I learned a lot today... - Page 1
Forum section: electronics / general

author: Unknown
author_rank: Unknown
timestamp: June 25, 2013, 12:51:09 am
content: I learned that I have lead free solder.I learned that my solder is too thick for a 0.5mm QFP.I learned that it's really easy to short a QFP with lead free solder.I learned that lead free solder doesn't melt easily.I learned that I need a higher quality tip for my soldering gun.I learned that I wasted about $9 and probably ruined a chip.I learned that positioning a QFP chip is nearly impossible.... I learned that I still have a lot to learn.But at least I fixed my oscilloscope probe's ground with a bit of solder and heat shrink tubing. There's that.

author: c4757p
author_rank: Super Contributor
timestamp: June 25, 2013, 12:52:50 am
content: Quote from: duskglow on June 25, 2013, 12:51:09 amQFP? Nah... fine tweezers, magnification, and no caffeine in the past six hours. You can do it

author: PeterG
author_rank: Frequent Contributor
timestamp: June 25, 2013, 12:55:42 am
content: SIX hours without caffeine? Is that even possible?Regards

author: Unknown
author_rank: Unknown
timestamp: June 25, 2013, 12:56:17 am
content: I'm going to Fry's to get some thinner 60/40 solder and some higher quality tips, and I'm hoping that that will seal the deal. I did learn that I can gently hold the QFP in place with some vice grips long enough to get the solder on the leads.And I do't do caffeine at all, I'm high strung enough without it.

author: c4757p
author_rank: Super Contributor
timestamp: June 25, 2013, 12:58:04 am
content: Quote from: PeterG on June 25, 2013, 12:55:42 amI say I've been "without caffeine for X hours" when it's been X hours since my last full pot of coffee. Individual cups don't count.

author: lgbeno
author_rank: Frequent Contributor
timestamp: June 25, 2013, 01:27:28 am
content: Quote from: duskglow on June 25, 2013, 12:51:09 amSolder gun? Hopefully it's a iron that you hold like a pencil...Best bet for hand soldering QFN is to put a large via in the center heatslug then you can solder the pads first and fill in the via from the bottom side. Leaded solder is better but lead free is doable using this method.

author: c4757p
author_rank: Super Contributor
timestamp: June 25, 2013, 01:28:13 am
content: QFN, or QFP?

author: nanofrog
author_rank: Super Contributor
timestamp: June 25, 2013, 03:09:05 am
content: Quote from: c4757p on June 25, 2013, 12:52:50 amI wish it were that simple for me... Caffeine or not, my hands always shake.

author: c4757p
author_rank: Super Contributor
timestamp: June 25, 2013, 03:14:14 am
content: Mine do too, but I can usually find at least one position to rest them in that makes it minimal. Put a lot of pressure on the table with the rest of your hand.

author: Unknown
author_rank: Unknown
timestamp: June 25, 2013, 03:54:28 am
content: OK, I had fine tweezers, magnification, very fine solder, a very fine solder tip... and for some reason, I can't seem to not bridge the little legs.And then the wick is utterly useless at unbridging them, so I have to pull it off, carefully yank the solder out, recenter it... and promptly bridge them again! Sigh.

author: c4757p
author_rank: Super Contributor
timestamp: June 25, 2013, 04:19:31 am
content: There's a word that appears to be woefully missing in this whole thread:FLUXDrown the pins in it.And the wick too, if it doesn't have any. (That's an easy one. Wick with flux: Smells good when you heat it. Wick without flux: Makes you want to kill yourself.)

author: IanB
author_rank: Super Contributor
timestamp: June 25, 2013, 04:24:42 am
content: You don't use braid to remove solder bridges. Braid is for desoldering parts or for cleaning up pads on the board.To remove bridges just apply a little flux to the work and touch the clean tip of the iron against the excess solder. The iron tip will suck up the solder like magic.Watch some soldering videos like the ones from Pace or Hakko for good advice and guidance.

author: Unknown
author_rank: Unknown
timestamp: June 25, 2013, 04:25:29 am
content: I wonder if I have a bad tip. It's not sucking up solder, the solder's balling up on it. I can't even tin it.

author: IanB
author_rank: Super Contributor
timestamp: June 25, 2013, 04:26:29 am
content: Then it's not a bad tip. It's a crap tip. What kind is it?Was it tinned when new?

author: Unknown
author_rank: Unknown
timestamp: June 25, 2013, 04:28:26 am
content: It's the kind that came with my rework station. I was already thinking I should get some genuine hakko, now I REALLY think that.It wasn't tinned, it was just solid metal, whatever the metal was.

