Anyone ever work with TDFN/TQFN chips before? - Page 1
Forum section: electronics / general

author: TopherTheME
author_rank: Regular Contributor
timestamp: September 08, 2010, 09:00:35 pm
content: I'm in the (extremely) painful process of designing some instrumentation for some research at school and a lot of the chips I plan to use only come in no-pin packages like DFN and QFN. I've never soldered one of these chips before and wondering if they are easy to destroy if hand soldered. I can hand solder just about all type QFP packaged chips with just a $15 soldering iron but I don't think thats going to cut it for these. I have access to a OK hot air station but only used it for basic SMD stuff that has pins. I've also got access to a lab grade oven that will hit 250C. Do you think this is doable?

author: Unknown
author_rank: Unknown
timestamp: September 08, 2010, 09:10:22 pm
content: I think there might been some tutorials around on sites like Sparkfun. No experience myself, I hate probing these things (nothing to clip on to), let alone soldering them. But I believe it's possible. The only worse package for hobbyists is BGA in my opinion. Reflow soldering (hot air or oven) would probably be my first attempt, although it may be possible with a soldering iron and a package with pins extending all the way to the edge (or extra long pads). Don't be surprised if it takes several attempts to get it right.

author: scrat
author_rank: Frequent Contributor
timestamp: September 08, 2010, 09:41:48 pm
content: As long as there are a sort of lateral leads, it is possible to solder them manually...I'm not a very experienced solderer, but once I soldered one of thesehttp://focus.ti.com/lit/ds/symlink/tps61200.pdf(go to the last pages). They have 0.5mm pitch, and the board had no solder resist.I used a soldering station with a very thin iron, which costed a lot. However, I don't think it would be impossible to solder it with a cheaper iron.You surely need flux fluid and solder wick. If the board is not pre-soldered, just cover the pads with solder (with the wick you can leave only a very thin layer), then solder down the usual opposite (diagonal) pins, adjusting rotation.It gets easier if the tracks which arrive to the pads are quite long (more than some mm): you can easily add or remove tin by going back or forth on the track.Good luck!

author: cksa
author_rank: Regular Contributor
timestamp: September 08, 2010, 10:08:58 pm
content: Very easy with a hot air rework station. Just did a few LGA packages the other dayIf they're QFN or DFN's with connected sides and no need to solder the bottom pad --> a soldering iron and some flux works well.If you do need to solder the bottom pad, either go the hot air route, the reflow skillet (as seen on various hobby sites), or just make a large hole at the centre of your part footprint, and just stick your soldering iron/solder through there when you are assembling it. Only for prototyping though.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 08, 2010, 10:17:39 pm
content: Yes - just did a run of boards with a total of about 500 QFN24s with 0.5mm pitch.The number one tip is to make sure the pads are sized such that there is 0.5 to 1mm of pad extending outside the package outline.I had a lot of problems with solder shorts, due to the solder paste stencil apertures being too big, but having the extended pads made it easy to rework most of them by just appluing flix and wiping an iron along the side to mop up the excess.The number two tip is to put a large cutout in the solder resist on the underside. This allows an iron to get good thermal coupling through the vias the the bottom die pad for reflow, where required. I find that heating by direct contact (add a little solder) with the underside is more effective than hot air, as the latter tends to heat a wide area, causing other surrounding parts to potentially get blown off.Tip number three is to not put other parts too close to the package, to allow working room for inspection and rework.To hand-solder, I've used 2 methods:1) solder paste on the pads (stencil or manual dispense), place part, then heat using iron as above. Unless you can stencil it, this is not an especially good method.2) apply flux and then put solder on all the pads - a wipe across with a large tip whiile applying solder works well, or you can splodge some paste on and reflow it. When you have nice beads of solder on the pads, clean the old flux off and apply fresh flux. Make sure there isn't much solder on the centre pad - I'd suggest not putting any on, just a small blob of paste.Clamp the PCB in a vice in such a way that you can apply an iron to the bottom pad while working on the topApply flux to the bottom of the part, place it with tweezers. Precise placement isn't too important at this stage.Apply the iron to the underside pad, and once it heats though, if necessary use tweezers to prod the chip into place - as soon as the pads are aligned, you will see it 'jump' into place - if initial placement is close enough it will do thos with no further prodding.While the solder is still molten, gently tap the chip down - it will bounce up again due to the solder surface tension, but doing this helps avoid any voids where there was less solder on some pads, and also shake out any shorts.And as always don't even think about doing this with leadfree solder!You will need a decent iron that can pump plenty of heat in without overshooting - ideally a Metcal.

