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Yet another resistance decade box

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johnmx:
Fortran, in order to prevent shorts during soldering I recommend you to make tented vias next time (no solder mask opening).

ez24, if you have a short circuit you can desolder the resistor (keep heating both sides 1s at a time until the resistor gets loose), remove the excessive solder on the board with solder wick and solder the resistor again.

ez24:

--- Quote from: johnmx on July 29, 2016, 09:40:00 pm ---ez24, if you have a short circuit you can desolder the resistor (keep heating both sides 1s at a time until the resistor gets loose), remove the excessive solder on the board with solder wick and solder the resistor again.

--- End quote ---
I will try this if I run out of boards. 

Did another one today successfully but ugly. The problem I have is leaving "whiskers" when I lift the iron.  I always have to go back and try and level them.  Sometimes I can and sometimes I cannot.

I have a question: what do people do with the standoffs?  When I started, I trimmed off all three, then I tried just the center, then I tried not to trim any.  Without trimming any I got the board out ok but I could not get the new one in.  In fact I destroyed the switch trying to get it in.  So I went back to just trimming the middle one BUT it seems the middle one is the most important to keep the switch wipers touching the board.  Just curious on what others are doing.

When I am done and before I assemble them, I think I will take a hot needle and press down in the center of the ones that I cut to make them spread out a little.

Vias
It seems to me, with a 10x glass, that the vias at 2,7, and 9 are actually touching the pads, whereas in the picture they do not.  I am afraid to test with a meter because if they are not touching, the probe would probably make it contact (it is that close). I try very hard to keep solder away from the via and it seems to work.  Comments ?




Fortran:
Whiskers can have a few reasons.
Heating too long burns away the "wetness" and solder clings instead of flows.
Is your tip clean?  It should be silvery and shiny.
If it is..  have you tried adding flux?
If it still won't cooperate.. try a different/better solder. The cheap stuff is usually a nightmare to work with.
What's the dia on your solder? It might be too thick and that's no good either.


Standoffs:
You only need to cut the two. Use a scalpel or box-cutter to cut them flush to the board.

The vias on 2, 7 and 9 are connected to those pads, so a short there does nothing :)
It's only the one under 3 that's a potential risk of shorting.

ez24:
Whiskers can have a few reasons.
Heating too long burns away the "wetness" and solder clings instead of flows.

--> I do not think this is the problem, I do not spend much time on the pad

Is your tip clean?  It should be silvery and shiny.

-->  Yes I clean it each time I use it


If it is..  have you tried adding flux?

--> I will order a flux pen, I do not have any


If it still won't cooperate.. try a different/better solder. The cheap stuff is usually a nightmare to work with.

--> I use Dutch Boy, I think it is good  (but very old maybe 50yo)   I will order some new solder - Kester
https://www.amazon.com/KESTER-SOLDER-24-6040-0027-Stand-Diameter/dp/B00068IJPO/ref=sr_1_7?s=hi&ie=UTF8&qid=1469859605&sr=1-7&keywords=rosin+core+solder

What's the dia on your solder?

--> Very small, my guess .5 mm  The Kester is .031", which sounds very small to me


It might be too thick and that's no good either.


Standoffs:
You only need to cut the two. Use a scalpel or box-cutter to cut them flush to the board.

--> now that I think of it, it is probably better to cut the pair and leave the center.  I will try that on the next one

The vias on 2, 7 and 9 are connected to those pads, so a short there does nothing :)
It's only the one under 3 that's a potential risk of shorting.

--->  :phew:  this will help a lot. I was trying very hard not to get solder near the edge of the pad

So far I have done 3 good ones and 1 bad one  :-+   Not bad for an old fart.

thanks a lot - this will help

Fortran:
Yeah that might be it.
Solder usually have an expiration date. It's probably fine a decade or so after that, but still. If it's 50 years old it wouldn't harm to try a fresh one.
I've never used Kester, but from what I've heard it's good stuff.
0.031" is about 0.78mm.  That's quite thick for SMD.
I'd go for 0.5mm or smaller just to have better control over the amount of solder you're putting on.

If you want to I can send you some 0.3mm, 0.5mm and 0.7mm to compare.

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