At 03:07 PM 7/8/2012, neil n wrote:
>the archives re: Bosch ECU's and sloppy (my term) solder work.

Not sloppy.  They cheaped out on their alloy (I think) for the wave
soldering process, leading to rough, crystallised-looking joints.  At
any rate, something wasn't right on the wave line.  The bright shiny
ones were hand soldered with 60/40 or 63/37 tin-lead solder.

>  Good to
>get a better handle on the difference between an actual heat mark and
>solder work. Those spots looked like leftover rosin to me.

That's exactly what they are.

In the wave soldering process the boards are on carriers.  They enter
the machine and are preheated by infrared, then pass across a "wave"
(actually a linear fountain) of (usually rosin) flux and then a wave
of solder.  Then they're de-fluxed by vapors and/or liquid cleaners,
and in some cases (techs hate these) the leads are trimmed off by a
circular saw which leaves nasty sharp burs on every lead.  Components
which can't stand the wave process are now hand-soldered on, then the
boards go to test.  Ones that pass go to burn-in; ones that fail go
to re-work.  Normally in production I'd expect that hand-soldering
flux would be cleaned off, but it varies.

Yours,
David