Pad Crater Project “Definition Stage”

Joe Smetana

Alcatel-Lucent

For Member Meeting 2/9/2011

San Jose, CA

The issue(s)

• Pad Cratering defects are a significant challenge with Pb-free PCB materials and/or Pb-free solders, particularly associated with large BGA devices

• Pad Pull or Ball shear testing has not shown to consistently represent the actual propensity for pad cratering of a material and in some cases can give misleading and/or opposite results from what actually occurs in real assemblies

• A way is needed to rank order materials that is directly related to actual pad cratering

Project Overview

• Create a relatively simple test vehicle with a single large BGA assembled in the middle – 6 or 8 layers, thickness .093

• Fabricate the bare boards from multiple different materials – Include a significant variety of materials, filled and unfilled

– Include materials that have also done “well” in HDPUG Pb-free materials projects

– Don’t test materials that have done poorly in HDPUG Pb-free materials projects

– Other materials as suggested by members

• Perform bend to break testing to rank order the materials – Design TV to virtually ensure trace breaks simultaneous with laminate.

– Spherical bend testing preferred or 4-point bend?

– Other

– Will need to include some amount of strain gage measurements

– Both Single Bend to Break and Repeated Load to Break

• On the same boards ALSO perform HPP testing for a correlation to actual pad cratering. – How valuable is it?

No support for this so far

What this Project will Provide

• Rank order of materials to Pad Cratering in mechanical bend testing

– At selected strain rate • 3000-3500 uε/sec (sweet spot)

– At single bend to break

– At repeated load to break • 60-70%? (TBD) lowest single bend to break load

• Correlation or lack thereof of HPP testing to mechanical bend to break testing

– Currently no support for this

Bend to Break Testing

• Meadville to support Bend to Break

testing

– Need to better define this

– 3000-3500 uε/sec is the sweet spot to

minimize scatter in the results ...

• 1000 and lower introduces a different

failure mode, 6000-7000 exhibits twice the

scatter in the results ... this is typical of

behavior seen in a brittle material.

Simplified Bend to Break Test

This will not

necessarily catch

the first break

point, but should

correlate to it and

should properly

rank order the

materials.

Key Issues

• Define the test component – Practical Components A-PBGA680-1.0mm-35mm-DC-LF-305

• PBGA 680 35x35mm Perimeter+ BGA, 1mm pitch

• 689 x 689 mil die size

• Quote of 1000 for $10,700.00

• Define the materials to be tested – Compare filled vs. unfilled, FR4 – brominated and HF,

Selected High speed materials

– Look at “cap” technologies – such as Zeta

– Select “good” materials (HDPUG Pb-free Materials 1 and 2) • Material suppliers need to supply the materials at no cost

– First Draft/Proposed Material List follows

• Define/Design the Test Board (ALU/Meadville)

• Define the required sample size – 10? Single Bend to Break

– 20? Repeated Bend to Break

Proposed Component

Rough Proposed Stackup

6 layer board - rough stackup

Prepreg - 106 or 2113 (Hi vs. Low Resin)- Cap for those specific constructions

Prepreg - 106 or 2113 (Hi vs. Low Resin)- Cap for those specific constructions

.093" over laminate

Prepreg L4 1 ounce Cu Plane

Laminate L5 1/2 ounce Cu

L6 1/2 ounce Cu

L1 1/2 ounce Cu

L2 1/2 ounce Cu

Laminate L3 1 ounce Cu Plane

Design Rough

Header

for

event

detector

attach

BGA at 45 degrees to allow for either spherical or 4 point bend

Need the following

specifics defined:

• Minimum distance

from component to

board edges?

•What type of

header or board

connector is needed

the event detector?

BGA pattern duplicated on bottom side using either VIP or SMD

pads for comparison

Considerations for Pad Cratering Test

• Materials – Filled vs Unfilled Hi Tg Phenolic Resin

– Halogen Free

– Dicy

– Mid Tg

– High Speed

– Cap Layers

• Resin Content/Glass style effect on outer layers – 106 vs. 2116 between L1-2 and N-N-1

• Pad Size – Normal vs. enlarged solder mask defined pads,

– Enlarged pads at corners

– Microvia in Pad vs. No Microvia in pad (including Dogbone Microvia vs Dogbone Through Via),

– Conformal Microvia vs Filled Micro via Note - With a single design can only do 1 of the options

Preliminary Material List (part 1)

• High Tg Filled Phenolic FR4s – Isola 370HR

– EMC EM-827

– Panasonic R1755V

– Shenzen Pacific (PIC) FL-170

– ITEQ IT-180i

– Panasonic R2125

– Grace GA-170LE

• High Tg Non-filled Phenolic FR4s – Isola 370 Turbo

– Shengyi S1170

– TUC TU-722

• High Tg Halogen Free FR4s – Grace GA-HF-17

– ITEQ IT-170GRA

– EMC EM-370(D) or EMC-370 (one but not both)

– Panasonic R1577 (Megtron 2)

– Shengyi S1165

– Ventec VT-447

– TUC TU-862HF

– Hitachi MCL-HE-679G

Preliminary Material List (part 2)

• Mid-Tg FR4s – ITEQ IT-158

– EMC EM-825

– Isola 254 - This a dicy FR4 -OK in low layer count Pb-free

• High Speed Materials – Isola FR-408HR

– Panasonic Megtron 4

– TUC TU-872L or SLK

– EMC EM-828

– MGC FL-700

– Panasonic Megtron 6

– Nelco Mercurywave 9350

• Cap Materials (over what material?) – Zeta

– Shengyi S1160F

– Hitachi KS-6600

– Hitachi CUTE

What this Project WILL NOT DO

(as currently planned)

• It will not provide data that necessarily

correlates to pad cratering occurring by

thermo-mechanical stresses – such in

reflow/cooldown as material properties

above Tg will be very different from

those at room temperature.

• If someone has an idea of how to test

this… speak up! It is a critical issue.

Where are we on this Project?

• We have held a few preliminary

meetings and some off-line

discussions with key players

– Everything is currently “draft” and

subject to change

– Delayed “active pursuit” of this project

while we finished the Pb-free materials

project

– Ready for regular meetings to resolve

open issues and move forward

Project Milestones

• Define the full extent of the Project - Team

• Define the test vehicle - Team – Component

– Board (layers, thickness, size, etc.)

• Design the Test Vehicle - ALU

• Determine materials to test - Team

• Determine the required sample sizes - Team

• Material suppliers provide materials at no cost in return for rank ordering (coded)

• Fabricators to build the test vehicle - TBD

• Procure components – Sun +?

• Assemble Test vehicles – Celestica/Flextronics?

• Bend to break testing- Meadville

• Hot Pin Pull testing (assuming we include this)

• Data analysis and reporting