yes TIM materials 1-10 No 6
Most Common Tools for Cooling Through the PCB Thermal Viafarm Filled and Capped Via Since 2002 Cu Coin Since 2012 Metalback PCB Since 2004 7
Viafarm
Viafarm, Overplated Thermal Vias Typical construction Typical viafarm case IPC4761 Type VII Plug&Plate Capped Via Overplated Thermal Via Filled and Capped Via VIPPO Via In Pad Plated Over POFV Printed Over Filled Via Plate over, Cu ~20u PTH, Cu 25u Fill epoxy Provides excellent flatness in TIM side 9
Overplated Thermal Via Design Guidelines Plugged hole diameter 0,2mm 0,7mm Diameters of plugged holes in the same PCB within 0,2mm Annular ring for plugged hole min 100u Outer layer min line/space 100/100u due to thick OL copper 10
Viafarm Matrix Optimizing Orthogonal matrix Diamond matrix: 1,4x Thermal via density 1,4x copper cross area 11
Density Constrains Via Pitch PTH to PTH Min 0,4mm (according to nominal diameters) 12
Laser Viafarm Viafarm can be also combination of laser drilled + buried via Viafarm Laserdrill viafarm in combination with post-bonded ALU metal-back 13
Future Step: Copper Filled Viafarm Thermally very attractive approach, but still has very limited availability Challenging plating process, likely limited to thin PCBs only May be a good solution for thin PCB viafarm designs in the future 14
Metalback PCBs
Metal-back PCBs (Heatsink PCBs) PRE-BONDED 1 signal layer only Metalback is GND layer POST-BONDED PCB type can be selected freely Adhesive 16
PRE-Bonded Cu Metal-back PCBs PRE-Bonded Cu hetsink -Usually consist of 1,5-3mm Cu plate + PTFE dielectric -Only 1 circuitry layer, thick Cu back is GND -Usually gnd connections by z-controlled drilling Laser cavities in Cu-back LED PCB Precision milled cavities are typical 17
Post-Bonded Metal-back PCBs Post-Bonded Cu -PCB construction is not limited, can be multilayer or HDI -Possible adhesives - thin FR4 prepreg - thin acrylic - conductive -Metalback types -- Die-cut Aaluninum -- ENIG plated Aluminum HDI 1+2b+1 50u adhesive Alu 1,5mm 18
IMS For Led Application ( Insulated Metal Substrates ) Aluminum back + thermal dielectric Circuit on the top layer, white SM Laser cavities in Cu-back LED PCB 19
Coin Technology
Coin Technology Coin is a piece of solid Cu inserted/embedded into PCB. Coin is located only under the component to be cooled. 21
Principle of the Coin High Power transistor Transistor internal heatsink Solder PCB (RF) PCB (FR4) T Coin 22
Embedded Coin Cooling Performance Depending on application, coin provides about 2x cooling powercompared to viafarm which has the highest possible density 23
Main Cu Coin Types RF laminate High Tg FR4 coin Embedded Coin Coin is build in during PCB lamination, attached by epoxy from prepreg Press-fit Coin Coin pressed into plated opening after or during PCB manufacturing RF laminate High Tg FR4 coin Attached Coin Coin attachment by conductive adhesive after PCB manufacturing 24
Embedded Coin Types Embedded cavity coin (U-coin) Rf substrate High Tg FR4 High power transistor coin + cavity Most preferred construction from PCB manufacturing and cost point of view 25
Embedded Coin Types Rf substrate High power transistor T Coin High Tg FR4 coin High power transistor coin I coin 26
Aspocomp Coin Project Manufacturing methods of embedded coins Thermal simulations Thermal measurements Reliability tests Embedded coin design guidelines 27
Aspocomp Coin Project Thermal Simulations Power transistor Coin Heatsink PCB onside temperatures close the embedded coin can be 90 120 C 28
Aspocomp Coin Project Reliability Result Summary Thermal stress (cycling) pass Solder float pass Pull test pass (>1000N) Crossection analysing C-coin pass Crossection analysing T-coin some details to be improved 1x Reflow pass 4x reflow > 40s @270C some cracking in resin* 4x reflow > 40s @270C no delam or visual defect * Resin cracks close to large size T coins 29
PCB Cooling Options Benchmark
PCB Tools Benchmark Viafarm + Cost and availability + Robust construction + Long manufacturing history + can be combined to HDI as well + good efficiency of surface usage - Limited cooling power 31
PCB Tools Benchmark Metal-back + Availability + High cooling power / pre-bonded + Long manufacturing history - poor efficiency of surface usage - Limited cooling power in post-bonded - Cost 32
PCB Tools Benchmark Embedded Coin + High cooling power + Good efficiency of surface usage + Flexible from design point of view + Very local cooling - Cost in case of several components that require cooling - Still relatively new option in the market 33
Cooling by PCB Options There are several well proven options for through PCB cooling Thermal Viafarm Metalback PCB Cu Coin 34
PCB Heat Management End of the Slides!