From: Chuck Simmons
Organization: You jest.
X-Mailer: Mozilla 4.61 [en] (X11; U; Linux 2.0.33 i586)
Subject: Re: having SMT components mounted
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Date: Fri, 04 Oct 2002 05:38:21 GMT
NNTP-Posting-Date: Thu, 03 Oct 2002 22:38:21 PDT
The little lost angel wrote:
> On Thu, 03 Oct 2002 23:07:23 -0400, "Michael A. Terrell"
> > The paste contains solder and flux. It is applied to the pads, then
> >part is placed. When the board and components are heated in the reflow
> >oven, the solder melts, the flux cleans the pads and pins, and then, if
> >all goes well, you only have a small amount of flux residue to remove
> >after the board cools.
> Ah, so this could be used instead of normal soldering even for non-SMT
> parts? I mean it sounds a lot easier to spread some paste on the pins
> and popping it into a preheated toaster oven.
It sounds good but when we send out for hand assembly, the vendor does
not do that. After all, if I have a low yield part (I have had some that
yielded at about 5%), the vendor better not abuse a part that I blessed
as good after hours of testing binning mainly into the circular file.
Anyway, our evaluation boards have components on both sides. IR process
is all that will do if you insist on using solder paste. There is one
board that I do that is a special for various test devices. The board
has one or more (depending on hardware type) 0.5mm pitch ZIF connectors.
The connectors melt if you heat the body to soldering temperature. No
solder paste and toaster ovens for those turkeys. I also freely mix
through hole and SMT. This is problematic for soldering processes in
that no single process will do the job except hand soldering.
The last board I wrestled with (single proto of a new board) has 5
prototype parts with 100 or more pins each (up to 208 pins) 4 of which
were blind packaged (untested wafers). Pure nightmare. Don't even talk
to me about putting that board in an oven. It took me a full day to
bring the board to life after delivery (I'm getting much faster as time
goes on - it used to take me three days for a new board with multiple
proto blind packaged ICs).
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons email@example.com