White spots on PCB

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Does anyone know what would cause a PCB to develop white spo... - May 11, 2001 by Gary Kemp

More information would be helpful. For instance: * Talk a... - May 11, 2001 by davef

Gary, You're not trying to clean these boards with Iso or o... - May 13, 2001 by Frank

Dave: Actually, I'm located in the South Bay (Santa Clara... - May 14, 2001 by Gary Kemp

The time over liquidous of the profile seems short. But the... - May 14, 2001 by davef

Gary Kemp

#6559

White spots on PCB | 11 May, 2001

Does anyone know what would cause a PCB to develop white spots all over the board following parts placement and reflow? I need help!!

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davef

#6562

White spots on PCB | 11 May, 2001

More information would be helpful.

For instance: * Talk about the distribution of the problem, including a single lot or from various lots and over components and component types on the board * Tell us about the board (ie, thickness, type, solder mask, pads coating, pad size, etc) * Describe the component(s) (ie, type, termination finish, etc) * Take us through your process steps that proceed the problem, including the reflow profile and its control * Help us with the solder and the flux you are using

Let�s talk about your residues. For instance: * Where are they located? [All over wave soldered portion, laminate only, solder mask only, solder only, specific components only, etc] * What color are they? [Many "white" residues are actually more gray or yellow, than white] * What do they look like? [milky coating, salty deposit, smooth varnish] * Are they a residue? Or they a change in color of the substrate?

In some geographic areas, people complain about this every year at this time when the moisture in the air flashes over from not so humid to beaucoup humid. If this is the case, yer not from the Bay area.

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Frank

#6567

White spots on PCB | 13 May, 2001

Gary, You're not trying to clean these boards with Iso or other solvents after using no-clean solder paste? That'll do it.

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Gary Kemp

#6588

White spots on PCB | 14 May, 2001

Dave:

Actually, I'm located in the South Bay (Santa Clara)! Good guess. Now, for more in-depth information:

So far, the distribution has been limited to one board out of 10 assembled, so far from one lot. The components assembled are exclusively passives (burn-in boards) prior to socket assembly. Board type, FR4, thickness is .062, solder mask type is SR1020, plating is tin.

The spotting is evident following the reflow process. They do not hold to a particular location i.e., around components, solder mask only, etc. but are randomly distributed. I would characterize their color as more gray than white, with smooth texture.

I had the CM send over the profile ran on the lot (no ID, so cant' be sure if this is legitimate). Top temperature is 222 deg C for approx. 20 seconds.

It appears they are a change in color of the substrate caused by delamination.

I hope this helps you. Thanks again.

Gary

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davef

#6590

White spots on PCB | 14 May, 2001

The time over liquidous of the profile seems short. But then again, who knows?

Based on what you told us, I'm guessing at a board fabrication problem, either measling or delamination. Probably the former, rather than the latter. [Now, we remember that you said the problem occurs at reflow, but it's reasonable to expect board fabrication defects of this nature to appear during that type of processing.]

1 Measeling is white crosses where the fiberglass bundles cross. That becomes the weakest point where fracturing occurs (or slight disbonding). Measling, by definition, occurs only at the intersection of two fiber bundles within the lamina. 2 Make sure we're not confusing measeling with air entrapment or delamination. Crazing and delamination, however, can occur in the same plane as the metal foil, and can become large running or bridging faults. 3 Delamination is not measling. Delamination is a rejectable defect, measling is not. Refer to IPC-A-600 for the definitions.

There is a paper [circa 1973] on measling in the on-line resource section of the IPC ste [http://www.ipc.org]. Back then, measling was a big deal, primarily because it was poorly understood. Now with better process control, measling occures much less.

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