inemi lead-free rework optimization project: phase 3...

© iNEMI 2013

iNEMI Lead-Free Rework Optimization

Project: Phase 3-Assembly and

Rework Evaluation

Project Co-Chairs:

Jasbir Bath (INEMI)

Craig Hamilton (Celestica)

Holly Rubin (Alcatel-Lucent)

1 © iNEMI 2013 1

Background

• Reliability tests in the previous iNEMI lead-free assembly and

rework project indicated a need to initiate a follow on iNEMI

Rework Optimization Project.

• Thermal fatigue life of certain components on the iNEMI

Payette board such as the CBGA937 was reduced after

rework.

• The overall project would evaluate and recommend best

practices, rework equipment requirements, impact of adjacent

component temperatures and procedures for best practice

lead-free rework processing.

2 © iNEMI 2013 2

Lead-Free Rework Optimization Project Phase 3

Phase 1 and 2 of the project have:

1. Determined rework repeatability on a range of rework equipment

2. Developed initial rework processes for mini-pot rework

3. Optimized BGA socket rework processes

4. Developed rework processes for uBGAs to prevent adjacent component reflow

Phase 3 project is to:

Assemble and Rework Boards with the developed rework processes and perform reliability testing to validate the rework processes developed

3 © iNEMI 2013 3

iNEMI Rework Optimization Project Participants

– Celestica, Sanmina-SCI, Plexus, Flextronics, Creation

– Cisco, Alcatel-Lucent

– Intel

– Senju, Nihon Superior

4 © iNEMI 2013 4

iNEMI Rework Optimization Project (Phase 3)

– Board redesign for DIMM daughter card: (Plexus)

– Board build for iNEMI Payette board and DIMM daughter card:

(Sanmina-SCI)

– SMT board and Wave assembly: (Creation)

– BGA socket rework: (Intel)

– uBGA rework: (Flextronics)

– DIMM and DIP rework (Celestica)

– ATC thermal cycling (Alcatel-Lucent)

– ATC thermal cycled board cross-sections (Plexus, Intel, Nihon

Superior, Alcatel-Lucent)

5 © iNEMI 2013

iNEMI Payette 2 Board (125mil [3.2mm] thick, OSP, 7 x 17 inch)

6 © iNEMI 2013

iNEMI Payette Board Assembly (Phase 3) (Creation)

125mil (3.2mm) thick OSP board, 7 x 17 inch

• SMT & Wave with Sn3Ag0.5Cu: Lead-free Assembly of 56 iNEMI Payette 2

boards

• Board # 1 to # 35: For 1st pass assembly then Rework and ATC testing

• Board # 36 to # 56: For 1st pass assembly and ATC testing

• Planned 32 boards to be assembled and then reworked to go into ATC

testing (Rework boards)

• Planned 16 boards to be assembled and then go into ATC testing (1st pass

boards)

• Other boards are for time zero cross-sectioning

7 © iNEMI 2013 7

SMT Reflow Profile (Topside)

Solder Joint peak temp.: 234 to 249°C.

Time over 217°C= 66 to 99 sec.

8 © iNEMI 2013

• Lead-free Wave Soldering: Issues in assembling DIMM and DIP

components, especially DIMM components.

– Wave pot temperature: 270°C, Topside board preheat temperature

120°C, Conveyor speed 2ft/min (0.7m/min)

– Issues in holefill due to thickness of board, copper ground connections

to TH component barrels and issue with wave fluxer on wave machine

– Wave fluxer was not spraying flux on the bottom side of the board

properly: alleviated somewhat by brushing some of the boards with

additional flux on the bottomside of the board using a flux brush

– Sample size for ATC for DIMM connector 1st pass and reworked boards

was reduced because of this due to low holefill on some boards.

iNEMI Payette Board Assembly

(Phase 3) (Creation)

9 © iNEMI 2013


• Wave holefill issue on J7 DIMM278 I/O connector (Board #1, J7)

10 © iNEMI 2013


• Wave holefill issue on J8 DIMM278 I/O connector (Board #5, J8)

Pin 1 (Square Pin)

11 © iNEMI 2013 11

– Adjacent Component Rework

12 © iNEMI 2013 12

Adjacent Component Group

iNEMI Payette board: Spacing between components is 0.5 inch (13mm)

Previous Findings

Based on previous J-STD-020 reflow parameters

– To maintain peak package temperature <250°C required increased bottom

heater temperatures

– Reworking the μBGAs with increased bottom heater temperatures caused

secondary reflow of the CBGA joints, and adversely impacted thermal fatigue life

13 © iNEMI 2013 13

Adjacent Component Group

Solutions Explored

– Heat shields

– Rework profile re-

optimization

Objectives

– Stay within J-STD-020D (260°C peak) parameters when reworking components

– Previous study work objective was to stay within 250°C peak temperature parameters when reworking components

– Ensure adjacent component joint temperatures remain below liquidus

14 © iNEMI 2013 14

New Lead-free UBGA Rework Profile

U40 Solder Joint peak temp.: 232 to 239°C. Time over 217°C= 60 to 74 sec.

