Seemingly Impossible - BUT HEY!!! They seem to do it...

[Clyd3]

Hi,
I need to be able to solder those really difficult ICs, with like 80 tiny pins, which are really small and really close together...
I think its called a TQFP package or something.
Do I need really special equipment?
Do you think it would be better for me to rather solder a socket in place than the IC itself.
its a dsPIC...

 

[Styx]

braver man then me trying to solder them.

I have heard the technique of using alot of solder-FLUX and lying a strip of fine solder along all the pins on one side (ie shorting them out), then running the soldering iron along them - the flux will tend to pull the solder onto the pins to stop bridging.

 

[Clyd3]

that seems like a good idea, I'll try it, thanks Styx...
Anybody else???

 

[heathtech]

I don't have a comment other than THAT is a really disturbing picture.

 

[Clyd3]

yeah, its a bit distracting <which I like - dont know about you>, but I need to make it a little shorter...
cant seem to access the server right now though...

 

[mstechca]

Those devices are SMT devices (surface mount technology).

and shrink that picture of that guy (Is it Jackie chan?), and make it your avatar

 

[ThermalRunaway]

I've succesfully removed and refitted SMD microprocessors with over 200 tiny pins, it's all about patience, and practice. Regarding tools all you really need is a decent soldering iron (prefferably temperature controlled), a stand with a wet sponge to keep the tip clean with, some thin solder, a tube of liquid flux, and some appropriate flux-cleaner to wash off the residue afterwards.

For technique I tend to start by accurately lining the IC up onto the PCB pads and then, once I'm certain that the IC is properly aligned onto the land points and is of the correct orientation, I tack each corner down with a blob of solder. I don't worry myself with being neat at this point - as long as the IC is securely tacked down so that it's not going to move from it's perfectly aligned position, I'm happy.

Once the IC is tacked down in place, it's a good idea to double-check yourself that you've fitted it with the correct orientation. You might think you're already certain of this but believe me there's nothing more frustrating than painstakingly soldering in an IC with like 200-pins, sitting down with a cuppa to admire the neatness of your work and then realising with absolute HORROR that you've fitted it the wrong way around and that it's all got to come back off. Double check yourself.

Once you're sure, it's time to get the flux out. I tend to tackle ICs like this one side at a time by laying a slither of solder horizontally across the edges of the pins so that it covers the points where the pins meet the PCB solder points. If you haven't had much practise soldering these types of ICs it's then best to solder each pin one at a time, making sure to use only a little solder at a time and to clean the tip off regularly. If you're confident, it's a lot quicker to gather a small resevoir of solder onto the tip of your iron (you need an angled point for this) and then run the iron down the board at the points where the pins meet the PCB tracks. As long as you're careful not to bend any pins and you're not so rough that there's any risk of damaging the PCB tracks, the solder will flow neatly over all of the pins with the flux taking care of the rest. If you're good at this technique you can finish with some VERY neat results - the guys in work tell me that it's difficult to tell the difference between my finishes and that of a professionaly soldered board other than the fact the solder looks fresh! Sometimes you'll find that the odd couple of pins will get grouped together with solder - just go back and take care of these later.

Once you've done the entire IC, make sure to go back and check each pin individually to make sure it's actually been soldered. It may look like it is, but the only way to tell if it's taken to the board is to aggrevate each individual pin with a sharp tool (I use a dentist-type hook). A good bench magnifier is a good tool to have at this point (infact it's useful during the entire procedeure). I use a Luxo bench magnifiying lamp.

Once you're happy, and assuming you haven't realised with HORROR that you've fitted the IC the wrong way around, clean off the board with your flux cleaner.

Brian

 

[upand_at_them]

The technique is called "drag soldering". Watch the 3rd video on this page:

**broken link removed**

Mike

 

[Clyd3]

thanks a lot Thermalrunnaway, that's really useful... gonna do exactly what you said... thanks

 

[Clyd3]

i'll fix the avatar / sig in the morning, 'cause the size limit 4 avatar is too small...
nice vid...
goodnight...
<says thanks again in his sleep:zzzzz>

 

[Halogrunt1234]

a technique that I have learned in class was to use solder paste that has been applied straight across the pins, then use one of those hot air blowers to melt the solder paste. when it melts, the wonderful property of solder to only bond with metal will separate the line of paste onto each little pin and will effectively solder each and every one of them. the only problem would be that if you use the hot air blower for too long or point it directly at the IC package, you will damage the IC.

I have had no experience at doing this though, I only saw it on a video shown t the class.

BUT I DID STAY AT A HOLIDAY INN EXPRESS

 

[Exo]

see that the pads on the pcb are tinned first,
to do this just solder them, it doesnt matter if they all stick together
Then use solder wich to clean it all up, you'll end up with nice and flat tinned pads (maybe you should practice this on a dummy board first before doing your good pcb)


Then tin the pins on the chip, lie it down on a hard surface that can stand soldering temperatures and solder the tips of the ic's pins, again if they stick together use the wick...

now put flux on the pcb pads and place the chip, and just run your soldering iron across the pins... The solder should stick to the pins, not connecting any of em together, but you can again use the wick should there be some pins soldered together...

it's real simple and fun once you get the hang of it
you can order dummy ic's to practive (empty ic packages, they look like an ic but there's no chip inside, making them very cheap and good to train)

 

[ThermalRunaway]

I don't like solder paste. I tried it and found that the stuff just gets everywhere - excess paste flows inbetween and underneath the pins, and I found that I could never quite get it clean afterwards.

Anyone else a fan of solder paste?

Brian

 

[Nigel Goodwin]

I don't like solder paste. I tried it and found that the stuff just gets everywhere - excess paste flows inbetween and underneath the pins, and I found that I could never quite get it clean afterwards.

Anyone else a fan of solder paste?

Not me! - I'm a fan of liquid flux - as for Exo's method, there should be no need to tin the chip pins, they are already tinned!.

 

[Exo]

it seems to work better for me with some extra tinning, but you could always try without first...

 

[ThermalRunaway]

I find that if you tin the pads you end up with differing thicknesses of surface due to human inaccuracies when applying the solder. The consequence of this is that not all of the IC pins fall flush with the pads and therefore not all of them take properly when you're reflowing it.

We all have our own preferences though I suppose.

Brian

 

[Clyd3]

yeah, that's true, but to find our preferences we have to do many different types, or at least something, so that's what I'll do.
Will prove interesting...