BGA Reliability - · PDF fileDistorted BGAs Distorted BGA reliability Some issues seen in previous with bowed BGAs Probably due to moisture ingression (pop-corning)

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BGA Reliability –The Effects of

Solder Joint Voiding and Uneven Stand-

Off Height

Martin Wickham, National Physical Laboratory, Teddington UK

National Physical Laboratory Webinar

30th April 2013

[email protected]/ei

NPL Management Ltd - Public

BGA Reliability - Summary

Electronics Interconnection and NPL

BGA reliability measurement

Pb contamination of BGA joints

BGA voids and reliability

BGA standoff and reliability

Distorted BGA joints and reliability

2


The Effects of Solder Joint Voiding and Uneven Stand-Off Height

BGA Reliability and NPL


30th April 2013



4

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BGA Reliability Measurement


30th April 2013



Reliability of Solder Joints

Degradation of solder due to fatigue of solder

Cyclic changes in ambient temperature



Thermal Cycle Testing


Electrical Testing During Cycling

Failure of joints determined by monitoring electrical resistance.

Closed and open circuit monitoring Only minor changes in joint

resistance prior to failure compared to test circuit resistance

Use of dummy daisy-chained components



B

C

D

A 16151413121110987654321

R Q P N M L K J H G F E D C B A

BGA Failures

BGA failures ring dependent

Rings adjacent to outside of silicon die fail first

TCE constrained by silicon

Commons


Constant/Continuous Monitoring

Failures in thermally cycled joints most often occur during the hot side of the cycling As component expands more than substrate, crack

“opens”

During cold part of cycle, component contracts more than substrate and “closes”

Continuous monitoring of electrical resistance measures these failures earlier than monitoring at ambient temperature alone.



Pb Contamination of BGA Joints


30th April 2013



Transition Studio Project Test Assembly

Components Paste PCB Vibration

A SnPb SAC ENIG No

B SnPb Sn62 ENIG No

BV SnPb Sn62 ENIG Yes

D LF Sn62 ENIG No

DV LF Sn62 ENIG Yes

E1/2/3/4/5 LF Mixed ENIG No

R0603

R1206

PBGADIP

MELF

CGA

SOIC QFP

R0603

R1206

R0603

R1206

ControlledLead-content

• Approx. 250,000 soldered joints

• 2000 cycles (-55 to 125oC, 5min dwell, 60min period)



BGA Thermal Cycling

Electrical test failures mainly occur in C-rings adjacent to chip within package– SnPb solder with SnPb BGAs, failures in all rings

– SAC solder with SnPb BGAs, failures in C-rings

– SnPb solder with SAC BGAs, no failures

– SAC solder with SAC BGAs, failures in C-rings

– Contaminated solder with SAC SOICs, some failures in C-rings

Components Paste A-ring B-ring C-ring D-ringA SnPb SAC 0.0 0.0 79.2 0.0B SnPb Sn62 13.0 30.4 91.7 30.4D LF Sn62 0.0 0.0 0.0 0.0E1 LF SAC 0.0 0.0 15.8 0.0E2 LF 1%Pb 0.0 0.0 5.9 0.0E3 LF 2%Pb 0.0 0.0 10.0 0.0E4 LF 5%Pb 0.0 0.0 0.0 0.0E5 LF 10%Pb 0.0 0.0 10.0 0.0

BC

D

A16151413121110987654321

R Q P N M L K J H G F E D C B A


Alloy Comparison - PBGA256 T/C Failures

SnPb BGA + Sn62 solder

SnPb BGA + SAC solder

SAC BGA + mostly SAC solder



BGA Voids and Reliability


30th April 2013



Voiding Build & Inspection

Two SAC pastes in conjunction with two profiles to give three different levels of voiding

Voiding measured using Dage X-ray system under same conditions Auto inspection routine

5120 BGA joints per condition

Thermal cycling 3000 cycles, -55 to 125°C, 5min dwells, ramps 10°C/min



Void Calculation

A1 OK Overall void 0.000 %

















BGA Images

A239

A236

G236



G236

Enhanced Image


BGA Voiding Levels

0

2

4

6

8

10

12

14

A239 A236 G236

Sample Set

% V

oid

ing

Max

Min

Average

Suggested IPC failure limit



BGA Voiding Failures

G236– 18 out of 20 devices have joints over 9% voiding

– 49 joints over 9%

A239– 2 out of 20 devices have joints over 9% voiding– 2 joints over 9%

A236– 2 out of 20 devices have joints over 9% voiding

– 2 joints over 9%

– Are BGA failures related to devices with high voiding?