U40 Component top peak temp.: 255°C. Time over 217°C= 109 seconds.

Less bottom

heat and more

top nozzle heat

used to

develop this

rework profile

15 © iNEMI 2013

TC LocationPeak Temp

(C)

Reworked uBGA Joint 232.9

Adjacent uBGA Joint 245.5

CBGA 1 Joint 223.0

CBGA 1 Bottom PCB 237.2

CBGA 2 Joint 218.7


CBGA 3 Joint 211.3


Joint and Package Temp Monitored Values

CBGA solder joints below & above liquidus temp.

CBGA-uBGA Interaction Study Previous Study

(Rework component top temp: 245°C)

TC Location

Peak Temp

(°C)

Reworked uBGA Joint 232

Adjacent uBGA Joint 215

CBGA 1 Joint 204

215 Reworked

232.9 245.4

223.0 237.2

218.7 237.3

211.3 245.1

Joint

PCB

Bottom side Heat Escape Hole

CBGA1

CBGA2

CBGA3

Reworked

Current Study (Rework component top temp: 255°C)

No CBGA solder joints above

liquidus temperature

232

215

204 203

Joint

PCB

Bottom side Heat Escape Hole

CBGA1

Reworked

192

Row A,

U41 U40

U27

16 © iNEMI 2013 16

Conclusions

• A new lead-free rework profile was developed which kept the

adjacent CBGA solder joints below liquidus (217°C) whilst keeping

the reworked uBGA component within J-STD-020D limits.

– This was done by reducing bottom heat and increasing top nozzle heat

compared with previous study

• Found that heat shields (Al and Ceramic) helped to reduce the temperature

of the adjacent CBGA but not to a large extent (2°C to 4°C) so not used in

Phase 3

• Cross-sectional and electrical analysis of adjacent uBGA and CBGA:

• Electrical testing showed no change between as-assembled 1st pass

components (uBGA and CBGA) and those components adjacent to the

reworked uBGA

• Cross-sections of the adjacent uBGA at U41 next to reworked uBGA and

CBGA components showed well formed joints with no evidence of

secondary reflow

17 © iNEMI 2013 17

– BGA Socket Rework

18 © iNEMI 2013

Lead-free BGA604 Socket Rework

• Create a lead-free board rework profile for the BGA 604

socket on the iNEMI Payette 2 board

• Cross-section BGA604 sockets to verify that they have good

solder joints

19 © iNEMI 2013

iNEMI Payette BGA604 Socket Profile Board Setup

TC1-4 Socket Outer Corner

Solder Joints

TC5-6 Socket Center

Solder Joints

TC7-10 Socket Top Body

TC11-12 Socket Body Top

Pin Holes

TC13 CAF1 Board Location

Note: TC1-6 are drilled from the bottom of the board & only the top of the TC is at the pad surface

20 © iNEMI 2013

BGA 604 Socket Rework Temperature Profile

21 © iNEMI 2013

•Flux activation time is above our 100sec max target on all thermocouples except TC2 (highlighted in red)

• The maximum time exceeded was only 19sec & is due to the bottom heating system in the rework machine

•The two center thermocouple locations (TC5 & TC6) had slower cooling ramp rates than what we would normally target

•Delta temperature between all TC’s was 9.5°C (within our 15°C specification for sockets)

Thermocouple

Location

Maximum Socket Body

Temperature (≤260°C)

Top Of Board Temperature At

CAF1 Location (≤217°C)

TC7 Socket Body 248.0°C N/A





TC12 Board

(CAF1)

N/A 216.3°C

Thermocouple Solder Joint

Location

Rising Ramp

Rate (0.5-

2.5°C/sec)

Flux Activation

Time (150°C to

217°C) ≤100sec

Critical Ramp

Rate (205°C to

215°C) 0.35-

0.75°C/sec

Socket Peak

Temperature

(230°C to

250°C)

Socket Time

Above Liquidus

(40-200sec)

Cooling

Ramp Rate

(0.5-

2.0°C/sec)

TC1 (Pin 1) Outer Corner 0.71°C/sec 102sec 0.60°C/sec 239.4°C 114sec -0.62°C/sec

TC2 Outer Corner 0.79°C/sec 98sec 0.58°C/sec 237.8°C 101sec -0.72°C/sec



TC5 Center 0.62°C/sec 115sec 0.56°C/sec 240.8°C 156sec -0.41°C/sec

TC6 Center 0.64°C/sec 115sec 0.53°C/sec 231.3°C 121sec -0.28°C/sec

Maximum socket body temperature was exceeded on TC9 by 0.1°C

– This TC measurement was much higher than all the other TC measurements (broken TC)

