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Soldering
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Please be positive and constructive with your questions and comments.

Soldering

by digitaladdictions on Tue Dec 01, 2009 12:28 am

Got my PCB today and most of the components. I have to wait a month for some of them to come in. Just curious how most of you assembled yours. Solder it by hand with an iron and regular solder? Solder Paste? Hot Air? Reflow Oven/Skillet? I have only done touch up work on SMT so this is new ground for me. I bought solder paste and I'm getting a hot air rework station for Christmas (about the time the rest of the parts come in).

My instinct was to paste and reflow but being I have never done that before I was confused on how that would work with a double sided board and looked at what ladyada did and it appears she did it by hand with a soldering iron.

Also the board has a thin layer of something over the copper. I would of thought that should be removed before soldering to ensure a good electrical contact but also looking at the pictures from the Make section it appears ladyada did not.

I do have a temp controlled soldering iron with a real fine point tip so I probably could do it by hand but it just kind of surprised me that that method would be recommend and not met with a "your nuts"

Anyways just curious; I have to wait a torturous month for the remainder of the parts so I have time to think of these things.
digitaladdictions
 
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Joined: Tue Nov 24, 2009 4:44 pm

Re: Soldering

by dnewman on Thu Dec 03, 2009 12:39 am

Something over the copper? Without a picture, it's hard to tell what that might be. There's three likely
things:
1. A silvery appearing stuff: that's there to prevent oxidation of the otherwise exposed copper. Depending upon the production process for the board, it may have been placed as a resist over the copper to prevent it from being etched away.

2. The soldermask (often a green semi-transparent coating). You don't want that over the pads as it is there to prevent solder from adhering to copper. Soldermask comes in a variety of colors, but green is the most common.

3. The silk screen printing: another thing you don't want over copper you will be soldering to.

As to best technique, I do these things myself by hand with a fine tip, good light, a magnifier of some sort, and plenty of solder braid. Doing the hot plate method only works well when you place ALL the parts you will be soldering with the hot plate at once. Otherwise, you are repeatedly cooking some of the parts. And, of course, placing SMDs on both sides of the boards doesn't work if you're going to use a hot plate for both sides.

To get started training try something simple like SparkFun's SMD/SMT kit (a Simon game with an ATmega168). You'll want to have a 6pin ISP programming header in order to program the device after you've built it -- one is not included in the kit but the board has pads for one.

There's a couple of interesting SMT/SMD videos I've seen on YouTube. Look for videos from Curious Inventor (e.g., Surface Mount Soldering 101). Therein, you will learn the utility of solder braid when soldering fine pitch SMDs.

Dan

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Re: Soldering

by digitaladdictions on Fri Dec 04, 2009 11:38 am

"A silvery appearing stuff" that would be the stuff. I will leave it be then. It just looks kinda sloppy as there are hair line scratches in it everywhere.

I used barebonespcb.com since I was able to get the Antenna, LiIon, and Main boards for $67. 4pcb.com would have cost $350 for the same thing with solder mask and silkscreen. Granted if I ordered 10+ the per set coast would have significantly dropped but I did not need 10+ and did not want to try selling them. So there is no solder mask that would either have covered or replaced the "silvery appearing stuff" that I'm not use to seeing.

I had watched some youtube videos. Looks like for the passive stuff I will use a soldering iron and for and some of the heat sensitive ICs put the paste down preheat it with hot air and then place the part to avoid overheating it.

As far as the solder braid method I discovered that one all on my own 8 years ago or so back in my electronics engineering associates degree when I could not even manage to solder a dip package without bridging pins :oops: . Luckily that is not a problem anymore.
digitaladdictions
 
Posts: 15
Joined: Tue Nov 24, 2009 4:44 pm

Re: Soldering

by dnewman on Fri Dec 04, 2009 1:19 pm

digitaladdictions wrote:"A silvery appearing stuff" that would be the stuff. I will leave it be then. It just looks kinda sloppy as there are hair line scratches in it everywhere.

That's normal. The tinning material is fairly soft and scratches very easily during manufacturing. It can also telegraph through any serious scratches in the copper underneath.

FWIW, I got my boards from aqisnotliquid. See his post under "WB_1.0b Boards for Sale".

Regards,
Dan

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Posts: 15
Joined: Fri Nov 13, 2009 5:50 pm

Please be positive and constructive with your questions and comments.