Ask the Experts
October 2, 2017 - Updated
January 20, 2008 - Originally Posted

Flux Deposition

My production line is running boards with Package-On-Package components. Our biggest issue is joints that do not solder. Is this due to insufficient flux being applied when we dip the package? Is there an off line inspection process or machine that can inspect flux deposition on the package contact points before mounting and reflowing the package?

R. A.

Expert Panel Responses

It's hard to say for sure without seeing the location of the non-soldered joints and analyzing some of their characteristics but Amkor has done much work on POP and has published several papers on the subject. Check out all of their white papers. In particular, this white paper talks about the effect of die warpage and the use of a "dipping paste" to bridge the gap and overcome coplanarity issues. This dipping paste gives greater transcription vs. flux and can expand the tolerance band of the process. Additionally, Amkor has done work on SOP (Solder on Pad) where the top pads on the lower package are bumped and also help to eliminate open joints. I am truly NOT the expert on this but have spoken with Moody Dreiza once or twice and he is great. Suggest a call or mail to him for more help if needed.

Marc Peo
Heller Industries Inc.
Mr. Peo has been with Heller Industries for over 20 years and has been President for the past 8 years. Marc has authored several industry articles on Soldering, Flux collection, nitrogen use and Lead Free conversion.

It is highly unlikely that a dipping process is NOT providing adequate Flux. Depending on the nature of the joint failure it may be a lack of heat transfer, poor paste, contact surface finish or flux activity. All could be playing a part.

Allen W. Duck
ATEK llc
Allen Duck is a 20-year Electronics Industry veteran with Global experience in multiple fields of technology and management. He started A-Tek in 2006 to provide a sales and service channel for international equipment companies wishing to offer value based solutions to USA companies.

It might be flux, but much more likely you are not reaching reflow temperature due to the mass involved. Run a test with a thermocouple attached to the joint and verify your process.

Bob Black
North America Sales Manager
Essegi Automation
Mr. Black was the President and Co-Founder of Zevatech in 1977 and introduced first Pick and Place System at Nepcon West 1980. Bob is now the President, CEO and Co-Founder of Juki Automation Systems. He is also a Co-Founder of the SMEMA Council of IPC. He serves as a member of SMTA and SEMI..

The easiest system to use for flux inspection is the VPI-1000 manufactured by Easy Braid Inc. It features up to 400X magnification, on screen measurement and a user configurable defect library.

Edward Zamborsky
Regional Sales Manager
OK International Inc.
Ed Zamborsky is a Regional Sales & Technical Support Manager for Thermaltronics, located in New York. His position requires frequent customer visits throughout North America and the Caribbean and his position encompasses not only sales but the role of trainer and master applications engineer for all of Thermaltronics products. His expertise includes such specialties as hand soldering, convection and conduction reflow techniques, array rework, fluid dispensing equipment, and fume extraction. Ed has authored many articles and has presented many papers on topics such as; Low Volume SMT Assembly, Solder Fume Extraction, SMT Rework, BGA Rework, Lead-Free Hand Soldering, High Thermal Demand Hand Soldering, Lead Free Visual Inspection and Lead Free Array Rework.

The cause is most probably the lack of flux, provided all the reflow parameters are as per specifications. It is assumed that proper reflow temperatures and TAL are achieved. One company that I know of which makes non-contact film thickness measurement system is Lumetrics. The equipment from this company can also measure multiple layers.

Bjorn Dahle
inspīre solutions LLC
Bjorn Dahle is the President of inspīre solutions LLC. He has 20 years experience in the electronic manufacturing industry with various manufacturing equipment companies covering pick & place, screen printers and thermal process management.
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