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
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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
12
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
18
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
23
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!