Thanks to both you and Joyce for the advice. Since I have lots of big parts
on this one maybe the answer is a stepped stencil.

Wayne T.

On Thu, Apr 23, 2020 at 10:37 AM Robert Kondner <[log in to unmask]>
wrote:

> Wayne,
>
>  I would try a thinner stencil foil first. It would help with release on
> small apertures and reduce the problem with too much paste.
>
> We use a MY600 paste printer (solder jet printer) and at .4mm it does not
> have "Perfect Prints". I have never seen perfect prints a .4mm. But there
> is less paste between the pads and it helps the paste to reflow evenly onto
> the pads. With continuous strips of paste across the pads you don't get as
> even divide of solder reflowing to each pad.
>
> I would try 2 or 3 mil foils first.
>
> Bob K.
>
> -----Original Message-----
> From: TechNet <[log in to unmask]> On Behalf Of Wayne Thayer
> Sent: Thursday, April 23, 2020 1:05 PM
> To: [log in to unmask]
> Subject: [TN] QFP stencils
>
> Hi Gents-
>
> I just did a prototype for a fairly simple board which had reasonably
> sized parts. Several 0402's and everything else was significantly larger.
> Except....
>
> Except for a 100 lead 0.4mm pitch QFP. Based on most of the parts being
> pretty sizable, I selected a 125 micron stencil. I found I could get solder
> down into the apertures for the QFP, but it was WAY too much solder, and it
> was clear that if I made the apertures any narrower, they wouldn't print.
> Also, with the 125 micron deposit, the deposits tended to short together
> anyway with that pitch.
>
> I recall from somewhere that I saw someone use apertures that went
> crosswise to the QFP leads, so a QFP would only have 4 apertures, shorting
> all of the pins together. But my recollection is that still worked because
> surface tension pulled the solder deposits away from each other. (I'm sure
> you have to make sure the volume is not on the high side, which would
> result in shorting.) But when I searched for advice on QFN apertures on the
> web, nothing came up on this.
>
> Anyone with helpful experience in this area?
>
> Thanks,
>
> Wayne Thayer
>
>