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Forum Index : Microcontroller and PC projects : I give up on qfp
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| kkoppert Newbie  Joined: 12/04/2017 Location: New ZealandPosts: 17 |
OK I know this is off topic but I'm severely depressed, I can't solder 44, 64 or 100 tqfp packages to circuit board. I think the score is 1 44 pin and possibly one 64 pin successes out of 3 44 pin and 2 64 pin. My hands aren't super steady and my eyesight isn't eagle eye, which don't help, but with patience and lots of foul language I can usually position and tack the chip without destroying it (at least on 44 and 64 pin stuff) but when it comes to soldering the other pins I can't get the technique right. I have tried soldering the pins one by one (results in bridging) and flood soldering (results in more bridging). Contrary to all I can find on the internet I find removing the bridges using solder-wick, solder sucker nigh on impossible and the chip get destroyed or the board gets destroyed. The latest effort, a 44 pin pic32mx270 has a chip taken out above pin 6 and still has bridging (this using low temperature solder and lower temperature on the iron). Please, please can someone suggest a method of avoiding or safely removing bridges. |
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9082 |
Hello.  Sorry to hear of your SMD pain.  Lets see if we can help you with that.There is no one method that is best. Generally speaking, it is just whatever works for the person concerned. Do you have a microscope? You really do have to have one for SMD work - especially once you get down to the 0.5mm pin pitch stuff. A magnifying headset will normally only give you 2x or 3x magnification. You need about 10x for small SMD stuff, and when finished, I then blow that up to 30x so you can examine if you have any bridges etc. Anyhoo... BRIDGING - Even if your hands are not so steady, it is still possible to solder SMD with the right technique. I speak from experience as someone who for years would not touch and SMD - not even SOIC stuff - as I was too scared to solder them. To get around the bridging problem, you have to reduce the amount of solder you are applying to the iron tip. You will perhaps be surprised by how many pins you can solder with only a tiny amount of solder on the tip. If you are soldering 0.5mm pitch, you apply a tiny amount of solder to the iron tip. If you can see a blob of solder on the iron, you have way too much solder, and it will bridge like mad. Generally speaking, if you are 'Drag soldering' by running the iron down the pins in one or more strokes, if you have the right amount of solder on the tip, the solder blob will follow the iron, soldering all the pins as you go, but it WON'T bridge out the pins - this is the magic surface-tension of the solder in that it only sticks to what it wants to, provided you don't have too much solder on the iron. If in doubt, wipe the tip clean, and apply new solder. What type and size of solder are you using? 1mm is WAY too thick, and even 0.71mm is too thick for QFP's IMHO. I use 0.5mm 60/40 solder. I have plenty of this, so if you would like some, PM me and I can send you some for free as a roll of 0.5mm solder of decent quality will cost you about $50 and you most likely don't want a whole roll of the stuff.... I also recommend SMD practise kits from the likes of eBay or Aliexpress if you are new to SMD - practise on those, where it does not matter if you lift pads on the PCB etc, cos the entire kit with some old SMD chips is only about five bucks. You MUST use flux. I prefex gel flux, but liquid is also OK. MUST be electronic flux, not the acidic flux from the garage for soldering copper spouting together!  If you are really stuck, I am happy to help by soldering whatever chips you need done - flick me a PM. Smoke makes things work. When the smoke gets out, it stops! |
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| robert.rozee Guru  Joined: 31/12/2012 Location: New ZealandPosts: 2294 |
you actually want a reasonably hot iron, temperature controlled and set to 370 degrees or more. you also need LOTS of flux; do NOT rely upon just the flux within the solder. i use a flux paste called SP-44 from kester, though i am not sure it is still being manufactured. some folks swear by liquid flux pens, i've always found them pretty useless and swear by flux paste myself. and DO NOT use lead-free solder, it is far more difficult to use. use good ol' 60/40 or 63/37 solder. that is 60% (or 63%) tin. be wary of 40/60 solder in unmarked packets, and NEVER buy cheap chinese solder as it is invariably unusable. with lots of flux and a hot iron, solder wick works well on the solder bridges that EVERYONE experiences with SMD parts. i'd keep well away from any sort od solder sucker. where abouts in nz are you? there may be a forum member in the same city who can lend a hand. cheers, rob :-) |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9082 |
