[time-nuts] Vaperware Parts and pulse stretching circuits

[John Ackermann N8UR]

I know this is getting off topic, but one more comment from me.

Solder flux is really important.  I use nothing but "no clean" type for
SMT work -- very thin 0.015 no-clean solder (63/37 PbSn while I still
can), and a bottle of liquid no-clean flux with a needle dispenser.  I
make sure the work is wet with flux before I start, and add as needed.

Note that "no clean" isn't strictly that -- it leaves a residue, but it
is supposedly non-conductive and doesn't *need* to be removed.  But for
aesthetics, when I'm finished I dip the board into a bath of isopropyl
alcohol and apply a toothbrush.  Sometimes after that a distilled water
rinse is good if you're a perfectionist.  If nothing else, the cleaning
makes inspection easier.  (But use care... some components, like the
uBlox GPS modules, warn against immersion in any kind of liquid.)

John
----

On 4/25/20 12:00 PM, Burt I. Weiner wrote:
> John,
> 
> What you and I do for SMT type IC's is pretty much the same.
> 
> Several years ago the wife of a close friend was in the re-work business
> with a home setup.  What she taught me was to first line up one of the
> corner pins and tack solder it down.  Then do the opposite corner,
> center the pin and tack solder it down.  Do that with all four corners,
> taking care that the pins are properly centered before tack soldering
> them.  Once you've got the four corners properly in places, then go and
> center the remaining pins; depending on the size of the chip, this might
> require either a microscope or very pointy eyes.  Once all the pins are
> properly centered, flow solder over all the pins.  At this point
> shorting all the pins together is not a problem.
> 
> Once you've flowed soldered across all of the pins you need to slurp up
> all of the solder with a fine pitch SolderWick.  If done correctly you
> will wind up with all of the pins properly soldered and centered.  The
> next step is to remove and flux using Denatured Alcohol.  Once that's
> completed, inspect for any possible shorts or pins in the wrong place. 
> If all looks good, cover your eyes and power it up.
> 
> I have done the above one time on my own and to my utter amazement it
> worked!
> 
> Burt, K6OQK
> 
> 
> At 04:41 AM 4/25/2020, you wrote:
>> I do have a microscope (cheap Chinese unit, maybe $400 with
>> articulated arm and the works) and it does make things much easier. 
>> But as long as you can see the work, you can do the job. It's not that
>> hard to do small pitch parts.  I usually do the best I can soldering
>> individual pins, knowing their will be bridges, then clean up with
>> solder wick and *lots* of no-clean flux.  You can never have too much
>> flux.  I've found a 1.6 mm chisel tip is a good all around size for
>> SMD work, though I have a 0.8 mm chisel available for when things get
>> tight. The hardest part is getting the first couple of pins tacked
>> down so the part is square on the pads
> 
> Burt I. Weiner Associates
> Broadcast Technical Services
> Glendale, California U.S.A.
> biwa at att.net
> K6OQK
> 
> 
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