LQFP48 - 48-pin, 7 x 7 mm Broken pins repair

[lordvader88]

I fried a STM32F103C8 microprocessor once, and bought some replacements. I'm very very new to SMD soldering, and broke some pads and have a few on the verge, getting it and new ones off...on/off/on .

So now I have a chip almost on there with 2 jumpers instead of pads. But then I broke the 2 pins off the chip, it's 2 right next to each other, at least on the edge though. Kept soldering them together. .

So I'm chipping away at the plastic to get enough to solder to, and that's not going well, should have enough but I need a third hand for my 30x mag. loupe.

Just wondering in general how far in the pins go ? I'm sure it's not like a TO-92 with the leads going right to the die. Maybe 1/2mm or 1mm ?

[Jeroen3]

With an QFP48 you might be dissapointed.
However, it will depend on the size of the die and the lead frame used. An STM32F103 might just fill the QFP48, since you can't get it smaller. Only the QFN 36, which is basically the same plastic size, without leads.

(source of image: http://www.prioritylabs.com/engineering-services/x-ray/)
Image is not an STM32F103.

[Mechatrommer]

So I'm chipping away at the plastic to get enough to solder to, and that's not going well, should have enough but I need a third hand for my 30x mag. loupe.
Just wondering in general how far in the pins go ? I'm sure it's not like a TO-92 with the leads going right to the die. Maybe 1/2mm or 1mm ?

i know this technique, but to avoid further wasting time in the future, i suggest you get a descent heat gun and necessary stuffs for smd soldering ie solder flux and braid. ymmv.

[Ian.M]

I can understand FUBARing some pads, and occasionally FUBARing a pin if transplanting a chip from one board to another, but *HOW* did you manage to break two pins off a new replacement chip, even working with grossly inadequate tools?

Generally, removed SMD parts go in the dustbin.  An exception may be made for salvaged parts, that are difficult or impossible to replace with new, but transplanting a chip more than once isn't advisable.  If the chip is so valuable there is no realistic alternative to reusing it repeatedly, then you need the proper tools, equipment and consumables + a tech with a lot of SMD rework experience.  If you don't have that, then you'd better put it on a carrier board or otherwise socket it. 

If your skills and equipment are on the slim side, a ChipQuik low melting point alloy SMD removal kit (for Sn/Pb or Pb free according to your board) is your friend!

[lordvader88]

Yeah I'm looking for a diesel engine glow plug to make a free ghetto hotair gun, the sooner the better.

Yeah I bent both pins upwards, and then just moved them too many times for reasons IDR besides soldering them together. Time to try again with some more soldering experience since 2 months ago. And using something better to hoild the jumpers in place. The pins are super close together at the epoxy, I couldn't get them so far, not both anyway, and gave up.

I'm using lots of flux. The main problem was trying to get the solder off and stop it webbing. I have copper braid. If this fails I doubt 1/2 the other pads with survive.

But then I'd just add a breakout board, lots of pins aren't used, it's in a DSO138 9V DC oscilloscope, I have 2. Quite useful for being isolated. Looks cool in the wooden frame/stand I made for it. And I also modded it to run it off a linear 12V transformer.

[Ian.M]

Hmm.  If you are using lots of extra flux and still getting bridging that doesn't clean up easily with desolder braid there must be something wrong.

Possibilities include:
Improperly tinned bit, maybe suffering from dewetting
Grossly excessive bit temperature
Low grade solder, with a high proportion of dross
Fake flux
Poor board quality with insufficient clearance or copper whiskers between pads.
Grossly contaminated desolder braid that doesn't wick easily

Where did you get your solder, flux and braid from, what brands are they supposed to be, and how old are they?
What is the make and model of your iron, what temperature is it set to, and is it calibrated?

Closeup photos of your board and bit may also help us diagnose why you are having major problems.

[anvoice]

There's expensive conductive epoxy out there that might be enough for some signals (not as good as solder connection), as well as dubious-quality conductive glue. It may be better though to get a new component at this point though.