High-performance PCB system moves the masses (PDF)

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High Performance PCB System
Miniaturisation – HDI – Thermal Management – Printed Polymer
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page 1
06.10.2015
Highly reliable printed circuit boards
and devices in automotive electronics
based on an example of a High Performance PCB System
1. Miniaturisation
 HDI Technology
 Reliability – IST
2. EmbR – printed embedded resistors


Performance - Tolerances
Reliability
3. Thermal Management
 Thermal vias
 Heat Sink
 Thermal Simulation
Stefan Keller
Product Manager
4. Costs

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FR4 instead of Ceramic
page 2
06.10.2015
High Performance PCB System
Market Requirements
Produkte
Customer‘s objectives:
 PCB size and respectively the size of the unit needs to be reduced to one 1/4 in
comparison to the currently running previous version
 Usage of complex and „small“ components
 High operating temperature (- 40 bis +140° C ambient temperature)
 Unchanged high long-term reliability, at least 10 years, 20.000 h (commercial vehicle
application)
 Harsh environmental requirements e.g. vibration, mechanical shocks
 Cost effective - competitive
Requirements for PCB manufacturer:




Competent team: technology, process development, quality management
Project management
Test equipment
Investment confidence
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06.10.2015
High Performance PCB System
Miniaturisation
Produkte
New PCB size: 1/4
1. Approach (temporary): LTCC – ceramic solution
> works, but target only partially achieved –
relatively expensive
2. Approach:
High Performance organic (FR4) - PCB System
50 x 140 mm
Combination of HDI- and Printed Polymer Technology
in connection with optimized thermal management
> Target achieved, production start at the beginning of 2015
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06.10.2015
High Performance PCB System
Miniaturisation using HDI Technology
Produkte
PCB size / unit size > Could be essential for the success of a product!
Long-standing recommendation of WE HDI Product Management:
 Reduction of the rooting area by using microvias + buried vias
instead of plated through hole vias

> perfectly implemented in the applicaton shown !
Buried Via
Microvia
Avoiding PTH Vias
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06.10.2015
High Performance PCB System
Miniaturisation by HDI Technologie
Layer stack-up HDI06_2+2b+2
 High packaging density by using Microvias + buried
vias, without plated through (PTH) Vias
 2nd Microvia layer
 Highest reliability caused by low PCB thickness
< 1.0 mm (= low Z-axis expansion)
 Base material Low CTE TG 170°, filled, halogen free
PTH vias are normally the weak
points of a PCB concerning
thermal cycle stability.
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page 6
06.10.2015
High Performance PCB System
Reliability - PCB
Produkte
Results of investigations:


Thermal cycle tests -40° / +155° C
(PCB + test coupons)
IST
 Results: each 1000 cycles
passed without any problems
Further tests were carried out on the complete
system.
Investigations by customer on the unit as well.
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page 7
06.10.2015
High Performance PCB System
Reliability - PCB
Interconnect Stress Test - IST
The IST offers some decisive advantages to the conventional
thermal cycle tests:



1000 Temperature - cycles in 4 days
Online measurement of the measuring circuit
IST = very meaningful test

Special test coupon
matched to the PCB design
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06.10.2015
High Performance PCB System
Reliability - IST

Preparation: 6 x Reflow 245° C
or 2 x 260° C Reflow-Simulation in IST
or in accordance to customer specification
 Electrical heating of coupons through powercircuit to 150°C within 3 minutes,
cooling to room temperature
within 2 minutes
 Online measurement of temperature and resistance
(+ 10 % max. resistance change permitted)
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06.10.2015
High Performance PCB System
Reliability - IST

