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December 2005

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Subject:
From:
Ingemar Hernefjord <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Ingemar Hernefjord <[log in to unmask]>
Date:
Mon, 5 Dec 2005 11:24:21 +0100
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text/plain
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Remember the production stop and the unique veils and crystal on the
boards?
This came to me from the guy who was invited to help us solve the
problem.
(a 'casette' is a PWB mounted on a metal cooler with channels for forced
air circulation)


> The lacquer problem is solved. I believe that the crystal
> on lacquer surface is salt from our cleaning system. The cleaning
> agent Vigon in the system normally has a solid content 0.5%. The BFB
> cassette, after machine cleaning, still remained a pretty amount of
> Vigon on inside. It is also very common that the cassettes are often
not
> completely dried before being lacquered. The salt within Vigon left
> inside cassette is believed to have diffused to the surface of lacquer

> following the water/moisture migrations. When water moleculars
> evaporated, the salt left on the surface form crystals. This
> assumption can also explain why the crystal patterns are always
> initiated at short edges of the cassette, where the moisture content
> is normally slightly higher because the water absorption is more
>pronounced along the edge of boards. Recommended not to use Vigon.
>
> With best regards
>
> Qiao Wang PhD


So, as many of you suspected, the higly alcaline Vigon200 was the root
case, or rather the cleaning machine maintenance. Thank you all for good
advice.

Ingemar Hernefjord
Ericsson Microwave Systems

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