author: Bored@Work
author_rank: Super Contributor
timestamp: June 25, 2013, 04:42:48 am
content: Quote from: PeterG on June 25, 2013, 12:55:42 amIs that even legal?And kids remember, flux is no substitute for coffee.

author: Unknown
author_rank: Unknown
timestamp: June 25, 2013, 07:27:47 am
content: Whew, I got it, finally. After maybe ruining a couple of chips. I fluxxed the hell out of it (that helped, thanks), learned that a very little bit of solder will go a long way, bumped the temperature 50C, and figured out that even if the wick won't remove the solder bridges, a solder sucker will. Think I ruined a few rather expensive chips, but it was a good learning experience, so I suppose it was worth it... guess I should order a few more. I'll do it again tomorrow with another QFP board, just to make sure I got it right. I think I may be able to salvage the other chips, but sigh.Thanks for letting me vent, this was exceedingly frustrating. But I guess it's the only way you learn. This is literally the first SMD QFP I've ever soldered, and I had to choose one with 0.5mm pitch to start...

author: AndyC_772
author_rank: Super Contributor
timestamp: June 25, 2013, 07:50:31 am
content: It sounds as though the problems you had were nothing to do with the pitch of the device, they're almost entirely down to the quality of tools and materials you have available. Soldering a 0.5mm QFP is really quite straightforward if you have the right kit:- liquid flux. Use plenty, but not so much that boiling it off draws all the heat out of the tip.- a tip that's clean, not too small, and properly tinned. You should be able to pick up a blob of solder about the size of the head of a pin, and it should wet the surface of the tip and stick to it immediately. If the solder forms a round ball on the tip, clean the tip, and if that doesn't work, bin it and get a new one.- avoid very small, pointed tips, as they don't hold enough heat. I prefer a chisel tip about 1.0 to 1.5mm diameter.- if you don't have one already, get a tip tinner/cleaner block - basically powdered solder in a resin matrix.- the proper technique for a QFP is called "drag soldering", and it's much easier and gives a much better result than trying to solder every pin individually. I'm sure there will be videos on Youtube.

author: Unknown
author_rank: Unknown
timestamp: June 25, 2013, 07:56:15 am
content: The pitch of the device didn't help, but it wasn't too bad once I got it figured out. I'm pretty good at soldering most things, but as with everything in electronics, there are big gaps in my knowledge that I'm working on closing. Things like how to solder *right* is one of them.

author: BravoV
author_rank: Super Contributor
timestamp: June 25, 2013, 08:54:09 am
content: Quote from: duskglow on June 25, 2013, 04:28:26 amYou should get a proper iron, especially a genuine tip, its like night and day. On a proper tip, once cleaned properly, the molten solder will actually flow and sucked into the tip nicely.For an example, just watch the little nice video at the bottom at this page and see how the molten solder stays and sticks at the coated tinned area of the tip ->http://www.hakko.com/english/maintenance/topic_difference.htmlAbout tip shape, my personal favorite is sharp knife style, its perfect for these tiny pitch pins, here is a really good example ->http://www.hakko.com/english/tip_selection/type_k.html, there are many small videos in this page demonstrating the use of this knife style tip, for example like this one ->Here, highly recommended to watch them all at that page.Edit :On Hakko's various tip styles, the knife style is the most efficient for the heat transfer, hence its also has the best heat regulation compared to other styles, posted this at other thread ->Here

author: nctnico
author_rank: Super Contributor
timestamp: June 25, 2013, 04:25:13 pm
content: Quote from: duskglow on June 25, 2013, 04:25:29 amThat sounds really bad. You need a temperature controlled iron at 330deg Celcius and a big tip. People often tend to use a tip which is too small. I usually solder 3 or 4 pins of a QFP at the same time.

author: Unknown
author_rank: Unknown
timestamp: June 25, 2013, 08:44:23 pm
content: Took all of your advice - lots of flux, blade tip, and the second one went really smoothly. Still some stuff to learn but I'm proud of this one.

author: c4757p
author_rank: Super Contributor
timestamp: June 25, 2013, 08:46:52 pm
content: Not bad!

author: Unknown
author_rank: Unknown
timestamp: June 25, 2013, 08:50:13 pm
content: Not perfect, but there are no shorts and a spot check shows good continuity on random pins... so now I can get to prototyping.... and I think I need to order more chips.The other one works, but looks way more rough. I'll use this one first and use the other as a backup.

author: Galaxyrise
author_rank: Frequent Contributor
timestamp: June 25, 2013, 08:59:33 pm
content: What kind of liquid flux is good for that? I've got something likehttp://www.circuitspecialists.com/835-100ml.htmland it leaves this dark crust behind that I either ignore or have to chip off with a knife/screwdriver.

