Re: gEDA-user: OT: soldering QFN packages with exposed bottom pad?

[Bob Paddock <bob.paddock@xxxxxxxxx>]

On Sat, May 2, 2009 at 3:19 PM, John Griessen <john@xxxxxxxxxxxxxx> wrote:
> Bob Paddock wrote:
>
>> Our CM got a ten minute rant from one of the Big Name Solder
>> Vendors when they were asked that question.  After ten minutes
>> our CM knew all of the evils of QFN packages, such as being
>> almost impossible to clean under (don't use QFN packages in
>> high impedance circuits, which is giving us fits right now,
>> due to poor cleaning), but still the Big Name Solder Vendor did not answer
>> the question as to what *should* be used.
>
> So BGA packages wash out underneath effectively?

Only slightly better, depends on the size of the package.

Ever consider how well stuff gets cleaned from under even  a simple
0603  resistor that is flat on the board?

It also makes a difference to the type of cleaner being used,
such as Batch Cleaner, which is a glorified dishwasher, or some
thing like a Injection Cleaner too.

Most flux is active for a only for a short time and it is designed
to be burned out by the soldering process when you get your profiles
correct, so it presents little problem.

The problem comes when the flux residue starts to hold moisture
or ionic contamination.  In a high impedance circuit or RF tuning
this start to become a real problem with the circuit operation.

Problem is showing up more often as we get deeper into low power
systems, such as Energy Harvesters.  If you are only getting 1 mA
you don't want to see 100uA wasted to leakage.

If you want to get into extreme circuit areas for leakage problems
look at the AD515,
AD549, and TI OPA128 electrostatic grade op-amps.

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


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