The CAF1 board TC location is below 217°C but closer to the

socket it is probably above 217°C

BGA 604 Socket Rework Temperature Profile

22 © iNEMI 2013

BGA 604 Socket Board 25 & 26 Cross-sections

• Boards 25 & 26 show the lowest & highest stand–off solder joints

– Board 25 AD1 location shows a slightly compressed solder joint but this does not affect reliability

– No issues found on new cross-sections with shorter TAL profile

Board 25 AD1 Board 25 A1

Board 26 AD1 Board 26 A1

23 © iNEMI 2013

• Board 22 cross-section shows that the socket warps down on A31 & AE2 corners

–A31 corner stand-off is approximately 2.5 mils lower

–AE2 corner stand-off is approximately 3.5 mils lower

• Boards 24, 25 & 26 cross-sections show only the AD1 corner to have a larger

collapse than all other measurements

–AD1 corner stand-off is approximately 3 to 5mils lower

• This is fairly common in socket rework from previous internal data that was obtained

Board # Cross-section Locations Stand-off Height Measurement Locations (mils)

22 A1-A31 & AE2-AE30 A1

16.68 A16

16.32 A31

14.34 AE2

12.15 AE16 15.59

AE30 15.73

24 A1-AD1 & A31-AD31 A1

17.12 M1

14.93 AD1 12.95

A31 15.73

M31 15.59

AD31 16.39

25 A1-AD1 & A31-AD31 A1

17.85 M1

14.20 AD1 12.66

A31 14.93

M31 14.85

AD31 16.68

26 A1-AD1 & A31-AD31 A1

15.73 M1

13.98 AD1 12.59

A31 14.71

M31 15.37

AD31 15.44

BGA 604 Socket Stand-off Results

24 © iNEMI 2013

BGA Socket Rework Summary

– The rework profile developed successfully

– The BGA socket stand-off measurements had up to a

5 mil delta across one side

• This is within the normal internal data range examined

– This was similar to the range observed on a different suppliers

BGA socket in previous studies

– IMC thickness measurements and elemental analysis

results were as expected

25 © iNEMI 2013 25

– Mini-pot Rework

26 © iNEMI 2013

Cross-section View of Solder Joint (274°C)

Dissolved

copper

Pad / trace

Total time in mini-pot = 60sec

Enough time to dissolve nickel layer on 135mil

thick NiAu board

Mini-pot Rework Sub-Group

Problem Statement

• Challenge

– Simulate current

production process

– Remove and replace a

PDIP without board preheat

• Rework Observations

– Achieving sufficient holefill

resulted in the copper

pad/trace dissolution on the

bottom-side

27 © iNEMI 2013

Mini-pot Rework Status (Phase 1)

• Results on iNEMI Wave Test Board indicated that an alternative alloy from SnAgCu would be needed, in order to achieve up to a 2X PTH rework, without causing quality concerns

• Mixed Sn-Ag-Cu / Sn-Cu-Ni reworks included in Phase 2 and 3 builds

Sn-Ag-Cu Sn-Cu-Ni

1X Rework

2X Rework

Phase 1

• Variation in Cu plating thickness on incoming boards were observed

– First article inspection critical before Phase 2 and Phase 3 builds

– Needed to further understand specifications and process controls

used to monitor and control copper plating thickness for as-received

boards

Low Thermal Mass PCB (62mils)

Sn-Ag-Cu Sn-Cu-Ni

1X Rework

2X Rework X

High Thermal Mass PCB (145mils)

28 © iNEMI 2013

PTH Rework Locations (Phase 2): iNEMI

Payette board, 125mil thick OSP

2 DIMM278 Connectors

3 PDIP16 Components

Note: 1st pass wave using

Sn3Ag0.5Cu

1X rework

Sn-Cu-Ni

DIP16

2X rework

Sn-Cu-Ni

DIP16

1X rework

SAC305 DIP16

1X rework

Sn-Cu-Ni

DIMM278

29 © iNEMI 2013

Mini-pot Rework Status (Phase 1 & 2)

• Further optimization of DIMM and PDIP rework process steps completed.

– Use of laminar flow well (center baffle rework nozzle) suggested and used

to reduce Cu dissolution

– Convection(batch oven) vs. Infrared (In-line) preheat studied: In-line

preheat helped preheat the board faster with less heat loss prior to rework

– Responses measured: dwell time, Cu dissolution, barrel fill & other defects

• Number of difficulties during DIMM connector rework (using Sn-Cu-Ni

alloy) which required further attention.

