What Causes Non-wetting of OSP Test Pads?

Board Talk is presented by Phil Zarrow and Jim Hall of ITM Consulting. Process Troubleshooting, Failure Analysis, Process Audits, Process Set-up CEM Selection/Qualification, SMT Training/Seminars, Legal Disputes

Phil Zarrow With over 50 years experience in PCB assembly, Phil is one of the leading experts in SMT process failure analysis. He has vast experience in SMT equipment, materials and processes. Jim Hall A Lean Six-Sigma Master Blackbelt, Jim has a wealth of knowledge in soldering, thermal technology, equipment and process basics. He is a pioneer in the science of reflow.

Transcript

Phil
Welcome to Board Talk. This is Jim Hall and Phil Zarrow, the Assembly Brothers, who by day go as ITM Consulting. Jim, today's question is from P.M.

Jim
The question is about non-wetting test pads. "What are all the probable causes of non-wetting for OSP board test pads when the circuit boards are run through our wave solder bath?"

Do you want all the reasons? We'll give you a few.

Jim
Since we're talking about wave soldering the obvious one is are you fluxing them?

If you're using a spray fluxer, are you programming exactly where the flux is being applied, are you remembering to program the spray fluxer to put flux on test pads?

The non-wetting, or poor wetting, with OSP has always been a touchy subject and a very subjective one.

An obvious problem with wave soldering is previous wave cycles. Have these assemblies seen one or two previous reflow cycles, which could have degraded the OSP coating, causing them to have poor solderability when you get to the wave, typically being the final soldering operation?

We just received our copy of IPC Specification 1601 on handling of printed circuit boards. We've touted it before because it addresses the issues of moisture absorption and baking.

Within the recommendations they do not bake OSP boards. So, a question for P.M. would be, had you baked these boards before assembly?

Obviously, we would like more data; are the through-holes soldering and not the test pads? Because if it's baking or previous heat cycles, then you shouldn't be filling your through-holes, either.

Phil
Handling being a touchy subject, you always want to exercise care. As with any kind of surface finish, keep the human contamination out. So, there are some of the reasons, if not all of them, and hope that helps.

And aside from that, it's Phil and Jim, the Assembly Brothers, saying whatever you do ...

Jim
Don't solder like my brother.

Phil
And don't solder like my brother, whether it's wave or reflow.

Comments