Solder webbing @ Wavesolder

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Hi all: We are seeing "solder webbing" on the bottom side o... - Feb 06, 2001 by K

Now that's surprising that your board fabricator would say t... - Feb 06, 2001 by davef

#5150

Solder webbing @ Wavesolder | 6 February, 2001

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?

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davef

#5157

Solder webbing @ Wavesolder | 6 February, 2001

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.

3c IPC TM-650 Test Methods Manual

2.3.23B Cure (Permanency) Thermally Cured Solder Mask

2.3.23.1A 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

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