Hi all: We are seeing "solder webbing" on the bottom side of some of our PCBs after wave solder. The solder is sticking (like a spider web) to the solder mask on the PCB.
This is only happening on 2 of the many PCBs we wave on that machine. Both of these problem children are fabricated at the same Board house. I've communicated the issue to them & they claim the mask is cured properly.
Does anyone have a test I could use to prove or disprove the solder mask is the issue or not?
I thought I found something in one of the archives on this, and a certain solvent was recommended that could be applied to a swab & rubbed over the solder mask -- if the swab had a green residue on it- it meant the mask was not cured -- well I cannot find that thread in the archives. Does anyone know of such a solvent or test?
Does anyone have any other recommendations to help us determine the root cause?
Now that's surprising that your board fabricator would say the mask was cured properly [without even inspecting the boards]. I wonder if they can backup those BOLD words when testing your boards with the webbing problem.
The reason you can�t find the thread that you recall in the "no longer fine" SMTnet Archives is because those files didn�t make it back to us during the last conversion of SMTnet to Cold Fusion. Sad story. Hopefully, Mike will fix that some day.
I too recall a thread on testing for solder mask cure. Here�s what I�ve got ...
3 Checking for mask cure. Approaches are:
3a Drop methelyne chloride, one drop at a time, wait one minute and check for degradation. Repeat drop ...
3b A little ethyl acetate on a Q-tip will tell you. Drag it across the mask and see if it comes up green. If it does, you're not fully cured. I think ethyl acetate is a little more user-friendly than MEK.
18.104.22.168A Cure (Permanency) UV Initiated Dry Film Solder Mask
We too are usually quick to jump on our board fabricator when we see webbing, but looking at a broader picture ...
Judd in "Soldering in Electronics Assembly" lists just about everything short of Mother Teresa as cause for webbing, including poor play of the XFL.
Klein-Wassink in "Soldering In Electronics" talks about * Incorrect distribution of flux * Oxidation of solder at the point where the board looses contact with the solder bath [possibly a flux problem] * Contamination of solder * Incorrect predrying of solder paste * Use of poor quality solder
Manko in "Soldering Handbook For ..." lists * Improper curing of the solder resist * Poor formulation of the resins in the solder mask * Rough board surface [during premask prep] from poor board fabrication control * Contact between molten solder and / or dross and a PCB that is starved for flux * Not uniform flux application