Soldering LFPQ64 - first time in a while. - Page 1
Forum section: electronics / beginners

author: paulca
author_rank: Super Contributor
timestamp: November 16, 2022, 06:17:50 pm
content: A lesson learnt.If you are buying a nice MCU chip for your project, don't just buy two in case you screw up the soldering... go find something else that is cheap as chips (pun) in the same package and have a few practice runs. Those green PCB DIN / Breadboard adapter boards are great, as they are a B*TCH.That was my lesson. I bought 2xSTM32F411REs, £17 each including VAT. I figured I'd wait until I had the board and stensil... what could possibly go wrong.With the PCB weeks out, I decided to solder one of them an adapter board. Well, 1 hour later if that STM32 survived that I'll be impressed.Lessons:LFPQ64 is quite tricky, it's not just 4 sides you have to line up and trying to shift it even 0.25mm while it's partly soldered, will bend pins. Also those adapter boards with the really, really, long pads, DO NOT ADD ANY SOLDER. At first those long pads soak away your heat, so you have to drag solder really slowly... when it starts to melt the pad tinning solder and it flows up into the pins bridging every last one of them.After the first side was a 100% bridge I knew it wasn't going to go well. I carried on with the other 3 sides, but on microscope inspection I had bridges everywere and the chip was out of line on one set of pins by about... too much!I ended up trying to remove the excess with solder braid, that didn't work well enough, so I hot air desoldered the ship. Cleaned it up, straighten some pins with the point of an exacto and started again on a new adapter. This time I did not use ANY solder, just the tinning on the pads and brought the iron is along the pad, not from above and watched the excess pad solder wick up the pin. Perfect. Still managed to get a few bridges.Inspecting with a microscope and it's had to tell, there are a few dubious pins and some I can't tell if they have a bridge behind them of it's just flux gunk I didn't get out with the alcohol.I suppose I will just to solder a few pin headers on and see if it will boot and draws the right amount of power.So, yes, I am ordering the cheapest bit of trash LPFQ64 chips off ebay and will practice before killing another valiant MCU!

author: rstofer
author_rank: Super Contributor
timestamp: November 16, 2022, 06:37:23 pm
content: As to bridges, I have had success running a bead of flux along a row of pins, laying in some SolderWick and just drawing solder out of the joint until the bridge is gone. Flux is the key to drag soldering.Solder a couple of corners first just to position the device. Get it perfect before proceeding.I have never used a stencil, I just dab solder paste on the pads. I prefer drag soldering.For things like capacitors, I put a dab of solder paste on both pads, position the device and hold it down with curved tweezers and touch the pad with the soldering tip.https://www.sparkfun.com/search/results?term=tweezerI actually prefer oven soldering even though I have to dab the paste on the pads.

author: paulca
author_rank: Super Contributor
timestamp: November 16, 2022, 07:16:25 pm
content: Ironically I have a video on YT with nearly a million views of me air soldering an IC while learning. Granted a standard pitch SOIC16 (IIRC).It's just been a while and I got a little cocky with the fine pitch stuff. There were warning signs. I decided not to bother setting up the microscope until after I'd made a mess. Tried to "wing" it with the magnifier stand. Then I didn't have my tweazers and this resulted in much dexterity with the point of a knife slid between two pins to be able to align it. ... and get burnt at least once. I did actually try and nudge the chip with my fingers while it was under hot air @350C. Recoiled back out of there before I got badly burnt!The lesson is to keep in practice and there are cheap options available... though I haven't looked.

author: DavidAlfa
author_rank: Super Contributor
timestamp: November 16, 2022, 08:37:54 pm
content: Align, solder opposite corners, never solder more than 2 pins in the align phase.Once it looks good, solder the other corners and start with the sides.Lots of flux, veeeery little solder in the tip, like 1/2 rice grain.Better solder from inside out, sliding will easily bent pins.

author: paulca
author_rank: Super Contributor
timestamp: November 17, 2022, 08:53:52 am
content: For those LFPQ adapter boards 0.5mm pitch. I would not add any solder on the first pass, after last night.The long pads to align different sized chips from 48 pin up to 100 pin have so much tinning solder on them once it melts and flows you will end up with a big glob of lead-free solder that contains no flux clogging the pins.On the second attempt I delibrately didn't add solder to the tip. I tinned it, cleaned it in the copper wool and used the solder on the pads already instead. As I said, placing the iron on the extended pad and sliding it against the foot of the pin caused the pad solder to wick up the pin. I think I had to add a tiny 0.5mm of 0.6mm solder to one side to get a dry looking couple of pins.On a normal board with normal foot print you will need solder of course.

