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Using Arduino => General Electronics => Topic started by: bilbo on Aug 26, 2011, 06:55 am

Title: TQFP Soldering
Post by: bilbo on Aug 26, 2011, 06:55 am
Hi all,
There is a project I had in mind using the At90USB1287, which is a TQFP 64 package. I know that there are breakout boards available, but I am trying to save money, plus I would much rather fab it from scratch. I have a lot of experience through hole soldering, and have done a good amount of SOT and SOIC soldering, but no QFP. I have seen a bunch of different methods on youtube and the interwebs, and I was wondering what those of you with more SMD experience think is the best.

Thanks!
Title: Re: TQFP Soldering
Post by: ilektron on Aug 26, 2011, 04:18 pm
I do a lot of lqfp soldering by hand.  The key?  Having some sort of microscope or magnifying glass.  I usually try to tack it in place with one pin while holding it in place.  Then, you can still wiggle the piece to align it a little more, and tack down the other side.

I usually try to hit each pin individually with a soldering iron, but usually I end up running the soldering iron with a little solder on it across the pins.  You will need some flux and definitely some solder wick to clean up any excess solder.  Also, a good soldering iron with a clean tip helps a lot.

Good luck!  It looks harder than it is!
Title: Re: TQFP Soldering
Post by: cmiyc on Aug 26, 2011, 04:29 pm
Quote
I was wondering what those of you with more SMD experience think is the best.

"Best" is a strange term.  Best for one person won't be best for someone else.

I generally follow the same method as ilektron. 

I have found with good quality solder wick and lots of flux the method of "flooding" the pins with solder, and then "sucking up" what is left does actually work well.  However it takes practice.  The practice came from trying to solder one pin at a time and messing up along the way.

In addition to some form of magnification, you'll want some good light.
Title: Re: TQFP Soldering
Post by: pwillard on Aug 26, 2011, 04:48 pm
lots and lots of flux...

I use a water soluble spray flux
Title: Re: TQFP Soldering
Post by: MarkT on Aug 28, 2011, 11:47 am
The technique I've found most reliable (not necessarily the tidiest) is to pre-tin all the pads so they have a little ridge of solder on each (and flux aplenty).  Check no bridges between the pads.

You then tack-solder a couple of leads to get the device in place, then tack solder the rest using an absolute minimum of solder on the iron (freshly tinned but wiped).  The point is that the solder already on the pads reflows onto the leads with minimum risk of bridges forming.  Inspect with a lens to ensure every lead has bonded to its pad.  I've often had problems removing excess solder and bridges so its good not to risk this.  Also you can tack-solder several leads at a time by placing the iron's tip across them, which is fairly quick - you usually feel the leads sag down as the solder melts so you can tell its worked (apply a steady downwards pressure).

The downside is that the chips always a little high off the board as it started off resting on top of the ridges - its also tricky to position the chip as it keeps wanting to sit between the ridges and the first couple of tack-soldered joints require a steady hand (or three!).
Title: Re: TQFP Soldering
Post by: ilektron on Aug 28, 2011, 04:55 pm
I've tried the pre-tinning the pads, and that doesn't work for me.  I can never get it in place.

I use a blunt tip @ 660, no-clean flux, and the thinnest solder I can find.
Title: Re: TQFP Soldering
Post by: foxbat on Aug 28, 2011, 08:10 pm
I use the pre-tinning method then I weight down the IC slightly then reflow the solder with a hot air gun - an Aoyue 852A+ in my case. Afterwards I inspect and touch up with my finest tip iron working under a 20x binocular microscope. 100% success rate so far.