– For analysis at 2000 cycles, voiding will need to occur in C-ring


BGA Electrical Failures

Failure criteria = 100% of all ringsAll failures in C ring

0%

20%

40%

60%

80%

100%

0 500 1000 1500 2000 2500 3000

BGA-C G236BGA-C A236BGA-C A239

HIGHMEDLOW

BCD

A



BGA Conclusions

At 3000 cycles Only BGA failures in C-rings

No apparent correlation between voiding levels and failures

Position of ball in relation to die is more important than voiding level

Devices which fail IPC7095 do not show appreciable reduction in reliability compared to those which pass

Position of void within joint not analysed



BGA Standoff and Reliability


30th April 2013




T/C Test Board Design

Components 6 x PBGA256

As received SnPb

As received SAC

Reterminated with SnPb x2

Sn62 solder paste

Testing Thermal cycling

-55 to 125oC

Constant monitoring

Micro-sectioning

Shear

Shear

Component as-received RETB RETC

PBGA256 SnPb/SAC SnPb SnPb

R2512 Sn SnPb SnPb

R1206 Sn SnPb SnPb

SOIC14 Sn SnPb SnPb

PQFP100 Sn SnPb SnPb


BGA Standoff

Component Interface to Interface Standoff

PBGA SnPb control 0.29mm

PBGA RET B 0.30mm

PBGA RET C 0.38mm

PBGA SAC 0.30mm



BGA Xc

-20

0

20

40

60

80

100

0 500 1000 1500 2000 2500 3000

Cycles

Me

dia

n R

an

k (

%)

RET30BRET30CRET30SnPbSAC305Linear (RET30B)Linear (RET30SnPb)Linear (RET30C)Linear (SAC305)

Increasing standoff

SnPb

SAC

•Please note that SAC and SnPb results will

be different for testing at other strain ranges

Component Standoff

0.30mm0.29mm

0.38mm


Distorted BGA Joints and Reliability


30th April 2013




Distorted BGAs

Distorted BGA reliability Some issues seen in previous with bowed BGAs

Probably due to moisture ingression (pop-corning)

What effect on BGA reliability?

31


Thermal Cycling of Distorted BGA Joints

Distorted BGA joints occur with bowed components (pop-corned)

Simulate problem by “canting” BGAs during reflow to produce distorted joints

32



Fabrication of Distorted Joints

Use of shims and spring clips during BGA placement to manipulate standoff

33


Test Assembly

Practical components, SAC alloy PBGA256, 1.0 mm pitch Used in several NPL project

so comparable reliability data available

LF profile

SAC 305 no clean paste

34



Revised interconnect design

35

Each group of same joint height and distance from centre of BGA

Normal daisy-chain Canted daisy-chain


Standoff Height

Average Left height Average Right Height

cant00X (control) 2.19 2.19

cant10X 2.05 2.32

cant20X 2.19 2.41

36

PCB thickness = 1.6mm

Cant00X



Cant00X - Control

37

Cant00X


Cant10X

38

Cant00X



Cant20X

39

Cant00X


Standoff Heights

40

0

0.1

0.2

0.3

0.4

0.5

0.6

Pad

to Pad Height (m

m)

Cant00X

Cant10X

Cant20X



Thermal Cycling

2000 thermal cycles

-55oC to 125oC, 5 min dwells, ramp ~ 10oC/min

Constant monitoring of test assemblies

No electrical test failures during testing

41


Cant00X - Control

42

Left side Right side

Cant00X



Cant00X - Control

43

Component side Component side

Solder masked defined pads on component


Cant10X

44

Cant00X

•Slight misalignment due to spring clips



Cant10X – Taller Joints

45

•Little damage on taller joints


Cant10X – Centre of Component

46

•Increased damage component side



Cant10X – Shorter Joints

47

•Joint failure on one side of short (component side)


Cant10X – Shorter Joints

48

•Near failure on other side of short (component side)



Cant10X – Shortest Joints

Limited damage (component side) on shortest joints (no short)

49


Cant20X

50

•Little damage evident

Cant00X



Cant20X

51

•Little damage evident even on shorter joints


Summary Distorted Joints

No measured electrical failures

Limited damage in majority of joints after 2000 cycles

Joint failures did occur with shorter joints in association with shorts

52



Colleagues and collaborators

NPL - Chris Hunt, Milos Dusek & Ling Zou

Collaborators

53

ACE Production Technologies in association with Gen3 Systems

Aero Engine Control Systems

Aeroflex

Alcatel

AMS Radar Systems Division

BAe Systems

Bookham

Bosch

Celestica Ltd

CML.

Dage

Dolby Laboratories, Inc. (UK)

Datapaq Limited

ESA

Eurotherm

Fujitsu Telecoms Europe

General Dynamics

Hansatech

Henkel

Invotec

MBDA (UK) Ltd

MicrossRolls Royce plc

Retronix

Rohm & Haas

Rolls Royce

Selex

Soltech

TRW Automotive

Thales Defence Electronics

BGA Reliability –The Effects of

Solder Joint Voiding and Uneven Stand-

Off Height

Martin Wickham, National Physical Laboratory, Teddington UK


30th April 2013


Documents

BGA Reliability - · PDF fileDistorted BGAs Distorted BGA reliability Some issues seen in previous with bowed BGAs Probably due to moisture ingression (pop-corning)