Soldering Question...

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Hydroid

Senior Member
Hi all,

Have a question about soldering surface mount chips. I bought two CAT4016 - 16 Channel Constant Current LED Driver chips to play with. I didn't realize however, how small these things are. The chip is a 24 pin TSSOP footprint. Actual chip measures 4mm X 8mm. I successfully made up a PCB using Diptrace and transferred it to a photo sensitive double sided PCB. The board came out great despite my trepidation about 0.01" traces!

This morning, after my coffee and some deep breathing, I dove in and actually soldered it up. Took about 45 minutes with X20 head mounted magnifier - My head was so close to the board that I could feel the heat off the soldering iron. Even my finest tip seemed huge under the magnification. I couldn't get each individual trace without some bridging and had to use my desoldering pump iron to suck away the excess. I hooked it up to an 08M, input some code and actually have the 16 LEDs strobing ! I love it when a plan comes together...

Figuring there must be an easier way, I did a google search and found this:

http://www.youtube.com/watch?v=MSIyxEUK8Fo

That chip looks to have double the spacing between pins of mine (similar to the surface mount 28X1's I have), but I'm wondering if it's actually as easy as he makes it look.

I can't say I've ever seen flux-in-a-bottle, but then again I've never really been looking for it either. Is this something that's readily available ?

I've seen the examples with the solder paste and ovens and such, but would prefer to stick with the soldering iron route.

Any golden tidbits of advice to be had by the 'gurus' here - other than "Stick with larger chips" :)

Regards, John.
 

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John West

Senior Member
My web connection today is too poor for me to review the PDF.

However, I always just "blob-solder" all the pins, then use solder-wick to draw off the excess. Surface tension isolates the connections from one another and leaves nice clean connections.

I've never needed to add extra flux, but I can see how that could help prep the pads.
 
H

Haku

Senior Member
From demonstration videos, written explanations of people's own experience and my own experience of SMD soldering it appears there's several different ways of doing the job, which way is best is the way you discover is the easiest.
 
H

Hydroid

Senior Member
Thanks !

Thanks guys.

I have never used solder wick in my life - I always thought it was just for desoldering - and I have a desoldering iron that does a great job. That tip about flooding with solder and then 'sucking-up' the excess worked quite well. I re-worked my small chip and the connections look quite a bit better too. About 5 minutes vs 45 was a nice touch as well.

That video link was excellent. I'll have to pick up some flux - and some thinner solder - and give drag soldering a try. It looked quite easy and fast, but I'm sure he's done it often and there's experience involved in a quality job.

As stated, I guess personal preference is key. Go with whatever works :)

Thanks Again !

Regards, John.
 
premelec

premelec

Senior Member
If you have some solder bridges - by mistake or intentional flooding - you can chase the bridges clear while the solder is hot with a wooden toothpick - I use flat ones and a bit of solder and the out gassing from the wood does wonders... solder wick actually removes solder and you can fake it with shield braid from coax in a pinch. There are lots of liquid fluxes of various sorts around and you can even make some by dissolving rosin in ethanol - old style stuff but smells nice and works OK many times...
 
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Minifig666

Senior Member
I just found this guy on MyTube and he seems to know what he is doing. Solder on one pin by pre tinning it. Mount the board at 45 degrees, add lots of flux and rub on some solder.
Jump to about 1:00 to observe him, but you don't need to watch the whole thing.

He has serious skill...
 
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John O

Senior Member
He certainly makes it look easy! Wonder how it would work on home made PCBs without the solder-resist?


John.
 
J

John West

Senior Member
One further comment about this sort of work - use fresh solder (or solder paste) of high quality, i.e. not some unknown material that has been lying around for years and years. The flux core (or paste) will deteriorate with age and lose efficacy.

In production environments such materials get used up quickly enough that aging isn't a problem. In hobby work, it is.
 
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