Re: gEDA-user: "soldermask via caps"

[Bob Paddock <bob.paddock@xxxxxxxxx>]

On Fri, May 21, 2010 at 7:28 PM, DJ Delorie <dj@xxxxxxxxxxx> wrote:

>  Then put some flux on them...

Along with the soldering issues, always make sure there is a path for
the flux to be flushed out from under parts after soldering.

Leaving it there leads to high leakage currents, we have seen over 100
uA from trapped flux, which is unacceptable if you want to device to
run from something like a coin cell.

It can also destroy the parts after some period of time.  The period
of time depends on how aggressive of flux is used.  Could be hours for
the aggressive lead-free flux, or years for the common mild flux.

Back to the original issue of under the part via..  A large one makes
sense for a hand assembled prototype.  It is not want you want for
Contract Manufacturing production runs.  The large via can tend to
thieve solder away from the pad so the via gets soldered filed, but
the pad does not soldered.

An even board heat from hot-plate or toaster oven over the whole board
is general a better approach.

Along with ESD we need to start paying more attention to Moisture
Sensitivity Levels, MSL ratings in the datasheets.
As parts get smaller even minuscule amounts of moisture can turn to
steam fracturing parts as they are heated if they heated to fast.
The plate/oven approach allows more control over a long term ramp up,
and ramp down.


Like all things in this field the answer is usually "it depends"...

-- 
http://blog.softwaresafety.net/
http://www.designer-iii.com/
http://www.wearablesmartsensors.com/
http://www.unusualresearch.com/


_______________________________________________
geda-user mailing list
geda-user@xxxxxxxxxxxxxx
http://www.seul.org/cgi-bin/mailman/listinfo/geda-user