author: scrat
author_rank: Frequent Contributor
timestamp: September 08, 2010, 11:11:30 pm
content: Quote from: mikeselectricstuff on September 08, 2010, 10:17:39 pmWhen I used a high end set for hot air rework, some small protective metal screens were included. They prevent from heating other parts surrounding the one under work. I think they can be easily replaced by homemade ones (aluminium or steel boxes without top nor bottom). They are in the stand at the bottom-centre of the picture:http://www.jbctools.com/advanced-series/stations/desoldering-rework/234-desoldering-rework/385-am-rework-station

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 08, 2010, 11:42:18 pm
content: I just did a

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 08, 2010, 11:51:18 pm
content: QuoteIf the oven has a reasonable rate-of-rise (a few degrees per sec) without getting too windy if it's a convection one, and has a window to see what's going on, and you use leaded paste it should be ok, otherwise go buy a cheap toaster oven. Give it a dry run on a scrap board first...For a build of a new board, the best and easiest way would be to do it 'properly' - stencil paste on (polyester stencil -$10-15, although for QFNs it's worth splashing out on a stainless one, maybe $100-150), hand-place carefuly and toast it. Don't worry too much about trying to match reflow profiles - a ramp rate that starts melting the solder after 90-120 secs works fine.From experience I'd say you want to shrink the QFN pad sizes on the stencil - maybe 50-75% of the area of the pad, and probably use 4 small holes for the large centre pad.

author: TopherTheME
author_rank: Regular Contributor
timestamp: September 09, 2010, 03:16:49 am
content: Thanks for all the replies. I think I'm going to give the iron and hot air gun a shot and see which works best. The oven I have has a ramp rate of about 10'C/min so its probably not fast enough. I don't think my iron is going to cut it for stuff like this either but I'll give it a go with my uni's community metcal irons.

author: djsb
author_rank: Super Contributor
timestamp: September 09, 2010, 08:31:25 am
content: Is that centre square pad in the video plated through in some way (are the holes plated through via's?)? How would that be specified when sending a design to a board house?David.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 09, 2010, 09:11:55 am
content: Quote from: djsb on September 09, 2010, 08:31:25 amYes - there are a bunch of PTH vias within the pad. These help with heat transfer to a goroundplane for power parts, and reduce inductance for RF parts. For run-of-the-mill parts without cooling issues they aren't strictly necessary, however they help draw excess solder away - without them, there is no path for excess solder or flux from the centre pad to escape, and this can lift the part off the board slightly, causing voids on the peripheral pads.Depends on your PCB software how you actually do it, some parts libraries may already have vias, if not you just stick a bunch of vias down on top of the pad and connect them to the centre pad's net to avoid DRC errors.

author: TopherTheME
author_rank: Regular Contributor
timestamp: October 07, 2010, 04:30:24 am
content: I did it!I soldered my first QFN chip today. It was a lot easier than I thought it was. I just tinned the pads, added a little flux, plopped the chip on, then added some heat from my new hot air station. The chip just sort of "popped" into place and it was ready to go.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 07, 2010, 07:40:39 am
content: congrats mechy! what chip is it?

author: TheDirty
author_rank: Frequent Contributor
timestamp: October 07, 2010, 12:01:55 pm
content: Good work. Ya, QFN's seem like they would be difficult, but it's not that hard at all with hot air. They are also manageable with an iron if enough of the PCB footprint extends from below the chip.

author: TopherTheME
author_rank: Regular Contributor
timestamp: October 07, 2010, 02:10:59 pm
content: Quote from: shafri on October 07, 2010, 07:40:39 amIts a Maxim MAX1932QuoteThat was going to be plan B.

author: DJPhil
author_rank: Frequent Contributor
timestamp: October 07, 2010, 10:59:14 pm
content: Excellent work on that, very nice!As much of a pain as they are, I really like the no-lead chips. They just look so neat and clean when everything's finished.Quote from: TopherTheME on October 07, 2010, 02:10:59 pmNow I'm curious, what's the application? Fiber transceiver? Laser rangefinder?

author: TopherTheME
author_rank: Regular Contributor
timestamp: October 08, 2010, 02:27:17 am
content: I'm starting to take a shine to them as well. They do add a bit of "cool factor" to a board.QuoteWell...its complicated but it basically for very sensitive light detection for measuring temperature.

author: Time
author_rank: Frequent Contributor
timestamp: October 08, 2010, 02:29:30 pm
content: Quote from: TopherTheME on October 07, 2010, 04:30:24 amYep, I prefer a hot air station for all my SMD soldering needs. I can use minimal paste and the joints look way more professional. It makes everything a breeze.