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Author Topic: sound like a burnt chip?  (Read 1000 times)
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I hand soldered a 328tqfp and I'm afraid I have burnt it, I took a while to solder it, the first attempt with hot air it didn't line up so I jad to heat the whole chip to move it, it was working for a day and now only works when I apply pressure to the chip, I metered out all the pins and they all have continuity, it just gets me because it works for a while, I left and came back to do some more programming and now this, id just swap it out but I wonder if anything else could cause this? I have proper decoupling ( 0805 .1uf cap under the ic) as well as a 10uf electrolytic <1in away so I don't think its that
Unfortunetly the only output I can see without my oscope is the lcd, but if I press reset and wait a sec then press down on the ic its not one sec into the program
It won't program unless I press down either : /
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checking continuity with a meter has a drawback, you press down to make contact, have you gone in with a light touch, exterting little to no force on the pins as you check?
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If pressing down gets the thing going, it's quite unlikely you burnt it.
Try to figure out some way to press the part down without putting any force on it sideways, and reheat it.
You'll probably fix it that way.
Anyway, nothing to loose, right ?

Next time you have to solder parts like these, you might consider glueing them to the surface.
Use some glue which can resist heat, doesn't glue instantly so you can adjust / align it and can be removed when needed.
So some silicone based glue would come to mind.
Use a very small amount of glue ofcourse and wait for it to settle before you start soldering.
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Have a look at "blink without delay".
Did you connect the grounds ?
Je kunt hier ook in het Nederlands terecht: http://arduino.cc/forum/index.php/board,77.0.html

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Almost certainly a dry/cracked joint. Apply flux around all the pads and touch up each one carefully with a fine tip soldering iron. Usually only about 1 second of contact per pad is enough to reflow the solder and cure your bad joint. I do this working under an illuminated binocular microscope that makes spotting and correcting bad joints very easy.
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Almost certainly a dry/cracked joint.

Agree.
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I think it was pretty light contact, some I wasn't sure because some flux residue seemed to be in the way, I used the solder blob method and wicked away the excess hopefully that was it, I have a spare but resoldering them isn't too fun
Ill test it after work today
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Good luck on soldering fine-pitched smt parts. What I would do is set the chip down,
and solder a couple of pads by hand first, in order to get the pins all aligned.

Also, some people swear by just blasting all the pins with solder [manually], and
then using solder wick to draw off the excess solder that's bridging across adjacent
pins. You could use the same method to resolder any bad joints.
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Quote from: oric_dan
Also..

Didn't he just tell he did that and is going to test the result later today ?
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Have a look at "blink without delay".
Did you connect the grounds ?
Je kunt hier ook in het Nederlands terecht: http://arduino.cc/forum/index.php/board,77.0.html

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oh, yeah.
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Well that fixed it! Apparently the multimeter was just enough pressure to make contact somewhere, but it works fine all the time now without any pressure applied, and yeah hot air works perfect for small stuff with like soic8 and 0805,1206 stuff but for the 32tqfp it just didn't work out as well, lesson learned
And lol ill be one of those who swear by it because it just worked lol
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Quote
and yeah hot air works perfect for small stuff with like soic8 and 0805,1206 stuff

I find hot air to be a royal pain on soldering much of anything, I use it quite a bit to remove stuff, but once you get the hang of it, doing a 603 with an iron is not much trick  smiley
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Always use IC sockets. They are easy to solder and at the same time easy to replace burnt ICs.
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Sockets for surface mounts TQFP parts aren't practical, or inexpensive.

I use a nozzle for TQFP parts to ensure all legs are heated together.  With a fine tip iron and small diameter solder, its also possible to touch up individual pins that didn't get sufficient solder paste initially.
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Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

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I can do them with a big blunt hackko chisel tip, the magic trick to that is to use solder paste with an iron, and wash off the boards once your done (alcohol + horsehair brush, check the welding section at your hardware store ~50 cents a pop)  ... at home I have a pretty fine point conical, and use thin (wire) solder.

Theres always more than one way to skin a cat, I just dont like hot air cause unless you have the perfect nozzle its a big risk on multipin parts, and no matter how many of the pricy things you have, it always seems like you need yet another one for a package you have not soldered yet

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I measured packages and then ordered a bunch of sizes from mjpa.com
http://www.mpja.com/nozzle
enter nozzle & search, brings up quite a list.
I have used 3 for FTDI chips and, 328s, and 1284s so far.
Really nice having all pins ready at once after maybe 30 seconds of hot air application.
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Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

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