author: Psi
author_rank: Super Contributor
timestamp: November 17, 2022, 10:14:37 am
content: With fine pitch LQFP and TQFP gel flux is a MUST and you will want somegood qualitysolder wick to remove any bridges.Flux will change it from "omg why does every pin bridge" to... "wow the solder is flowing like water and going exactly where i want it"Start by placing a little flux over all the pads on the PCB QFP footprint, just a tiny amount.Before placing the chip, add some solder on an end pad on some opposite sides.Now place the chip on top and touch those pins with a clean iron to melt that solder and allow the chip to sit down flat and be held in correct alignment.Now put a bead of flux over all the pins on a side to be soldered.Touch the first pin with the iron and add a little solder, it will bridge 1 or 2 pins, that's fine.Now quickly drag that bridge along the entire side of the chip with the iron while the flux is still active.(You will get the hang of how much solder you need to add vs what's too much)If you added to much solder then when you get to the end you will have a bridge or two.If you added the right amount you will have no bridges (most of the time)Use some solder wick to remove any bridges as needed.

author: Ground_Loop
author_rank: Frequent Contributor
timestamp: November 17, 2022, 11:32:32 am
content: Quote from: Psi on November 17, 2022, 10:14:37 amFollow these instructions, ideally under a microscope, and first time right with no bridges.

author: paulca
author_rank: Super Contributor
timestamp: November 17, 2022, 05:30:52 pm
content: Code:Target no device foundError in initializing ST-LINK device.Reason: No device found on target.Sniff. Sniff.

author: Lunasix
author_rank: Regular Contributor
timestamp: November 19, 2022, 09:20:14 am
content: I don't understand why you have problems with this type of package, they are very easy to solder (soldered hundreds).Use good solder (SnPb 0.25mm), good iron with not too small tip (Weller WS81 with LT-T for example) and good (and new) solder wick. Flux help if you have problems. And a microscope of course.Package like used for LAN9303, PN5321, TPS82150, XCL209F083DR (look if you want) seems to be impossible to solder by hand, but with a hot air gun and some practice, you can, and it is quite easy (I never use solder paste, soldered 10s of each).

author: Psi
author_rank: Super Contributor
timestamp: November 19, 2022, 10:30:28 am
content: The soldering iron tip can also cause problems.Usually happens when people buy the tiniest conical tip they can find which has almost no thermal mass and very small contact area.Something like a 1mm chisel or 2mm knife tip is ideal. Stay away from conical especially the ultra fine pointed ones.

author: paulca
author_rank: Super Contributor
timestamp: November 20, 2022, 08:52:26 pm
content: Second attempt I took my time and it went a lot better. Still managed to shift the chip at some pointThe only pin of concern is pin 4, but it's fine, checked under the scope.These are a little experimental. They were taken with a 200mm zoom lens with 35mm of Macro adapters.... from the far side of the room!You can zoom in on these forever too, before cropping (the first one isn't cropped) they are 24M Pixel.Just like a scope, the DoF with macro rings in tiny. You may be 6 feet away but the depth of field is tiny.

author: Ian.M
author_rank: Super Contributor
timestamp: November 20, 2022, 09:42:50 pm
content: Mask off the extra external pad length with Kapton tape, tack two corners and drag solder with plenty of flux, starting with the sides you didn't tack, and it shouldn't be *MUCH* harder than soldering it on the proper footprint. I probably wouldn't go as far as cutting away the excess pad length inside its footprint before soldering it.Your next problem is decoupling it properly - those long skinny traces are *NOT* your friend!

author: DavidAlfa
author_rank: Super Contributor
timestamp: November 20, 2022, 09:44:23 pm
content: C'mon it's not hard at all, just take your time, will go wrong if you speed it up.Took a TQFP100 STM32F407 sample I ordered a decade ago, aligned/soldered two corners, checked carefully before soldering more pins.Nothing will shift by magic, unless you think "looks okay!", solder everything, then realize it wasn't so okay.It's been a long time since I last soldereded a TQFP, yet look at the result.Sure, I had to tweak the position few times before getting it perfect, but took 2 minutes anyways.In your pictures it looks like you used too little to no flux? Will make miracles.(BTW, free samples, do you remember that?)Initial placement with some flux (Bottom slighly off):Soldering the corners:Finished & cleaned (There's some flux remaining between pins 13 & 14, not a short):

author: paulca
author_rank: Super Contributor
timestamp: November 20, 2022, 10:26:58 pm
content: Mine was flooded in flux, it's just that I cleaned it afterwardsI dont think it's difficult to do right. I also don't think it's difficult to completely mess it up and each mistake is harder and harder t fix.

author: DavidAlfa
author_rank: Super Contributor
timestamp: November 20, 2022, 10:33:44 pm
content: The golden rule is simple: Never solder more than 2 pins unless you're 1000000% proof it's properly aligned.Then solder the other corners before proceeding any further, otherwise it's easy to bend these only two pins holding the chip.Once all the 8 corner pins are soldered, it's really hard to mess the alignment upThe nightmare happens when a pin bends/moves and it was already soldered.Apply heat, push it with a needle... It almost always ends with damaged pins/pads/tracks!

