TOPIC: iNEMI PCB Warpage Characterization and Minimization REPORTER: Mike HuangAFFILIATION: Material Analysis Dept., WistronEmail: Mike_Huang@wistron.com

Paper Code: Date: Wed, Oct 21, 2020

1 INTRODUCTION2 Repeatability of DOE3 Summary4 QUESTION & ANSWER

2

OUTLINE

• Development trends of Electronic Product - Miniaturization- Multi-function

• Due to the use of thinner components and printed circuit boards (PCBs < 1 mm) , PCB warpage risks increase, which in turn impacts surface mount technology (SMT) yield due to soldering defects such as bridging, non-contact opens, and non-wet opens.

• Challenge - Specification: IPC Standard/IPC-TM-650 (Bow & Twist) only states warpage

level for incoming PCB, it is not sufficient to address the warpage at elevated temperature.

- Investigation: Lack of extensive studies about PCB process and layout design on PCB warpage behavior.

Introduction

Component

PCBSolder Joints

Solder joints

Normal Condition Bridge Non-contact opens Non-wet opens

Solder Ball + Solder Paste

• Project Title- PCB Warpage Characterization and Minimization

• Purpose- Understand the possible factors of PCB warpage from PCB process,

PCB Design and PCB assembly process.• iNEMI Team Members

Introduction

iNEMI : International Electronics Manufacturing Initiative

Introduction

• DOE Matrix (Original Plan)- Phase 1 (PCB fabrication)

ü 1.PCB lamination process ü 2.PCB location within manufacturing panel (center vs. corner)ü 3.PCB post processing (PCB pre-bake before shipment to customers, Yes vs. No)

ü 4.PCB thickness (0.8mm and 0.6mm)ü 5.PCB material (Mid Tg vs. High Tg)ü 6.PCB fabricators (Supplier A / B)

- Phase 2 (PCB design)ü 1.PCB copper balance across layers ü 2.PCB outrigger to board area copper balanceü 3.PCB panel dimensionü 4.PCB thickness (0.8mm and 0.6mm)

- Phase 3 (Board assembly process condition)ü 1.Reflow pallet material ü 2.Reflow pallet support conditionü 3.PCB panel dimensionü 4.PCB thickness (0.8mm and 0.6mm)

- PCB dimension: 200x140mm- Panel: 4-up multi-panel- Board dimension: 79x56mm- Layer count: 10 layer- PCB thickness: 0.8 & 0.6 mm - Key components: 0.5 & 0.4mm pitch BGA, shield- Warpage Measurement

ü BGA area: 13 * 13 mmü Panel area: 200 * 140 mm

• DOE Sample

BGA area

Panel area

Introduction

DOE Factors Level 1 Level 2PCB fabrication house Supplier A Supplier BPCB fabrication process Condition A Condition BPCB location within manufacturing panel Center CornerPCB thickness 0.6mm 0.8mmPCB material Mid Tg High TgPost processing (Baking) Yes No

DOE Leg PCB Fabrication Process PCB Material PCB Thickness (mm) Post Processing1 Condition A Mid. Tg 0.8 No2 Condition A Mid. Tg 0.8 Yes3 Condition B Mid. Tg 0.8 No5 Condition A High Tg 0.8 No7 Condition B High Tg 0.8 No9 Condition A Mid. Tg 0.6 No

11 Condition B Mid. Tg 0.6 No13 Condition A High Tg 0.6 No15 Condition B High Tg 0.6 No

Summary of DOE Legs (Phase 1 / PCB fabrication)

Summary of DOE Factorial Conditions (Phase 1 / PCB fabrication)

Introduction

APEX_2020_INEMI_PCB_Warpage

The results from following pages have been published in APEX_2020.

