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Old 24th May 2017, 8:51 am   #1
Goldie99
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Default Solder defect - what is it / causes it ?

Just curious as to what causes the solder defect in the attached photo (a Linn Valhalla PS board) ?

I'm referring to the 'rippling' effect which seems to be present on most of the tracks - I've seen it on other Valhalla boards, but never been sure what causes it - but I'm sure someone here does...

Alan
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Old 24th May 2017, 9:05 am   #2
MrBungle
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Default Re: Solder defect - what is it / causes it ?

It's the solder mask rippling. This is completely normal and harmless. You will find this present in a lot of things to be honest. It's annoying however. I don't think the solder masks they use these days do that.
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Old 24th May 2017, 9:09 am   #3
julie_m
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Default Re: Solder defect - what is it / causes it ?

That looks as though it was non-selectively tinned, i.e. tinned before the solder mask was applied. When the board is wave-soldered, the tinning can distort behind the mask.

When I worked in the industry, we always specified selective tinning -- only the exposed copper was tinned.
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Old 24th May 2017, 9:17 am   #4
MrBungle
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Default Re: Solder defect - what is it / causes it ?

Much prefer when it is tinned before mask. It's amazing how quickly copper disappears if you don't tin it and damage the mask during a repair. My short spell in a defence contractor repairing things suggested it was probably better to tin the whole board and not bother with the mask. Easier inspection!
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Old 24th May 2017, 9:32 am   #5
Goldie99
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Default Re: Solder defect - what is it / causes it ?

So it's essentially solder 'flowing' unevenly along the tinned tracks, under the mask ? or is it more a thermal effect / distortion of the tinning itself ?
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Old 24th May 2017, 9:50 am   #6
Craig Sawyers
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Default Re: Solder defect - what is it / causes it ?

Quote:
Originally Posted by MrBungle View Post
Much prefer when it is tinned before mask. It's amazing how quickly copper disappears if you don't tin it and damage the mask during a repair. My short spell in a defence contractor repairing things suggested it was probably better to tin the whole board and not bother with the mask. Easier inspection!
In space qualified boards, solder mask and silk screen is not allowed (outgassing, radiation damage, adhesion break down leading to flakes floating around etc etc). That makes assembly of a dense surface mount board an interesting challenge.

It is made a little less difficult by the fact that top and bottom layers cannot have tracks - they have to be buried in inner layers. So the top and bottom have only component pads and vias on them.
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Old 24th May 2017, 10:42 am   #7
MrBungle
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Default Re: Solder defect - what is it / causes it ?

Indeed. I've done some SMD prototyping and it's difficult with knife cut boards and no mask as the solder just floods all over the place.

All the boards for repair I had failed were due to cracked vias. That would scare me in high reliability applications. Might have just been the crappy in house production line though. Oh and some idiot soldering packages the wrong way round. I hated reworking big DIP packages.
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Old 26th May 2017, 9:53 pm   #8
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Default Re: Solder defect - what is it / causes it ?

Hi!

Quote:
In space qualified boards, solder mask and silk screen is not allowed (outgassing, radiation damage, adhesion break down leading to flakes floating around etc etc). That makes assembly of a dense surface mount board an interesting challenge.
What about Automotive ECUs? I've looked at quite a number of boards from these over the years and I've never come across a silk-screened or solder-masked one - is that specified deliberately to deter reverse-engineering, etc?

Chris Williams
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