author: paulca
author_rank: Super Contributor
timestamp: November 21, 2022, 08:31:48 am
content: In my case I tacked one corner, lost the alignment because my finger stuck to the flux residue. Reset just heating that one pin until I could move the chip off, then I cleaned that pad up and reset the alignment. Holding it this time with the point of a knife.It was fine after one corner, so I soldered down one untacked side. Looked grand. Moved to side two and my flux pen looked dry and here comes the mistake. I watched myself do it and went, "Ehhh...", knowing I might regret it. I pushed the flux pen nib down against the chip to cause the flux to flow. I recall seeing what I thought was tiny movement, but I wrestled with stopping, figured it was a bit late and soldered on. In hindsight. If a shove from the flux pen moved. A shove from the flux pen or a knife point would have moved it back.So it seems it did move when I pushed the flux pen against it. That was the mistake that caused the shift. In future I can pump the flux out against a bare bit of board and not up against the chip!

author: paulca
author_rank: Super Contributor
timestamp: November 25, 2022, 11:59:02 am
content: The chip works.Can't for the life of my get the SysTick to fire. I have had this before when configuring the clock without an HSE in CubeMX, the SysTick is broken. That's fine. I confirmed at least a GPIO blinks an LED, just that I can't use HAL_Delay() without a hard fault.

author: DavidAlfa
author_rank: Super Contributor
timestamp: November 25, 2022, 02:21:40 pm
content: Systick always worked for me in hse, hsi, whatever.I eemember once where I accidentally disabled systick, or CubeMX didn't enable it under SYS tab, but nothing else.Again, ranting without providing anything, no worries, I'm taking the magic glass ball again, give me a moment

author: paulca
author_rank: Super Contributor
timestamp: November 25, 2022, 06:42:46 pm
content: I moved on. In the past it has been the systick not being setup properly by hal. I haven't spent enough time investigating to warrant a request for help yet. I was just a report. I have 16Mhz xtals here if it comes to that.

author: paulca
author_rank: Super Contributor
timestamp: December 10, 2022, 07:56:58 pm
content: I wonder the prospects of this one working. It did all seem to go far, far too smoothly and fairly quickly. Hot air of course. I'll edit up a video later maybe.

author: DavidAlfa
author_rank: Super Contributor
timestamp: December 10, 2022, 08:14:31 pm
content: There's a really small difference between the naked MCU and the 411 Black Pill board, why do this?

author: paulca
author_rank: Super Contributor
timestamp: December 10, 2022, 08:33:59 pm
content: Quote from: DavidAlfa on December 10, 2022, 08:14:31 pmAt some point I'm going to put one on a board. I won't be using the blackpill forever. Besides, I want to know if they work or are fake.There is one significant difference. Size. If I want an MCU in a product handling one or two peripherals I don't need a whole BlackPill board sized PCB to do it, though they are handy for prototypes.And why not?

author: paulca
author_rank: Super Contributor
timestamp: December 12, 2022, 01:39:40 pm
content: ... and no. It didn't work. No response to programmer. It's not shorted out, it's consuming power, but no response.Three options.1. The chip is indeed a fake.2. My test harness is missing something or incorrect.3. The foot print on the DIP adapter board was not exactly correct for the chip. The foot print specced by KiCad for example has a much smaller central pad area. When you look at a lot of similar "no lead" chips the central pad is also quite small. However on this STM32F4 the central pad covers the entire bottom of the package with barely a 0.5mm gap between the pins and the ground pad. My expectation is I have bridges under the chip between a pin and the ground pad. Probably not a power pin, but a pin none the less.I might revisit it when I get a chance again. My bets are on option 2 or 3 above. For instance. The breadboard I was using as the test harness has now been angrily thrown in the bin after becoming a fizzling/fissling/partial connection mess. The strips have zero grip and make dodgy contacts all the time. This will not be welcomed by a bare MCU. So I should at least give it a chance on a proper board. Maybe even solder some 100nF directly to the VDD pins for decoupling.... and David... I know. That's why the V1 prototype looks like this:

author: DavidAlfa
author_rank: Super Contributor
timestamp: December 12, 2022, 03:52:32 pm
content: Don't make obvious things obvious, you're using a tqfp adapter, so no final prototype or size contrains at all.Ah yeah, it doesn't work, maybe it's because every pin has 2-inch trace to the nearest component, including the decoupling caps...Stm32 are laser-engraved, that one looks painted - expected from AliExpress.

author: paulca
author_rank: Super Contributor
timestamp: December 12, 2022, 04:27:51 pm
content: Quote from: DavidAlfa on December 12, 2022, 03:52:32 pmIt's engraved, it too ages to get the light on it right for the engraving to show up.I'll try soldering the decouply caps to the adapter board. In fairness that's what I did to the F411RE and it worked.The tqfp adapter isn't for the final prototype(s), its practicing soldering so when I come to adding 2 or these to a board I'm not completely new to it and ruin a whole board.Granted I could start with cheaper and easier to test chips. In parallel I do want to know if these are fake. Again no point waiting till I solder one to an actual project PCB to find out.

author: DavidAlfa
author_rank: Super Contributor
timestamp: December 12, 2022, 04:47:44 pm
content: Start by measuring every pad, setting the DMM in diode mode, positive to gnd and the negative to each pin, you should get 400-600mV from the pin ESD diode.If the bottom pad is shorting something, remove the chip and put some Kapton tape to it, otherwise check the wiring, also you should know already you need several caps for Vdd/vdda, reset and **specially** VCAP pin.