[Quote=Rob]you also need LOTS of flux; do NOT rely upon just the flux within the solder.[/Quote] So true. Flux-cored solder is fine for doing through-hole or tinning wires etc, but don't expect the flux in the solder to help you with SMD, as the flux in the solder itself burns off a few seconds after you apply it to the iron tip. DON'T GIVE UP AND DON'T LOSE HOPE!  All of us who can solder SMD now, had to learn how to do it, and we ALL made mistakes and some solder bridging is pretty much fair game with SMD soldering.  You do try to minimize that though, but it happens to the best of us. I find that when you get a bridge, provided it is only over two or three pins, apply flux to the bridge, then just heat it with a clean iron tip, pulling the iron straight away from the pins. The flux will help the solder bridge melt and move to the hot iron, and in the process, this clears the bridge. Only works if with small bridges. If you have big bridges with lots of solder, you do need to wick it away first. Use decent quality wick, and as Rob says - don't buy the cheap Chinese rubbish. I use Goot Wick from Jaycar. It is about $7 for a small roll, but it works so well, I would never get anything else. Smoke makes things work. When the smoke gets out, it stops! |
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| WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2794 |
After literally soldering hundreds of SMD MicroMite modules (and often with compliments on the standard of soldering  ) I can offer the following advice & tips.First of all, don't give up. The effort spent learning will benefit you well. EQUIPMENT: You do not nee any expensive kit for SMD soldering. I use an ordinary 18w (230v) Antex iron. This is not a temp controlled iron - just a normal 'fixed temp' iron. If possible, get one with a silicone lead as these are much more flexible and make the iron feel more 'controllable' in terms of movement. On the iron I use a chisel bit 1.6mm works well for me - the flat part allows a nice surface area for heat transfer. I would avoid a pointed tip at all cost! Use leaded solder (if I'm allowed to say that!). Much better to work with than the 'green' unleaded stuff. I use 60/40 Tin/Lead at 0.7mm diameter. This covers all SMD sizes/pitches, and 'normal' through-hole components too. Magnifier of some description will be required. I have a low cost illuminated one on a telescopic type arm. Gives 10x mag. The most important thing for SMD work is a liquid Flux pen (refillable is better for obvious reasons), and solder wick. I use 1.5mm wick. If you use much thicker wick, then the heat transfer is worse with an 18W iron. Any thinner wick will be used up too quick. Also a pair of metal tweezers for picking up and placing components. TECHNIQUE: Locating & Initial fix: I always apply a blob of solder to one PCB pad first for any SMD component. Then holding the component with the tweezers, I heat the blob, and position the component. When in place the iron is removed and component held in place for a few seconds to allow solder to cool down. Check the component is lying flat against the PCB, and 'lined up' ok. If not, the simply reheat the blob and re-position. This technique works for all SMD components resulting in a lined up component ready for soldering all the other pads/legs. For TQFPs, I use my finger to position the component rather than the tweezers. Solder remaining pads: Now for two-pad SMD components 0805/1206/1210, simply solder the second pad once you are happy with alignment. For TQFP I literally flood a row of pins with liquid flux, and then apply solder to the iron, and then run the iron over the 'flooded' pins. DO NOT WORRY ABOUT ANY BRIDGING AT THIS TIME. Clean Up: Apply liquid flus to wick, ensure no solder on iron tip, and touch wick to pad/pins and then touch the flat part of the chisel tip to the wick. The solder will magically absorb into the wick leaving a nice clean joint. The thing to master here is how long to leave the iron on for. Too long and you will remove too much solder. Too little time, and the joint will look messy. Be sure to remove the wick with the iron (i.e. remove both at the same time). If you remove the iron first, and then pull away the wick, the solder may have already 'hardened' and you may damage pins/tracks when 'forcing' off the wick. Simply apply the iron to the wick should it get 'stuck' For TQFPs, lay the 'wet wick' across the pins rather than 'poking it end-on at the pins'. This can then be dragged along the row of pins once you have mastered the technique. As mentioned by other above, soldering is a personal thing and what works well for one person may not work as well for another. However, there are some common things amongst the different techniques. These are, Hot iron, flux, magnification, and light. Along with the above replies, I hope this will 'encourage' you to keep trying. WW For everything Micromite visit micromite.org Direct Email: whitewizzard@micromite.o |