Measurement results HDI build-up (without PTH vias)
TEST RESULTS
Coupon
ID
5209_10
5209_11
5209_14
5209_2
5209_5
5209_8
5209_9
Pwr Cycles
1000
1000
1000
1000
1000
1000
1000
Pwr %
0
-0.3
0.6
-0.1
-0.2
-0.5
-0.3
SenseA
Cycles
1000
1000
1000
1000
1000
1000
1000
SnsA %
0.1
-0.2
0.6
-0.1
-0.2
-0.5
-0.2
SenseB
Cycles
1000
1000
1000
1000
1000
1000
1000
SnsB %
Results
0.2
-0.1
0.5
0.1
-0.3
-0.4
-0.3
Accept
Accept
Accept
Accept
Accept
Accept
Accept
CusSpec
N/A
Mean
Std Dev
Min
Max
Range
Coef Var
Reliable produced
Microvias have a high
thermal cycle stability of
significantly more than
1000 IST cycles
(≙ 3000 conventional
thermal cycles)
N/A
N/A
TEST PROTOCOL: 334
------------------------------------PASS------------------------------------
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06.10.2015
High Performance PCB System
Reliability – Solder Process
IPC-7095C: „max. 22% of the image diameter“
The appearance of voids depends on:
 Flux, solder paste
 Temperature profil
 …..
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page 12
06.10.2015
High Performance PCB System
Reliability – Solder Process / Microvia Filling
As both variants,
filled and unfilled Microvias,
have advantages and
disadvantiges, WE does not give
an recommendation.
Everyone has to make their
own decision!
Copper Filling
Filling = extra charge!!
Filled &
capped
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page 13
06.10.2015
High Performance PCB System
Printed Resistors – Printed Polymer in general
Applications:
• Pull-up and Pull-down resistors
• Voltage dividers
• General circuit resistors
• High reliability requirements
Facts:
• Pastes with different resistance values
• Tolerance printing process R +/- 30 % (standard)
• Tolerance after laser trimming +/- 5 % for the entire product lifetime
• Resistor values from 50Ω to 1 MΩ (standard)
• Low temperature coefficient (≙ resistance change) +/- 300 ppm/K
• Standard size min. 1,75 mm × 1,25 mm
• Thickness of printed resistors approx. 20 µm
• Design Rules available
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06.10.2015
High Performance PCB System
Printed Resistors – Printed Polymer
WE: 10 years experience with
printed resistors and with
polymer pastes (carbon)
- Miniaturisation using
embedded resistors EmbR
- Reliability advantages
p
Lenth
R = ------- x -------0,02
Width
p = paste resistance value
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06.10.2015
High Performance PCB Systems
Printed Resistors – Laser Trimming
Tolerance of resistance value
without laser trimming
max. +/- 30%
With Laser Trimming
Process tolerance: down to +/- 1%
Entire product lifetime: +/- 5%
Traceability:
The laser trimming process can also
enable perfect traceability by using binary
coding on additionally designed resistors.
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06.10.2015
High Performance PCB System
Printed Resistors – Choice of Pastes
1. Step: extensive investigations were
necessary, in order to dertermine
which pasts could fulfil the
demanding requirements of the
complete system.
The stability of the resistance values
under temperature influence was a
particular challenge for many paste
systems.
Resistance change: 4 pastes @ 155° C
operated with max. power
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06.10.2015
High Performance PCB System
Printed Resistors – Tests
• Power Derating
Aim of Power–Derating tests is to 2
Paste
Rated Power at 70°C (mW/mm )
determine
the
max. electrical
load of the
WE-2D-250.1
179
resistor,
but not to irreversibly
damage
WE-2D-10k.1
100
the resistor. Currant is constant.
Result: even at 140° C the power
dissipation is far above the disired 50
mW/mm².
The performance of the printed resistors
is at least as good as comparable
soldered resistors or other embedded
technologies.
• Thermal Cycle Test (conventional)
-40° C / + 155° C, 1000 cycles, transfer time max. 20 s, dwell time 15 Min., resistance change max. 2 %
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06.10.2015
High Performance PCB System
Printed Resistors – Tests
Qualification of the System
Resistors and Voltage Dividers
Test
Test method
Procedure
Max. Deviation
Single Resistor
Temperature Coefficient of
Resistance (TCR)
DIN EN 60115-1:2012-04, 4.8
+20 / -40°C ...+20°C / +140°C
- 700 …– 300 ppm/K
High Temperature Exposure
(HTE)
MIL-STD-202 Method 108
1000 h @ TA = 150° C unpowered
+/- 3%
Moisture Resistance
MIL-STD-202 Method 106
25°/65°, 95% rH, 3 cycles in 24h,
10 days, unpowered
+/- 2%
Biased Humidity
MIL-STD-202 Method 103
1000 h, 85°C, 85% rH, 10 % of
operating power (50 mW/mm²)
+/- 3%
High Temperatur Operating
Life
(HTOL)
MIL-STD-202 Method 108
1000h HTE, then 1000 h HTOL @
TA = 140° C at rated power
+/- 20%
Resistance to Soldering Heat
IPC-TM650
5 times 260 +/- 5 ° C, 10 +/- 1 s
+/- 2 %
extract of the qualification programm
The same tests have been done by customer on the assembled units.
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06.10.2015
High Performance PCB System
Printed Resistors – Tests
Qualification of the System: Preparation HTOL
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06.10.2015
High Performance PCB System
Printed Resistors – Tests
Annual Re-Qualificatin of the System
Resistors and Voltage Dividers
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page 21
06.10.2015
High Performance PCB System
Thermal Management – in general
Thermal Simulation
Options on PCB basis:
• Heat dissipation using vias
• Heat spreading using planes
and heatsinks glued onto the PCBs
Target:
• Lowering of temperature at the component
• Avoiding critical temperatures inside of the
component and unit
• Extention of lifetime and ensure of long term
reliability of the unit
At threshold a thermal simulation in preliminary
stages is recommended
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page 22
Variant 2
Variant 3
06.10.2015
High Performance PCB System
Thermal Management – PCB System
Optimized Thermal Management
• High number of Microvias
(direcly in solder pads) and
buried vias
• Large cross section
• Low thermal resistance
Requirements on the
system:


Operating temperature
140° C,
for short time 150°C
ALU cooling element
with high surface finish
quality


Thick wire bondable
Sufficient adhesive
strength in connection
with thermal
conductive adhesive
• Thin thermal conductive
adhesive 50 µm
• EmbR very close to heat sink
(cooling element)
Solder resist
Thermal conductive adhesive
Cooling element

New logistical
challenge for the PCB
manufacturer
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page 23
06.10.2015
High Performance PCB System
Thermal Management – Adhesive strength
Verification of ahesive strength of
PCB on cooling element
Target: approx. 0.60 N/mm²
Pretreatment
 Thermal cycles (-40°C / +155°C) 1000 cycles
 Climate chamber 1000 h (85°C / 85% air humidity)
 Hich temperature exposure (HTE Test)
1000 h in oven / 155°C
Result:
Necessary to ensure required adhesion strength:
 Lamination considering defined pressure,
temperature and time parameters
 Surface tension ALU min. 38 mN/m
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06.10.2015
High Performance PCB System
Thermal Management – Simulation PCB bottom side
Ambient
temperature:
140°C
Max.
temperature
at
resistor:
153.5 °C
Power in
accordance
with
customer
specifikation
Thermal Simulation - Würth Elektronik CBT Product Management
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page 25
06.10.2015
High Performance PCB System
Thermal Management – Thermography Measurement
PCB bottom side
The thermography measurements
essentially confirm the results of the
simulation.
As these measurements are very complex,
only a limited number of resistors could be
investigated.
Ambient temperature 140° C
Resistors powered with 5-30 V (HTOL Test)
Measurement after 60 minutes
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06.10.2015
High Performance PCB System
Thermal Management – Thermography Measurement
PCB Top side
The thermography
measurements show that
critical hot spots,
caused by powered resistors,
are avoided, also on the PCB
Top side.
Ambient temperature 140° C
Resistors powered with 5-30 V (HTOL Test)
Measurement after 60 minutes
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06.10.2015
High Performance PCB System
Costs
FR4
Ceramic
•
•
High temperature
resistance
•
•
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page 28
High
funktionality
Highest
packaging
density
Cost-efficient
06.10.2015
High Performance PCB System
Costs – PCB in general
 Main advantage FR4 PCB: manufactured in „large“ production panels
PCB Cost drivers
Presented System
PCB size
+
Unfavourable delivery panel
/ X-Out
++ Single PCB
Complex build-up
≈
Material costs
++ Only one core, four pre-pregs, TG170
Mech. drilled vias
++ Only buried vias in a thin core
Number of plating steps
≈
Only three „simple“ plating processes
Complex contour machining
+
Simple milling contour
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Relatively small size
Two lamination processes
page 29
06.10.2015
High Performance PCB System
Requirements on PCB Manufacturer
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Metallurgic analysis
Inspection according to IPC-6012 Class 3
Stereo/optical microscopy (VIS/UV)
IR camera
Ionograph
CAF Measurement equipment
Climate test chamber
Thermal Cycle Test
IST
High Current Impulse Test
Pressure Cooker Test
X-Ray fluorescense spectroscopy
Thermal simulation
Testequipment for
• HTOL
• Power Derating
Labview - controlled
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
Collaboration with institus
•
•
•
•
•
REM/EDX (Uni Basel, EMPA Zürich)
FIB (Uni Basel, EMPA Zürich)
XPS (IGB Stuttgart)
Wetting tests (ISIT Itzehoe)
Ultrasonic microscopy (ISIT Itzehoe)
06.10.2015
High Performance PCB System
Summary
• Miniaturisation by
- HDI Technology
- Printed resistors (Printed Polymer)
• Highest reliability using a thin HDI build-up without PTH vias
• A technology combination of
- HDI
- Printed resistors
- Optimized Thermal Management
can enable a cost effective substitution of a ceramis solution by a
FR4 - PCB
• A competent and broadly based PCB manufacturer can realize such a task.
System solutions will be an essential part of collaboration in the future.
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page 31
06.10.2015
Produkte
Systeme
Dienstleistungen
Knowing the relationships - is a secret of success!
We are looking forward to
good cooperation!
Stefan Keller
Product Manager
[email protected]
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06.10.2015