Material Needs and Reliability Challenges in Automotive Packaging Under Harsh Conditions

Material Needs and Reliability Challenges in Automotive Packaging Under Harsh Conditions

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Description: Typical harsh environments for Automotive electronics include – Extreme temperatures, temperature cycling, high humidity. Underhood components – ambient temperature can be 150˚C or higher (may range 175ēC - 200ēC, and peak temperature may even higher). Extreme temperature cycles - thermal expansion coefficients of materials in the system and ICs are very important.

Other potentially damaging conditions include corrosive environments, electrostatic discharge (ESD),high voltage environments electromagnetic interference (EMI), vibrations, physical impact etc..

 
Author: Varughese Mathew  | Visits: 415 | Page Views: 577
Domain:  High Tech Category: Semiconductors 
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Contents:
MATERIAL NEEDS AND RELIABILITY
CHALLENGES IN AUTOMOTIVE PACKAGING
UNDER HARSH CONDITIONS
Varughese Mathew
NXP Semiconductors
6501 William Cannon Drive, Austin TX, USA

Automotive Innovation Driven by Electronics
Advanced Driver
Assistance Systems
(ADAS)
Security and
Connected
Network

Infotainment
Audio & Amplifier
Application
Processors

Advance Energy
systems
Advance
Batteries
Electric Motor
Drivers
2

Safe Autonomous
Systems
Smart Sensors
Radar and Vision

Powertrain & chassis
Pressure/ motion
sensors
Battery management
engine controllers,
transmission controllers,
voltage regulators
Body Controls
Suspension, traction,
power steering Position/
Angle sensors

Safety
Airbag
Collision avoidance
Vehicle stability
system

Harsh Environments in Automotive Electronics
 Harsh Environments - Cause extreme stresses and device failures.

 Typical harsh environments for Automotive electronics include – Extreme
temperatures, temperature cycling, high humidity.
 Underhood components – ambient temperature can be 150˚C or higher (may range
175ºC - 200ºC, and peak temperature may even higher).
 Extreme temperature cycles - thermal expansion coefficients of materials in the
system and ICs are very important.
 Other potentially damaging conditions include corrosive environments, electrostatic
discharge (ESD),high voltage environments electromagnetic interference (EMI),
vibrations, physical impact etc..

This presentation focuses on reliability and material concerns under extreme
temperatures and temperature cycling.

3

Varughese Mathew

Challenges in Automotive Packaging

Extended Reliability

Life time reliability for wide temperature range and extreme
conditions
Vehicle life for >>10 years

Advanced
Functionality

Zero Defect

Basic functions

Sense

Think

People trust their life on some functions
Zero defect for AEC Q100 Grade 0 for production

Cost sensitive Manufacturing – Achieve the above three cost effectively.

4

Varughese Mathew

Act

Reliability Requirements
 The Automotive Electronics Council (AEC) defines requirements for automotive grade
electronic components.
 AEC Requires Grade 0 or 1 for Harsh environments.

Power Train
Grade 1 & 0

Body
Grade 1

Chasis &
Safety
Grade 1

ADAS
Grade 1

Discrete
Grade 2 & 3

 Packaging reliability is governed by materials and interfaces.
 Wire and mold compound-metal interface reliability at high temperature / temperature cycle are
two key areas of focus.

5

Varughese Mathew

Improved high temperature reliability with Cu wirebonding
 Au wire bond (Al-Au ) cannot pass
high temperature (> 175º C)
reliability requirements due to
excessive Au-Al intermetallics and
Kirkendall voiding.

Au wire
1620hr HTB-175ºC

 Leading automotive electronic
packaging SO ,QFP, BGA and
QFN demonstrated AEC Q100
Grade 1/0 realiability .

Cu wire1620hr HTB-175ºC

 Au-Al: Au-Al intermetallics and voids continue to
grow with HTB. ~6um IMC measured at 1620hr
HTB-175ºC.
 Cu-Al: IMC thickness averaged ~1um. IMC
formation with Cu wire slow and can pass AECG0
HTB conditions.

However Cu wirebonding (CuWB) /Epoxy mold compound (EMC) has several challenges to
overcome to achieve reliability under harsh conditions.
Varughese Mathew and Tu Anh Tran – IMAPS -2012 - 45th International Symposium on Microelectronics
6

Varughese Mathew

Copper Wirebond (CuWB) Reliability
 Bonding of Cu to Al form various Cu-Al
Intermetallic compounds (IMC) such as
Cu9Al4 (close to Cu) , CuAl, CuAl2
( Close to Al).

Mold
compound

Cu ball bond
Cu9Al4 CuAl CuAl2

Al

Al

 CuWB failure is mainly caused by the
corrosive opening of IMC at the Cu-Al
interface.

Good Cu- Al bond

Failed Cu- Al bond
Atomic Ratio

 Cl- ion concentration and pH of the mold
compound matrix are two of the key
factors influencing corrosion.

+9

Locations
1, 3, 6
2
4
5
7
8

Al :Cu
Pure Cu
8.07 : 18.06
0.91 : 20.24
8.78 : 8.41
8.13 : 16.09
5.97 : 14.7

CuWB Failure Mode
Mold compound is a major source of various corrosive ions. What is impact of these
ions on CuWB reliability?
Varughese Mathew, Sheila Chopin, Leo Higgins and Ingrain Zhang, IMAPS 2013 - 46th International Symposium on Microelectronics

7

Varughese Mathew

Impact of bias voltage on CuWB corrosion reliability
 pH and corrosive ionic concentration( Cl )
of the mold compound matrix along with
applied bias determines/influences CuWB
reliability.

