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September 1999

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Subject:
From:
Doug Black <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 23 Sep 1999 09:12:00 +0100
Content-Type:
text/plain
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text/plain (101 lines)
The aspect ratio between stencil aperture width and stencil thickness is the
most important factor in stencil production. A factor of 1.5 times the
thickness of the stencil is applied for aperture width.
i.e. On a 6 thou (150 micron) stencil the minimum aperture recommended would
be 9 thou (225 microns).
The release of the paste from the aperture can also be dependent on
seperation speed of PCB from the stencil and also the paste type (particle
size being used).
If you wish to discuss your particular application in more detail please
feel free to contact me off line.

Doug Black
Technical Manager
Dek Precision Screens Division
Weymouth, England
Tel: +44 (0)1305 760909
[log in to unmask]
 ----------
From: Taheri, Kamran
To: [log in to unmask]
Subject: Re: [TN] Need to know
Date: 22 September 1999 18:37

I don't know what kind of printer you are using. But, usually the board
pulls away "snaps-off" from the stencil. What type of stencil are you using?
Do you have a slow snap-off option in your printer?

> -----Original Message-----
> From: Steffen, Don E [SMTP:[log in to unmask]]
> Sent: Wednesday, September 22, 1999 12:24 PM
> To:   [log in to unmask]
> Subject:      [TN] Need to know
>
> Technetters
>
> I have a situation where I need the advice from the Technetters. I have an
> assembly with HASL. In order to stay within the aspect ratio guidelines, I
> must use a stencil that has a .0085 aperature opening, a 20 mil spacing,
> and
> I must use a 6 mil stencil. I tried this and when the stencil pulled away,
> the surface tension pulled away the solder paste from the pad area. If I
> were to go to a 5 mil stencil (which is outside the Aspect Ratio
> guidelines), would this help me with keeping the solder paste on the pad
> and
> not on the stencil? Or is there another approach that I should consider
> instead of going to another stencil thickness? Any help you can give me
> would be appreciated
>
> Donn E Steffen
> Senior Quality Engineer
> VDO Control Systems
> Auburn, IN 46706
> Phone (219)925-8887
> Fax (219)925-8710
> Email: [log in to unmask]
>
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