Dead QFP44 packages available for SM soldering practice?
xanatos
Posts: 1,120
Bought my soon-to-be reflow oven today... have solder paste... ready to go! I'm wondering if Parallax or others may have a handful or two of dead QFP44 (such as propeller uses) that could be used to perfect one's SM soldering techniques? Since I anticipate that 75% of the SM projects I'll be making will use the propeller, I figured that would be a good thing to perfect 
Thanks!
Thanks!
Comments
Dave
http://www.intertronics.co.uk/products/cdummy.htm
I don't know what they cost, though.
It looked like they had some 44-pin dummies on page 54 of their catalog.
I had no idea there were chips which stacked on top of one another. Looking through their catalog was an educational experience.
I'll keep the board posted once I find out in case future folks want this same info.
Dave
Why don't you just order some "genuine" chips from Ebay? They're as good as any dummy chip and probably cheaper too!
You may have a very good point there... There's probably a bunch of Chinese-made knockoffs of something in a QFP44 package that I can get at 50 for a dollar!
I'll check & let everybody know...
OK, 50 pieces, $57.99, not too bad:
http://www.ebay.com/itm/50-PCS-AT89S52-24AU-AT89S52-QFP-44-8-bit-Microcontroller-/400576822198?pt=LH_DefaultDomain_0&hash=item5d443d3bb6
Dave
Frankly though, I feel that you don't really need to "practice" soldering QFP anyway. It really is quite simple and I just run a bead of paste across the 4 sides, drop the chip down, smudge it around to make sure it's seated properly, align it (which is now easier that it's smudged) and then drop it into the preheated toaster oven for 4 mins. I place my PCBs onto some folded foil that sits on the sliding tray. This helps prevent hotspots and also cushions the pcb from vibrations to an extent as well as help it cool off quicker. So after 4 mins on high I just pull the tray out and let it cool, maybe with a gentle fan (you don't want the thing to blow away). This works every time (and I have done thousands this way), don't overthink it, just try it.
I thought sm was harder than it is before also.
The key is to have a nice wet sponge ready, a really nice soldering gun with precision temp soldering gun like ones by the company PACE. "SODR TEK"
They sell tips for their guns also, and are some very nice long lasting tips with very precise tips.
With QFP, you will want to pre wet one pin in each opposite corner. Any two pins opposite corners.
So pin 1 and pin 23 would be two good pins to choose on the pcb to pre-solder with a bit of solder.
Oh, and getting small thin solder also makes this much easier.
Once you have your two pads with solder, place the qfp44 as close to its proper position as you can. it won'y stay because the two pads you soldered will get in its way.
With a tweezers, manipulate the prop chip so pin 1 is lined up with pin1 pad, solder it, if it gets off alignment, thats ok.
Now prepare to align the qfp44 to the other pin you already soldered, you will do this by getting the pin1 hot again so you can turn the prop into proper place,
You repeat this process untill the prop is very closely aligned but still only attached on pin1. you never tweak the angle of the qfp44 until you are sure pin1 is nice and hot and solder flowing. you can let off the pin1 heat and hold the part in proper place with the tweezers.
Once you have the qfp44 in place using only 1 pin soldered, you can then carefully solder pin 23 which is on the opposite side of the qfp44. Even if you solder both corners, you can still undo one of them and get the qfp44 re-adjusted.
The hard part is seeing what you are doing. A usb webcam(or a cam made for working with small parts(adafruit.com sells one) and a nice bright light
The FTDI FT230X datasheet has a nice graph under 9.5 Solder Reflow Profile
Here is the table (UNLEADED SOLDER PASTE) I have worked out to solder my boards (note the temp probe maxes out at 200C) (Didn't record the actual values from the ovens probe)
If you look closely, you will find some shorts. These photos were taken before I realised that the pcbs near the outside of the oven drawer were not reaching temp. By only doing 3 pcbs at a time, or increasing the time at 260C another 10 secs, would fix this.
I have a Torch T200C+ oven.
Actually it is even easier than that although solder paste and the oven is the easiest.
A long time ago I would solder QFPs with a soldering iron, just your normal temp controlled iron, nothing special except a good tip. Instead of a very fine tip you are better off with a clean chisel tip and after tacking the corners and making sure the chip is seated properly against the pcb (important) I would just turn down the iron a bit then blob solder all down the pins in one great big mess. Since the iron was a bit cooler it didn't burn off all the flux so you can turn up the iron nice and hot and holding the pcb at a bit of a shallow angle run the tip down each side letting the solder follow the tip until you get to flick it all off after the end pin on each side. Once you have seen it done or done it yourself you start to realize that things are far easier and quicker when you stop trying to be overly precise. Leave the fine tips in the drawer, they are too fiddly and don't conduct enough heat to the pad anyway, let the flux do the work. If you do happen to have a solder bridge then try squeezing some flux onto it first and letting the hot tip do the work of making it reflow away.
Best solution though is fresh solder paste and a toaster oven plus flux if needed. I have a little 12V/mains combo cooler that I keep my paste and glues in etc so they are always as fresh as can be. The solder paste I buy in syringes but I normally load them into a manual dispensing gun as it is much easier.
EDIT: Come to think of it I use 2 trays in my oven and I leave the bottom tray in place and use the middle shelf for the pcb tray while using folded layers of foil to rest the pcbs on. The reason I say this is because I decided to do a quick IR temperature measurement of a pcb which I placed directly onto the bottom tray. After a few minutes I had volumes of smoke coming out of the oven which I had to quickly extinguish while the phones rang etc. It's just too hot like that of course.