Fail

Pass

 As the biased voltage increases either the
pH should be higher towards the neutral
region or the Cl concentration be lower in
order to avoid a corrosive opening and
CuWB failure.
 Bromide ions can also cause corrosion in
an additive fashion with Cl.

Influence of pH , Cl concentration and bias voltage
on CuWB reliability

 Some ions in the mold compound matrix is
beneficial or benign.
If the mold compound matrix Cl concentration is kept low with a pH high, even at a
relatively high voltage ( studied up to 65V) no corrosion failure observed.
Varughese Mathew and Sheila Chopin -IMAPS 2015- 48th International Symposium on Microelectronics

8

Varughese Mathew

HTSL (High temperature storage life) Reliability
A

B
Cu
Al

C

Copper WB ball shear strengths
after HTSL for CuWB dies
encapsulated with sulfur
compound containing mold
compounds ( Sulfate – A- 35-40;
B- 40-45 ppm).

EDX- Site 4
(Si O,C, Cu)

D

EDX Site 5(Al, Si O, C, Cu)

FIB cross-section of CuWB ball bond after 2016 hours of HTSL
at 175 °C - (A) – CuWB ball bond (B) Cu-Al interface (C) EDX
spectrum of site 4 (D) EDX spectrum of site 5.

 No gaseous sulfur compound detected at high temperatures (up to 200 C)
 Bare Cu wire( 1mil- passed AECG0 -2X conditions.
Pd coated Cu wire HTSL behavior different than bare Cu wire
Varughese Mathew and Sheila Chopin -Journal of Microelectronics and Electronic Packaging (2015) 12, 226-231

9

Varughese Mathew

HTSL Reliability due to S compounds – Pd Coated Cu wire

Site-4

Cu

Site-3

Cu

Al

Al

Cu

Si

Si
Cu
Si
C

O

C O

Si

(8.8 ppm sulfate) after 1008
hrs. of HTSL stress.
The CuAl IMC – Al interface was
found to be intact and not corroded.
No significant corrosion of any part
of the ball bond. EDX at various
sites did not indicate presence of S.

o

S

(34.5ppm sulfate) after
1008 hrs. of HTSL stress.
No corrosive opening occurred at
the CuAl IMC-Al interface. Some
level of copper corrosion (voiding
of copper) close to the periphery of
the CuWB ball bond. S is detected
in the area. No open failures.

C

O

Al

S

(47.5ppm sulfate) after
1008 hrs. of HTSL stress.
Experimental sample
Extensive corrosion was
observed and corrosive
opening was also present
leading to electrical open
failure. S was also
detected.

Varughese Mathew and Sheila Chopin -Journal of Microelectronics and Electronic Packaging (2015) 12, 226-231

10
Varughese Mathew

Al pad corrosion
 Al pad can also undergo
extensive corrosion under
certain conditions such as
bias voltage, presence of
high Cl etc.

Non-corroded pad

Corroded pad

 This corrosion is characterized by unusually
thick Al oxide/hydroxide
 EDX detect presence of large amounts of Cl.
 Al surface has a mud-crack appearance.
FIB Cross-section of the corroded pad
V. Mathew et al. ;IMAPS 2016- 49th International Symposium on Microelectronics

11

Varughese Mathew

High temperature reliability with Over Pad Metallization (OPM)
 Both Au and Cu wires on
OPM(nickel / palladium /
immersion gold) can meet
AEC grade 0 requirements
and beyond.

Since no IMC and no
exposed Al pad present Cl
induced corrosion can be
eliminated/minimized

Au Wire on OPM (1um Ni)

No IMC

Cu Wire on OPM (1um Ni)
• No IMC
• No Al splash
• No Al remnant
• Minor Al deformation

Package Reliability Electrical Test Results for Au-OPM and Cu-OPM
Wire
Type

MSL3/260C +
AATC-C
(-65C to 150C)

Passed 4000
cycles
Passed 4000
Cu Wire
cycles
Au Wire

MSL3/260C +
HAST
(130C / 85% RH /
33.3 PSIA)
Passed 240 hours
Passed 240 hours

High
Temperature
Bake - 175C
Passed 2016
hours
Passed 2016
hours

High
Temperature
Bake - 150C
Passed 6048
hours
Passed 6048
hours

Varughese Mathew and Tu Anh Tran – IMAPS -2012 - 45th International Symposium on Microelectronics

12

Varughese Mathew

Second Bond Delamination Reliability
 A major difficulty in achieving AEC
Grade 0 reliability is second bond
delamination followed by temperature
cycling.
 For lead frame products, some of the
main material considerations are wire
type, epoxy mold compound (EMC),
die attach (DA) materials and lead
frame/die design features.

Delamination

Heel Crack

detected by CSAM

 Lead frames with roughened surfaces,
less Ag plating area, appropriate LF
design features , die/ LF design, will
help to overcome this challenge.

Mold Compound
Delamination

 Mold compound formulation can also
be engineered to improve LF- mold
compound adhesion.

13

Ag plating

Varughese Mathew

Summary
 Materials and assembly processes play a major role in addressing reliability
challenges under harsh conditions.
 Copper wire and mold compounds are key players in achieving AEC –
Q100 G0 conditions.
 Al- Cu-Al IMC corrosion ,Al pad corrosion , EMC- LF adhesion are critical
factors to be considered to achieve towards zero defectivity.

14

Varughese Mathew

Acknowledgments
Sheila Chopin
Darrel Frear
Tu Anh Tran
Leo Higgins

15

Thank you