Carl- This sounds like the type of board we would typically run all no clean. The secondary through hole parts would run over our selective solder as a no clean. I would worry about flux
residue if they have no way to qualify their cleaner. If the cleaner is a saponified wash, there will be less to worry about (depending on their chemistry).
If they are using DI water, the no clean flux residue from smt may turn white. At the least, I would have them verify their process with a first article even if they have to outsource a cleaning
Qualification.
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Carl Van Wormer
Sent: Friday, June 2, 2017 9:27 AM
To: [log in to unmask]
Subject: [TN] re-flow oven and wave with 2 kinds of flux? - Bayesian Filter detected spam
We have a power-control board designed for Pb-Free processing that has many surface-mount components, with parts mounted only on the top side. Several ICs and transistors are leadless (very low-profile) parts, some with thermal solder pads on the package bottom. I am requesting their no-clean solder-paste processing because of my fear of their inability to adequately clean a water-clean flux from under these low-profile parts. I fear a chemistry experiment, since these boards will be placed in an outdoor environment with uncontrolled temperature and humidity.
Question #1: Are my fears about properly cleaning water-clean flux from under low-profile parts justified?
This board has about 20 through-hole capacitors and 5 connectors (100 pins, total). Our normal assembly house has a water-clean flux Pb-Free wave-solder machine that could be used as a second pass process to add the through-hole parts at a lower cost, possibly reducing the hand-add labor charges. The wave-solder process would be followed by a cleaning in their new board-wash system. They do not currently have a method to determine board cleanliness after the cleaning process. I fear that the nasty flux may flow through holes in the board, finding ways under the low-profile SMD parts on the top of the board, creating another chemistry experiment.
Question #2: Are my fears about water-clean flux from the wave process flowing to the top side of the board, hiding under the low-profile parts, and performing long-term chemistry experiments valid?
Question #3: Should I trust a board-washing process that doesn’t have a way to verify the quality of the cleaning?
Question #4: Are there suggestions to alternative processing methods that I should consider?
Thanks,
Carl
Carl B. Van Wormer, P.E., AE7GD
Senior Hardware Engineer
Cipher Engineering LLC
21195 NW Evergreen Pkwy Ste 209
Hillsboro, OR 97124-7167
503-617-7447x303
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