I've seen the same problem from wave soldering the bottom side of smt.
Glue is probably curing too rapidly and is causing some air pockets
underneath the component. When it goes through wave, solder is getting
trapped in those air pockets causing a short. Also, check the DOM on the
glue that you're using. Make sure the it is still within the
manufacturer's listed shelf life.
Tom
At 12:42 PM 11/1/00 -0500, you wrote:
>I've seen it also, but not from wave solder. It usually happens when you
>print paste and then glue. When you reflow the paste and cure glue at the
>same time, you get solder paste trapped in the glue, causing a short. Check
>some parts right after reflow, you may find your problem. An xray can help
>here.
>
>-----Original Message-----
>From: Trevor Goddard [mailto:[log in to unmask]]
>Sent: Wednesday, November 01, 2000 12:08 PM
>To: [log in to unmask]
>Subject: [TN] solder under chip components
>
>
> Has anyone ever seen solder shorts under an smt resistor that has been
>glued on a board and then wave soldered?
> The boards go through the standard surface mount process of screen printing
>the glue, placement of components and curing the glue. Then the boards
>receive solder reflow for the top side of the board, on to hand assembly and
>then wave solder. During all in process inspection even after wave solder,
>the boards look good. When the boards get to test it is a different story.
>Randomly across the bottom side of the board, the side that was wave
>soldered, we will get short conditions on various caps and resistors. If you
>look at the component nothing appears to be wrong, but when the component is
>removed you can see solder on the under side of the component and on the
>pcb.
> This problem has just cropped up, so I find it a complete mystery.
>
>Thanks in advance.
>
>
>Trevor Goddard,
>SMT Supervisor
>XLTEK
>(905) 829-5300 x 348
>[log in to unmask] <mailto:[log in to unmask]>
>
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