Re: [PEDA] Solder mask thickness (off topic)

[Waldemar Kulajew]

> 
> OK. This is off topic (not about Protel)
> 
< -- snip -- >
> I was able to put a multimeter probe on a via and the other probe on the
> trace from that via, and after scraping the probe across the trace twice I
> went through the solder mask and got a short.
> 
> Does this sound like an acceptable Solder mask?
> 
> Thanks for any input.

Cam 

Yes, it sounds like an acceptable Solder mask to me. For fluid solder mask is
very thin over traces. If you aware the process of bringig it on the board it is
only logical. 
I tried to show a cross section below so you can see the thickness of the solder
mask over a copper trace (my fab told me about 7-8µm !)


  ___¸,ø¤º°`°º¤ø,¸___<---Solder mask
  |""|<---copper-trace 
  |  |___
  ///<---Core

That is why you easily can scratch the solder mask with a probe.



Sorry for no better news.

Regards

Waldemar


PS: I borrowed parts of the sketch from Scott May and appologice if I violate a
copyright   8-)

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Re: [PEDA] Solder mask thickness (off topic)

[HxEngr]

Re: [PEDA] Solder mask thickness (off topic)

[Dwight]

Steve,
You've had shorts under SMTs when the vias were "tented" with LPI?  I'm
concerned because we've got a board in prototype that has quite a few
under-SMT vias (32/16 size).  So far we've had no problems, but we've only
made about a dozen.  Looking at our bare boards, I see what you mean about
the soldermask drawing back from the hole on some vias, although others are
actually sealed.  But it seems there's enough soldermask to make it unlikely
for a solder bridge to be created.

Do you know what clearance you had between the vias and what size vias?
Were the shorts via-to-via, or via-to-pad?

> -Original Message-
> From: [EMAIL PROTECTED]
> Sent: Monday, March 18, 2002 8:53 AM
>
> In a message dated 3/18/2002 11:41:41 AM Eastern Standard Time,
> [EMAIL PROTECTED] writes:
> >
> > I am trying to determine if the Solder mask thickness that
> > I am specifying is thick enough.
> 
> My experience has been that liquid
> photo-imageable soldermask does a really poor job of covering vias.
There's
> no liquid in the hole, and therefore surface tension seems to draw back
the
> soldermask from the edges of the hole. I've had problems with shorts when
> I've used vias under SMT parts. 
> Steve Hendrix

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Re: [PEDA] Solder mask thickness (off topic)

[HxEngr]