Introduction

BGA Coplanarity at 240 °C

w/o baking w/ baking

For the BGA area coplanarity it was found that post processing had very little effect on the BGA coplanarity

APEX_2020_INEMI_PCB_Warpage

Baking Condition: 150C for 2 hrs

Introduction

BGA coplanarity vs. the shipping panel location within the manufacturing panel is statistically equivalent

APEX_2020_INEMI_PCB_Warpage

BGA Coplanarity at 240 °C

Introduction

Shipping panel coplanarity versus DOE leg by vendor

APEX_2020_INEMI_PCB_Warpage

Panel Area Coplanarity at 240 °C

Introduction

- The key finding of this work is that PCB manufacturing and processing hasthe greatest impact on PCB warpage.- The iNEMI team would like to confirm the repeatability of the PCBmanufacturing process for both vendors A & B.- Based on the repeatability of the PCB warpage results, the processingconditions A & B will be optimized for a final round of testing in order to seeif vendor A can produce PCB warpage results similar to vendor B.

APEX_2020_INEMI_PCB_Warpage

Next Steps

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Attribute

VendorA Vendor B

Condition A Condition B Condition A Condition B

Mid Tg High Tg Mid Tg High Tg Mid Tg& High Tg Mid Tg& High Tg

Lamination Temp. (curing) °C >170 >190 >170 >190 170 175

Heating Rate (°C/min) 1.77 2.85 1.43 2.28 1.58 (inner PCB) 1.62 (outer PCB) 2.4

Cold Press Time (minutes) 40 40 70 70 40 70

Cure Time (minutes) 77 110 103 122 96 70

Leg PCB Fabrication Process PCB Thickness (mm) PCB Material Vendor Number of panels Test Site9 A 0.6 Mid Tg (S1150GB) A 12 Akrometrix

11 B 0.6 Mid Tg (S1150GB) A 12 Akrometrix

9 A 0.6 Mid Tg (S1150GB) B 12 Akrometrix

11 B 0.6 Mid Tg (S1150GB) B 12 Akrometrix

17 C 0.6 Mid Tg (S1150GB) A 12 Akrometrix

17 C 0.6 Mid Tg (S1150GB) B 12 Akrometrix

DOE Condition

Vendor A

Vendor B

Repeatability of DOE

Parameter of DOE Re-test

Repeatability of DOE

Vendor A Vendor B

Lot 1 Lot 2 Lot 1 Lot 2

Leg 9Leg 11 Leg 9Leg 11Leg 11 Leg 11

Leg 9Leg 9

BGA è Vendor A è some variability between lotsBGA è Vendor B è More variability in Lot 2 vs. Lot 1Overall è There is some lot to lot variation

BGA Coplanarity at 240 °C

Repeatability of DOE

Vendor A Vendor B

Lot 1 Lot 2 Lot 1 Lot 2

Leg 9 Leg 11

Leg 9

Leg 11

Leg 9 Leg 11

Leg 9 Leg 11

There is lot to lot variation and the fabrication process is not repeatable

Panel Area Coplanarity at 240 °C

Repeatability of DOE

Aluminum Plate

Aluminum Plate

Aluminum Plate

Cu foilPCB Board

Cu foil

Cu foilPCB Board

Cu foil

Aluminum Plate

Aluminum Plate

Cu foilPCB Board

Cu foilCu foil

PCB BoardCu foil

PCB Vendor A PCB Vendor B

PCB Process Discussion - Press/Lamination

Repeatability of DOE

PCB Vendor B

Lot1 / Voltage Machine(電壓機)

Lot2 / Oil Pressure(油壓機)

PCB Vendor A

Lot1 and Lot 2 / Voltage Machine(電壓機)

PCB Process Discussion - Press/Lamination Equipment

Summary

• Repeatability of DOE resultsü BGA area / Panel area coplanarity : lot to lot variation

• All factors that impact warpage repeatability between suppliers is not fully understoodü PCB supplier manufacturing is a key factor that impacts warpage ü Other factors that may of impacted repeatability is supplier experience with working with PCB

material, PCB material lot-to-lot variability, variability in the press-lamination machine used, etc.

Panel Area Coplanarity at 240 °C PCB Vendor A PCB Vendor B

Logo of Affiliation

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The EndThank you!

IMPACT-EMAP 2020Oct 21 (Wed) – 23 (Fri)

Taipei Nangang Exhibition Hall