Steve,
I'm guessin, as usual, but my theory is that more frequent cleaning is required at slower print speeds
because of the increased time that pressure is applied to the paste in the apertures during printing.
Slower print speeds give more time for the aperture to fill up, but also more time for paste to extrude
between the stencil and the PWB. I have also noticed this tendancy when printing SMD adhesives.
Gary Camac
Stephen R. Gregory wrote:
> In a message dated 2/23/99 9:42:59 AM Pacific Standard Time,
> [log in to unmask] writes:
>
> << we are getting good gasketing. We ended up with a squeegee speed
> of 1.5-1.6 in/s (or about 40mm/s)when we were printing boards with one
> 20-mil QFP, among various other larger-spaced parts. We had originally been
> at 0.6 in/s (about 15 mm/s)and having to wipe the stencil every five passes
> to get the stencil to release the paste on the QFP aperatures. We then
> tried 1 in/s and finally 1.5 in/s. At these speeds, the stencil had to be
> wiped once out of one hundred passes (for boards with more 20-mil parts I
> may slow it down). Good enough for me, and the operator had no complaints.
> Now we are ready to run! I just wanted to thank everybody for this, and
> past, advice and let you know how it turned out!
>
> Ryan Jennens
> TelGen Corp.
> >>
>
> Hey Ryan!
>
> Glad to see things working for you...but ya' know, when I read your
> email, I have to admit a little confusion. I don't know if I'm the only one
> who's ever been taught this, but I've always understood that the slower the
> squeegee speed the better when it comes to printing fine pitch.
>
> Back when I first started using metal squeegees, I talked to a gentleman
> named Mark Curtain who worked at Transition Automation to get his opinion on
> how we should go about setting-up the printer to use them, if I needed to
> change my stencil spec's, and stuff like that. I remember him telling me that
> there was 3 things I needed remember about squeegee speeds; 1). The slower the
> better, 2). The slower the better, and 3). The slower the better. (sounds like
> he was trying to make a point, huh?)
>
> Don't get me wrong, I'm not about to question your success with what's
> working for you, but I'm just trying to get a grip on why a faster squeegee
> speed cuts down on the how often you'll need to clean your stencil. Do ya'
> have any sort of theories why that would be? You know how us engineers
> are...always questioning sumthin'...
>
> Thanks Pardner!!
>
> -Steve Gregory-
>
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