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

4

Cooling through the PCB Spreading and dissipating

Cooling Through PCB

5

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

Thermal Conductivity of Some PCB Materials

6

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

Most Common Tools for Cooling

Through the PCB

7

Thermal Viafarm

Filled and Capped Via

Since 2002

Metalback PCB

Since 2004

Cu Coin

Since 2012

Viafarm

9

Viafarm, Overplated Thermal Vias

Typical viafarm case

PTH, Cu 25u

Fill epoxy

Plate over,

Cu ~20u

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

Typical construction

Provides excellent

flatness in TIM side

Overplated Thermal Via

Design Guidelines

10

•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

Viafarm Matrix Optimizing

11

Diamond matrix:

1,4x Thermal via density

1,4x copper cross area

Orthogonal matrix

Density Constrains

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Min 0,4mm PTH to PTH (according to nominal diameters)

Via Pitch

Laser Viafarm

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Viafarm can be also combination of laser drilled + buried via Viafarm

Laserdrill viafarm in combination with post-bonded ALU metal-back

Future Step: Copper Filled Viafarm

14

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

Metalback PCBs

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Metal-back PCBs (Heatsink PCBs)

PRE-BONDED

1 signal layer only

Metalback is GND layer

POST-BONDED

PCB type can be

selected freely

Adhesive

17

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

Precision

milled cavities

are typical

Laser cavities in Cu-back LED PCB

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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

Alu 1,5mm

50u adhesive

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IMS For Led Application ( Insulated Metal Substrates )

Laser cavities in Cu-back LED PCB

Aluminum back + thermal dielectric

Circuit on the top layer, white SM

Coin Technology

Coin Technology

21

Coin is a piece of solid Cu

inserted/embedded into PCB.

Coin is located only under the

component to be cooled.

Principle of the Coin

22

High Power transistor

Transistor

internal heatsink

Solder

T Coin PCB (FR4)

PCB (RF)

Embedded Coin Cooling Performance

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Depending on application, coin provides about 2x cooling powercompared

to viafarm which has the highest possible density

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Main Cu Coin Types

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

coin

RF laminate

High Tg FR4

Attached Coin

Coin attachment by conductive

adhesive after PCB manufacturing

coin

RF laminate

High Tg FR4

Embedded Coin Types

25

Embedded cavity coin (U-coin)

coin + cavity

Rf substrate

High Tg FR4

High power

transistor

Most preferred construction from PCB

manufacturing and cost point of view

Embedded Coin Types

26

T Coin

coin

Rf substrate

High Tg FR4

High power

transistor

I coin

High power transistor

coin

Aspocomp Coin Project

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Manufacturing methods of

embedded coins

Thermal simulations

Thermal measurements

Reliability tests

Embedded coin design

guidelines

28

Aspocomp Coin Project

Thermal Simulations

PCB onside temperatures close the embedded coin can be 90 – 120 °C

Power transistor

Coin

Heatsink

29

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

PCB Cooling Options Benchmark

PCB Tools Benchmark

Viafarm

31

+ Cost and availability

+ Robust construction

+ Long manufacturing history

+ can be combined to HDI as well

+ good efficiency of surface usage

- Limited cooling power

PCB Tools Benchmark

Metal-back

32

+ Availability

+ High cooling power / pre-bonded

+ Long manufacturing history

- poor efficiency of surface usage

- Limited cooling power in post-bonded

- Cost

PCB Tools Benchmark

Embedded Coin

33

+ 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

Cooling by PCB Options

34

Thermal Viafarm

Metalback PCB Cu Coin

There are several well proven

options for through PCB cooling

PCB Heat Management End of the Slides!