Date: Sun, 8 Jul 2012 13:25:15 -0700
Reply-To: neil n <musomuso@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: neil n <musomuso@GMAIL.COM>
Subject: Re: Digifant ECU: Corrosion? And.... Rosin or Heat Damage? PICS
In-Reply-To: <4ff9de66.0284cd0a.70a6.24e6@mx.google.com>
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Cool. The explanation and insights help.
Ok. So when one pops open their ECU, they aren't just looking for
failing solder joints due to time, use and heat (normal wear and
tear).
I had another look at your Picasaweb album here:
https://picasaweb.google.com/117189706757545167023/SolderFatigue
in particular this image:
https://lh3.googleusercontent.com/-YdpQ04ceKbs/TWxSLphU3nI/AAAAAAAAH4s/Ieu85LxefaY/s720/IMG_0556.JPG
That's a lot of crystalized (or crystalizing) joints. I had assumed
these were due to time/use/heat. If the saw process was used on
(some?) Bosch ECU's to cut leads, maybe this helped spur on poor joint
quality? (different solder introduced to manufacture process,
manufacture process not changed) Anyhow.....
A comment I recall reading in the archives. If one was certain, or
nearly certain that they were dealing with a poor or failing ECU
(solder joints), while symptom present or crops up, give the ECU case
a rap. If the symptom clears up or engine behaviour changes, this MAY
mean an issue with the ECU. The idea being that vibrations from the
"rap" may cause a better connection between the offending component(s)
and the PCB,
Caveat: I'm pretty sure I would know how hard a "rap" to use on the
ECU case but would caution that one chose to do this, they might want
to use something like the wood end of their small ball peen hammer and
"tap" the case.
Neil.
On Sun, Jul 8, 2012 at 12:24 PM, David Beierl <dbeierl@attglobal.net> wrote:
> 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
>
>
--
Neil n
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