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| Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814 |
Ive soldered literally millions of smd joints at a previous job (electronics pcb assembly for mining equipment) and it isnt that hard once you know the tricks I used superglue (apply with pin) to hold the component in place )note it does smell when it gets hot, but I had an industrial fume extractor to play under, a couple of large computer fans sucking away from you will work in a well ventilated room) I had several bits to choose from, a `large' chisel about 5mm is good to do several at once on a temp controlled iron, and (not always available in all brands) a .1mm needle tip (industrial weller) - that was literally a needle, it would draw blood! Always preflux, I prefer paste fluxs myself, others liquid- in either case it MUST be for soldering electronics not plumbers paste!!!!- I apply with a pin to each pin individually, others just wiped it across multiple pins Viewing- you absolutely need a magnifier- I tend to steer away from the megalarge single illuminated ones (we had one with a fluro)) it lit the area well but I had trouble with depth perception with it- I found the binocular headsets with the flipdown lenses much better, and a binocular microscope the best, but tiring to work with for hours on end (hint at least once every 15 min, look away at something distant to reduce eye strain) (I'm `lucky' in that I am extremely shortsighted and can actually focus down to wthin a cm of my eyeball- so I often used to just `naked eyeball' joints with no magnification just up really close- I have actually burnt my nose with a soldering iron tip soldering a particularly difficult joint with tiny coils etc that were really difficult to see with the microscope when soldering lol) Use LOTS of light- I used to use 2 60w flexi desklamps back in the day(not pleasant in hot weather), but led desklamps are the ducknuts as far as I am concerned, one each side of the bench Have a tool tray with needles, tweezers (pointy and flat) solder wick (prefluxed but I always ended up adding more flux to the end myself) If you have `shakey hands' (and I often did on a monday lol) use wrist braces to help- I used to buy a pair of mousepads that had those silicon wrist supports on them, perfect and very comfy, leave your wrists on those and use your fingertips for control (I never could use chopsticks until I started soldering smd's- now I can actually hold two wires on one hand and actually maneuver them around until they touch, using two fingers each on the one hand- looks kinda like the vulcan salute from startrek only with a piece of wire inbetween each group of fingers lol Soldering- I usually used the chisel to do the `wipe the pins and slide away' technique, after a bit of practice, you rarely needed to go back for bridging repairs- if you did get a stubborn bridge, let it cool down, then dab your solderwick into some flux and turn up the iron a bit more (I ran at 350-370 normally, up to 400 when using the wick and suck up the excess (forget suckers, they just dont work that well on smd imho) then retry, for really stubborn ones I'd swap over the tip to the needletip and redo each leg individually (normally misplaced or missing mask on the pcb) I kept a pair of small needlenose pliers to hand to swap over the tips hot, and just drop the hot tip in the sponge Wow!!- sorry about the length of this- another `mininovel' post  |
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MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
