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June 2000

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Subject:
From:
Kiiski Jarmo <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 1 Jun 2000 13:44:52 +0300
Content-Type:
text/plain
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text/plain (82 lines)
A story about blowholes.

Years ago we had blowholes in our FR4 double-sided PTH boards after wave
soldering. We knew that it is the vaporized water that makes the blowholes.
And we thought that if there was no water in the boards to vaporize, there
would not be any blowholes. So we baked the boards before wave soldering.
But we were not satisfied with the results and with the time and floor space
that the baking took. Also I had a hunch that what we were doing was more
like going around the problem than trying to solve it. So I made some
cross-sections to the PTH's that had blowholes and I found holes in the
plating and very thin plating in the holes. Next we purchased a meter
(Caviderm) to measure the plating thickness in the PTH. With the meter we
get the thickness of the plating in the PTH without destroying the board and
used it (and we still use it) in our incoming inspection of PCB's. As a
result the blowholes disappeared.

We had blowholes because of thin copper plating in holes and because of
holes in plating. When water vaporizes it requires more space and when there
is no space inside the board, the pressure increases. If the plating is thin
(or there is hole) the vaporized water can come through the plating and
pushes the molten solder away causing the crater like blowhole to solder
joint.

By measuring the plating thickness in the incoming inspection we were able
to control the quality of the PTH's and we don't need to bake the boards
anymore and we don't see blowholes anymore.

B.R:
Jarmo Kiiski

> -----Original Message-----
> From: Martin Christie [SMTP:[log in to unmask]]
> Sent: 1. kesäkuuta 2000 11:48
> To:   [log in to unmask]
> Subject:      [TN] Baking of boards
>
> Hi Technetters,
>
> What is (or where can I find) the recommended bake parameters for baking
> boards before reflow?
>
>
> Martin Christie
> ACW Technology Ltd.,
> Hylton Road,
> Petersfield,
> Hants.
> GU32 3XX
> Tel: 01730 300000 ext 146
> Fax: 01730 266045
> e-mail: [log in to unmask]
>
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