Research
Fill the Void II: An Investigation into Methods of Reducing Voiding
Final Finish Specifications Review
DFX on High Density Assemblies
Challenges on ENEPIG Finished PCBs
Testing PCBs for Creep Corrosion
Screening of Lower Melting Point Pb-Free Alloys
Hand Printing using Nanocoated and other High End Stencil Materials
Board Processes and Effects on Fine Copper Barrel Cracks
MORE RESEARCH
Latest Industry News
Foxconn Says China Can No Longer Be 'The World's Factory'
Microsoft's new phone is ... $1,400? Why?
Hon Hai says Q2 results satisfactory
China Launches Beidou, Its Own Version of GPS
Do Engineers Live Longer? A Look at Occupational Factors' Effect on Longevity
The iPhone is still breaking sales records during the pandemic
How to Work from Home Successfully
Smartphone shipments in China plunge 35% in July
MORE INDUSTRY NEWS

Effect of Process Changes and Flux on Mid-Chip Solder Balling



Effect of Process Changes and Flux on Mid-Chip Solder Balling
Paper documents experimental work performed to understand the impact on mid-chip solder balling from the manufacturing process and flux chemistry.
Production Floor

DOWNLOAD

Authored By:


Katherine Wilkerson, Ian J. Wilding, Michael Carter, Daniel Buckland
Henkel Ltd
Hemel Hempstead, United Kingdom

Summary


This paper documents the experimental work performed to further understand the impact on mid-chip solder balling from both the manufacturing process and the flux chemistry.

Mid-chip solder balling is a defect typically associated with solder paste exhibiting poor hot slump and/or insufficient wetting during the reflow soldering process, resulting in paste flowing under the component or onto the solder resist. Once molten, this solder is compressed and forced to the side of the component, causing mid-chip solder balling.

To increase the understanding of what factors can impact mid-chip balling, a study was undertaken to examine the effects of process variants and flux chemistry. Stencil thickness, aperture size and aperture shape were all identified as potentially significant factors with regards to process influence. Testing also revealed that the volume of paste was not necessarily proportional to the number of mid-chip balls, but was more influenced by the position of the paste relative to the pad. Comparative testing of a range of flux chemistries indicated that this also had a substantial effect on mid-chip ball occurrence.

The data suggested that mid-chip balling could be controlled by both process and flux design. New methods of quantifying the severity of mid-chip solder balling are currently being investigated.

Conclusions


Mid-chip balling can most effectively be reduced by implementing the following process changes:

Changing aperture shape
Reducing stencil thickness
Changing to a cooler reflow profile
Reflow in nitrogen if a hotter profile is required

The flux chemistry can also have an impact on the mid-chip balling, however:

There is considerable variation between different fluxes
Halogen appears to eliminate mid-chip balling
It is possible to get zero mid-chip balls with halogen-free when the process is right
Hot slump has only a minor impact on mid-chip balling when the process is right
Further work is required to identify potential contributors to mid-chip balling

Initially Published in the IPC Proceedings

Comments

No comments have been submitted to date.

Submit A Comment


Comments are reviewed prior to posting. You must include your full name to have your comments posted. We will not post your email address.

Your Name


Your Company
Your E-mail


Your Country
Your Comments



Board Talk
Cleaning Reballed BGA Components
We Bake, But Still Have Delamination, Why?
Reflow For Rigid Flex
Solder Paste Volume for BGA Rework
Problems With Starved "J" Lead Joints
Delay Before Cleaning Partial Assemblies
Can a CTE Mismatch Cause Reliability Problems?
Solder Paste Transfer Efficiency - What/Why
MORE BOARD TALK
Ask the Experts
Soldering Components with Silver Pads
Environment Impact on Assembly, Printing and Reflow
Solder Balling Prediction Formula
Old Components and Blow Holes
Estimating Failure Rate During Rework
Coating to stop tin whisker growth?
Cleaning an assembled board with IPA
Remove and replace a 240 pin connector
MORE ASK THE EXPERTS