Mail Archives: geda-user/2012/01/02/14:11:52
Hi all --
>> Would you say it takes a little bit of practice to get this working?
>> That is to say, before this works well should I expect to fubar
>> boards? Solder bridges and splashes are not a problem - but
>> destroyed traces are. I can probably obtain a number of random
>> unused boards for experimental purposes. Maybe that makes sense
>> before jumping in with my new board - it would really ruin my day if
>> the board got destroyed.
>
> The only time I damaged a board with this technique was when I was
> doing more than one board in a row, and didn't let the hotplate cool
> between boards. However, the result wasn't a broken trace, it was a
> charred PCB that *still worked*. You're not going to get anything hot
> enough to melt copper.
I built a SMT soldering plate a few months ago based upon what I have
seen DJ (and others) do. I attached a flat 6"x6" Alu plate to the top
of a cheap hot plate. I drilled a hole in the side of the Alu plate,
and insert a thermocouple in the hole to monitor the plate temp. I
use PbSn solder paste which I squeeze onto the SMT pads, place the
components, then ramp up the temp until everything reflows. Then I
quickly remove the PCBs and place them on a glass or metal surface to
cool down.
Here are some observations from me about this process.
* If you're going to solder only low-profile components (i.e. small
passives, SO-8s, etc), this technique works passibly well. You need
to practice a few times on scrap PCBs in order to know what to
expect. Don't waste your good boards on this practice.
* I have had bad luck with tall components, such as electrolytic
caps. These components seem to suck up heat, preventing the solder
paste on their pads to melt. Meanwhile, all the other components
are swimming in their melted solder, and the devices cook while
waiting for the solder to melt under the large components. My
advice is to use through-hole parts for the large components which
can act as heat sinks, and manually solder them after you have
reflow soldered all the small components.
* I find it difficult to squeeze a reasonable amount of solder paste
out of the syringe. Therefore, I tend to put too much solder paste
onto the pads, and need to touch up the board with a soldering iron
and solder wick afterwards. Maybe others with more finesse don't
have this problem. I suppose practice will help with this
problem. Alternately, you can get a stencil and use it to control
the amount and placement of your solder paste.
* In light of the above, my practice nowadays is to only use the
solder plate for parts which absolutely require reflow soldering
(e.g. parts with underside solder pads). It's just as easy
for me to hand solder all the other parts, and the process is
better controlled.
Just my observations....
Stuart
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