Electronics Assembly Knowledge, Vision & Wisdom
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

Authored By:
Katherine Wilkerson, Ian J. Wilding, Michael Carter, Daniel Buckland
Henkel Ltd
Hemel Hempstead, United Kingdom
,{url:'http://www.circuitinsight.com/videos/programs_final.mp4'}], clip:{autoBuffering:true, autoPlay:true, scaling:'scale' } }).ipad();
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
Submit A Comment

Comments are reviewed prior to posting. Please avoid discussion of pricing or recommendations for specific products. You must include your full name to have your comments posted. We will not post your email address.

Your Name


Company


E-mail


Country


Comments


Authentication

Please type the number displayed into the box. If you receive an error, you may need to refresh the page and resubmit the information.



Related Programs
bullet The Sir Reliability of Fine Pitch QFN Components Under Harsh Condition
bullet Screening of Lower Melting Point Pb-Free Alloys
bullet Solder Paste Past Shelf Life
bullet Ultra-Low Voiding No-Clean Lead-Free Paste for Large Pads
bullet Solder Paste Alloy Check
bullet Reliability of Doped Lead-Free Solder Joints Under Isothermal Aging
bullet Pressure-Less Silver Sintering Pastes for Low Porosity Joint and Large Die
bullet Microstructure and Reliability of Low AG/Bi Solder Alloys
bullet Extending Shelf Life for Jars of Solder Paste
bullet Effect of Reflow Profiling on Solder Paste Flux Residues
More Related Programs