– Establishing adequate barrel fill (50% for ground connections), while

controlling level of Cu dissolution

Phase 2

30 © iNEMI 2013

Phase 3 PTH Rework Matrix (ATC testing)

PTH Rework Objectives:

• Validate process and

reliability of reworking a

Sn3Ag0.5Cu joint with Sn-Cu-

Ni alloy (mixed case)

• Validate process and

reliability (ATC) of reworking

Sn3Ag0.5Cu joint with

Sn3Ag0.5Cu alloy

• Measure levels of Cu

dissolution for both types of

reworked joints

• 1X rework on DIMM278

• 1X and 2X rework on DIP16

31 © iNEMI 2013 31

– Phase 3 PDIP16 Rework

32 © iNEMI 2013

Lead-free PDIP Rework

33 © iNEMI 2013


34 © iNEMI 2013


Note 1: Copper barrel thicknesses after PDIP rework were > 0.5mils (12um) on test scrap

boards during typical contact times used for SnCuNi rework

Note 2: 0.5mils (12um) was used as the minimum copper barrel thickness based on

reliability assessments published by different companies.

35 © iNEMI 2013


DIP Removal &

Replacement Average

Contact Times:

SnCuNi (1x): 30 sec

SnAgCu (1x): 40 sec

SnCuNi (2x): 50 sec

Note: Due to the narrow process window, some contact times were up to

79 seconds for 1X rework and up to 86 seconds for 2X rework which

would cause board barrel copper dissolution

37 © iNEMI 2013

•Experiments were conducted to understand the

affect of board preheat on mini-pot rework using

three different board preheat processes.

37

Effect of Board Preheat on Mini-pot Rework

38 © iNEMI 2013

Preheat Bake Process 2

1. Bake the board in the oven at 105C for 20 min.

2. Take the board from oven to solder fountain.



2. Take the board from oven to BGA Rework Machine in order to heat the board up to ~160C at

bottom side of board laminate.

3. Take the board from BGA Rework Machine to solder fountain.



2. Take the board from oven to solder fountain.

DIMM Rework (3 Board Preheat Process Evaluated)

40 © iNEMI 2013

Open

do

or

Open

do

or

Open

do

or

Open

do

or

Open

do

or

TCs 1200 1500 1800 2100 2400 Peak

(B) J7_left joint 135 135 134 133 132 255

(B) J7_center joint 137 138 137 136 135 269

(B) J7_right joint 139 139 139 138 136 251

(T) J7_left joint 135 135 134 132 132 232

(T) J7_right joint 139 139 138 137 136 230

(B) J8_center joint 136 137 136 135 134 257

(B) Laminate 2 136 136 135 134 133 167

(B) Laminate 1 135 135 135 134 133 267

(T) Laminate 1 140 140 139 138 137 141

Time at (seconds)

Reflow Profile for Process 2 (Batch Oven Bake, 150°C)

41 © iNEMI 2013

TCs 840 970 Peak

(B) J7_left joint 91 141 257

(B) J7_center joint 91 133 271

(B) J7_right joint 92 147 258

(T) J7_left joint 90 138 226

(T) J7_right joint 92 144 234

(B) J8_center joint 90 131 257

(B) Laminate 2 88 138 176

(B) Laminate 1 88 145 269

(T) Laminate 1 96 156 156

Time at (s)

Reflow Profile for Process 3 (Batch oven bake 100°C followed by

BGA rework heating of bottomside of board to 160°C)

43 © iNEMI 2013

Process Flow (DIMM 278 component)

Bake the board in oven (Ts = 105°C) ~ 10-15 min.

Move to BGA Rework Machine, Heat the board

up to 160°C at the bottom

Move to Minipot set at 265°C

Remove and replace component

Apply flux

45 © iNEMI 2013

Lead-free DIMM 1X Rework SnCuNi (J7 Location)

Evidence of low or zero copper barrel thickness

(<0.5mils, 12um) at multiple pin locations after rework

Bare Board: 1.63mils (38um)

First Pass Board: 1.3mils (30um)

46 © iNEMI 2013

Lead-free DIMM Rework (Contact times)

Average contact time for DIMM

Removal and Replacement

(SnCuNi):

27 seconds

Note: Due to the narrow process window, some contact times were up to 46

seconds which would cause increased board barrel copper dissolution after

rework

47 © iNEMI 2013

Assembly and Rework Phase 3 Conclusions

• For the 1st pass assembly build no real issues apart from

lead-free wave holefill issues on some of the DIMM 278

connectors on the 125 mil thick OSP board.

• For rework, no real issues during the BGA socket and uBGA

rework.

• More issues during mini-pot wave rework for the DIP and

DIMM component particularly for DIMM rework.

– Copper dissolution and lead-free wave rework holefill were areas

of concern.

48 © iNEMI 2013 48

www.inemi.org Email contacts:

David Godlewski

[email protected]

Grace O'Mallley

[email protected]

inemi lead-free rework optimization project: phase 3...

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