For removing a bride i clean the tip and put a tiny bit of solder on it. Then flux on the pins that are bridged. Then hold the tip against the side of the pins. Solder likes to flow TO the heat so it pulls most of it on the tip. You then remove the tip away and most of the solder will be drawn away with the tip. This need to be done fast as the little pins heat up quickly and then it does not work. This will get rid of a solder blob, often a tiny bridge still remains. Use solder wick and lots of flux and make sure the tip is large and hot enough (350+). As the tip is hot do not leave it to long as it will overheat the chip. If you have lots of bridges, take your time and let it cool down before working on the next. Another way of soldering is to first tin the pad, use flux so the pads are clean and are covered completely with a thin even layer of solder. If not even, go over it again until it is, you have a little bit of margin. Then place the chip and tack two opposite pins to prevent it from moving. Clean the tip, add flux to the pins, add some solder to the tip and touch the pins from the side one by one. With a wide tip you can do it by turning it 90 degrees so the short part is touching it. The solder on the tip and the solder that is already on the pad will flow and if you do it right with practice you will solder a single pin. Don't solder the pins in sequence but skip two pins. This will keep the pins in between relatively cold and solder bridges are prevented. Microblocks. Build with logic. |
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| WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2794 |
For everything Micromite visit micromite.org Direct Email: whitewizzard@micromite.o |
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CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 1995 |
you bad lad |
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| kkoppert Newbie Joined: 12/04/2017 Location: New ZealandPosts: 17 |
Thanks everyone for all your useful information. I guess my problem is lack of practice, what I need is a barrel full of dud chips and faulty PCBs and possibly a better microscope. I use a Hakko clone soldering iron (with a hotair gun) a 3mm chisel tip and a pointy tip. 0.3mm and 0.7mm 63/37 solder. Temperature is not that accurate but I have a Hakko tip temperature thermometer. I've started using heaps of rosin in IPA flux unfortunately this seems to leave a charred gummy residue. The wick I use is el cheapo aliexpess stuff so I've ordered some chemtronics? soder-wick |
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| Andrew_G Guru Joined: 18/10/2016 Location: AustraliaPosts: 842 |
Hi, its encouraging that there are so many TBS people happy to help. I particularly like the suggestion to skip a few pins to reduce the likelihood of bridging. Here is a similar topic I started a few days ago with some useful input too. (My Microscope might arrive on Monday?? - less than a week from the US (OK is was about $Au90 for DHL)). Cheers, Andrew |
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Quazee137 Guru Joined: 07/08/2016 Location: United StatesPosts: 529 |
I too have avoided this. Awhile back I reworked a board that had what seemed like a thicker silk screen between the pins giving me a channel for the pins made it easy to do. Now wondering if it can be done in Eagle and other PCB programs. It may help with the bridging. Something like schmartboard.com has the pins in a slot. I have used two of their boards in the past for proof of concept designs that had to get done fast. Here is a link for those that need a quick and easy way to use use 32 to 100 pin QFP 5mm pitch. http://schmartboard.com/schmartboard-ez-qfp-32-100-pins-0-5mm-pitch-2-x-2-grid-202-0011-01/ this one is only $10 USD. |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9082 |
Indeed!!!!! Back on topic, I really DO speak from my own terror of soldering SMD. For YEARS I would not touch the stuff. More then a few times, I would avoid a project in Silicon Chip or Electronics Australia(when it was around) if they used even SOIC or one or two SOT23 transistors. Now I can just about do them with my eyes closed. The tiny 0.5mm pin-pitch stuff I was also terrified of for years, but they are REMARKABLY easy to solder by hand, once you have the right equipment. WW has already laid all that down in his post, but yes, I considder at a MINIMUM, to work on SMD soldering from 0.5mm pitch up, you need to have: - 0.5mm 60/40 lead solder. You can use 0.7, but it is easy to put too much on the iron with 0.7mm. 0.5mm just gives you that little bit more control in how much solder you apply to your iron tip. - Microscope with 10x eyepiece lens, and 1x/3x objective lens, so you can do the work at 10x, and check the finished result at 30x. Headset magnifying things just won't cut it for the 0.5mm stuff - they don't blow up the image big enough for you to clearly see what you are trying to do. - Flux and solder wick. ...but I think I am now repeating myself and/or paraphrasing others, so I will stop now!  Smoke makes things work. When the smoke gets out, it stops! |
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