author: Unknown
author_rank: Unknown
timestamp: June 25, 2013, 09:00:38 pm
content: I used a radio shack gel flux. To clean it off, I used a 91% isopropyl alcohol I bought from the grocery store. Came right off. You can still see a little bit under the chip where I couldn't reach.

author: nanofrog
author_rank: Super Contributor
timestamp: June 25, 2013, 10:06:53 pm
content: Quote from: c4757p on June 25, 2013, 03:14:14 amSadly, my attempts to do so haven't turned out nearly as well as I'd like (pressure on the edge of my hand and it still rocks back and forth <sliding the tip parallel with the pins>). Lots of flux does help prevent bridges though, so it's not impossible for me to do.Comical to watch I would imagine, but it does get frustrating from my POV.Quote from: duskglow on June 25, 2013, 08:50:13 pmLooks good from what I can see in the pic.Quote from: Galaxyrise on June 25, 2013, 08:59:33 pmThat's good flux. I use an equivalent from Kester (186) as it has less solids (doesn't make quite as much of a mess). Either can be left on if you wish, but does look better if you clean it (just be thorough, or you can end up leaving active residues that cause corrosion).Under the pins can be addressed by using Q tips or plastic brushes (examples:http://www.ebay.com/sch/i.html?_trksid=p2050601.m570.l1313&_nkw=esd+brush&_sacat=0&_from=R40).

author: Unknown
author_rank: Unknown
timestamp: June 25, 2013, 10:17:09 pm
content: A question: What kind of headers would be best to solder onto it for prototyping purposes? Female or male?I have male readily available but that makes connecting to a breadboard a little more difficult, because there's no easy way of plugging it directly onto the breadboard, so I have to use extension wires.

author: nanofrog
author_rank: Super Contributor
timestamp: June 25, 2013, 10:33:08 pm
content: Quote from: duskglow on June 25, 2013, 10:17:09 pmPerhaps something like this would help?http://www.ebay.com/itm/20-jumper-interface-pin-header-for-breadboard-pcb-/250462447737?pt=LH_DefaultDomain_0&hash=item3a50b9a879

author: Unknown
author_rank: Unknown
timestamp: June 25, 2013, 10:36:17 pm
content: So with those, I could make both male AND female connectors at the same time? Male through the top, female on the bottom?

author: nanofrog
author_rank: Super Contributor
timestamp: June 26, 2013, 04:48:07 am
content: Quote from: duskglow on June 25, 2013, 10:36:17 pmOnly need one or the other I would think (male or female). Figured the female versions would be a bit more versatile, as you can solder directly to the board's TH's and/or use wire and make a jumper as needed.This is based on your board appears similar to an SMT to DIP type adapter board to me (presumes the spacing is right they line up with the breadboard socket holes). Assuming this is the case, tuck the larger diameter end of the pins from the bottom on two opposite sides. Then use wire terminated to pins for the others.You could lay the existing board on your breadboard and see if 2x rows of holes mate up with the BB sockets to check the spacing first.Hope this helps.

author: Galaxyrise
author_rank: Frequent Contributor
timestamp: June 26, 2013, 05:57:48 am
content: If you tried to solder those pins to a PCB, I suspect there wouldn't be enough of the male end would be sticking out the bottom to mate it to anything else. They're not really sticking out of that breadboard enough for the pins to be that long.

author: Unknown
author_rank: Unknown
timestamp: June 26, 2013, 06:02:45 am
content: Another potential issue is that the chip actually contains, I believe, four different VCC/GND pairs, and each one needs its own decoupling capacitor. I'm probably going to put those on the top of the board, because putting them on the breadboard kind of defeats the purpose. I may even join them on the board itself so that I don't end up feeding four different pairs of wire to the chip.Depending on the complexity of the circuits required, EG reset, etc., I'm really considering making a bottom board that any headers are connected through so that I can put all of the stuff that's inviolable onto the board itself. What do you think of this approach?I'm meaning, the reset circuitry, the oscillator, decoupling, etc.

author: nukie
author_rank: Frequent Contributor
timestamp: June 28, 2013, 01:05:27 pm
content: I counted 10 posts then the word FLUX appeared. It's the key component to soldering fine pitch leads. Some thin solder for eg 0.3mm is worst, they contain too little flux.Next, make sure you use lower temperature so the flux don't get burned fast this also prevent the IC from over heating. You don't need a lot of thermal power to solder these fine pitch leads. Finally you don't really need special tips, just use one which is not overly large for the leads.