FPGA/CPLDs that are hand solderable - Page 1
Forum section: electronics / general

author: Frozen001
author_rank: Newbie
timestamp: January 19, 2022, 03:06:31 am
content: Sort of a rant/vent here, but with the ever shifting toward smaller devices, it is getting harder and harder to have a decent electronics hobby simply because we cannot actually mount parts to the PCB anymore, or at least it is getting difficult. I want to build something with a CPLD or FPGA, but the "easiest" to mount device that I can find in stock and free development software is a 100 pin TQFP package. If this tend keeps up, we soon will not be able to build anything as a hobby any more without having to have an assembly house mount these parts, which can up costs significantly, especially if I want to build 1 cca.

author: Someone
author_rank: Super Contributor
timestamp: January 19, 2022, 03:28:42 am
content: Buy a dev board or System on Module (SoM), they are targeting exactly that market of low volume low barrier FPGA use.

author: asmi
author_rank: Super Contributor
timestamp: January 19, 2022, 03:31:40 am
content: I make boards with FPGAs in larger-pitch BGA packages at home without any problems. This is the reality of situation - if you want anything high-speed, you will need to embrace BGAs. You can stick to old mostly obsolete or slower parts, but it will only get you so far. Thankfully, tech required to use these BGA packages is also becoming more and more accessible - like multilayer boards now being super-cheap, existance of KiCAD with good enough features to design some high-speed boards (see project in my signature as a proof positive), cheap tools like stereo microscopes and hot air guns available on a market. Just about a decade ago all that stuff cost a pretty penny, but now it's like $100 for the hot air gun and $150 for the stereo microscope. And these tools will last many years, so it's a one-time expense.Or do asSomeonesays. These are going to be more expensive, but there is less upfront cost of purchasing equipment.

author: betocool
author_rank: Regular Contributor
timestamp: January 19, 2022, 09:49:56 am
content: Usually PCBWay and the like offer to reflow components on a PCB.If you have 5, and send them the chips (or they can get them for you), the extra cost for "assembly" is about 30 - 50 USD or so. Worth asking if you don't have the tools.You can populate the rest per hand.Cheers,Alberto

author: Bassman59
author_rank: Super Contributor
timestamp: January 19, 2022, 03:08:51 pm
content: Quote from: Frozen001 on January 19, 2022, 03:06:31 am0.5mm pitch TQFP is easily soldered by hand.

author: nctnico
author_rank: Super Contributor
timestamp: January 19, 2022, 04:33:31 pm
content: Quote from: Bassman59 on January 19, 2022, 03:08:51 pmYes. And QFN as well (with vias in the pad under the chip so it can be soldered using hot air).

author: NorthGuy
author_rank: Super Contributor
timestamp: January 19, 2022, 04:44:38 pm
content: I am very clumsy, but even I can hand solder pretty much anything.

author: SiliconWizard
author_rank: Super Contributor
timestamp: January 19, 2022, 06:51:04 pm
content: You need a microscope for fine-pitch SMD. Otherwise it's like shooting in the dark, even if you have excellent eyesight.BGAs are an exception though, since even with a microscope, you wouldn't be able to see anything much. So what you need is some good flux, some technique and a hot air gun, or a hot plate, or a mix of both, or a reflow oven if you can afford that (you can find small affordable ones these days...)I personally do not like QFNs. They are the most annoying to hand solder reliably, unless you can use a stencil. Just my opinion though, as apparently some people can handle them with one hand and eyes shut.But for hobby stuff, as Someone said, you can go the dev board/breakout board/SoM/... route. Sure not every component will be available in this form, but still a lot can be done.As to the future of all this, having no crystal ball, I don't know. Is the hobbyist market going to disappear altogether one day? Are conventional PCBs going to themselves be obsolete (and replacement tech going to be completely out of reach for hobbyists)? Who can tell.

author: nctnico
author_rank: Super Contributor
timestamp: January 19, 2022, 07:46:29 pm
content: Quote from: SiliconWizard on January 19, 2022, 06:51:04 pmThe trick is to have the pads extend further away from the QFN package so you can reach them with a soldering iron. The recommended footprints are usually no good for hand soldering. During soldering use a big tip and lots of flux. The worst mistake to make when soldering QFP or QFN is trying to solder each pin. Instead, solder 3 or 4 pins at the same time (look up drag soldering).

author: Martin Miranda
author_rank: Regular Contributor
timestamp: January 19, 2022, 08:20:00 pm
content: https://www.latticesemi.com/Products/FPGAandCPLD/MachXO2

author: asmi
author_rank: Super Contributor
timestamp: January 19, 2022, 08:36:28 pm
content: Quote from: nctnico on January 19, 2022, 07:46:29 pmNo need for any of that. Simply pre-tin the pads, add some tacky flux, place a part and start heating with a hot air gun. It will probably take a few attempts until you master this approach, but once you do, it will become super-easy from that point on. Just make sure you keep your heat gun far enough to not blow the part away, nor to blow away neighboring components (you can protect them with a capton tape if you need to, but usually it's not required).

author: asmi
author_rank: Super Contributor
timestamp: January 19, 2022, 08:54:28 pm
content: Quote from: SiliconWizard on January 19, 2022, 06:51:04 pmLike I said above, just invest some time once into mastering this, and it won't ever be a problem for you in the future. Just get some cheap QFNs to practice if you don't have any already, and get cracking. It will only take a few tries until you get a hand of it.Quote from: SiliconWizard on January 19, 2022, 06:51:04 pmIt won't disappear as long as there will be enough people willing to do it, which will probably never happen. The exact nature of it will likely change though, as the industry is trending towards miniaturization and ever higher interface speeds, so BGAs will become more prevalent as the time goes on.

author: Mario87
author_rank: Frequent Contributor
timestamp: January 26, 2022, 09:28:47 am
content: Personally, I find the hand soldering of smaller / more challenging components to be some of the best part of a project. Maybe I am just strange like that

author: NorthGuy
author_rank: Super Contributor
timestamp: January 26, 2022, 04:00:16 pm
content: Quote from: asmi on January 19, 2022, 08:54:28 pmWith QFNs, putting the correct amount of solder on the center pad is key. If you put too much, the chip will tilt one side and the pins on the other side will be left in the air. If you put too little, the solder on the center pad will suck the chip down and it won't self-align. It is easier to do with biggish QFNs (i.e. 20+ pins), but I often struggle with very small 0.4 mm parts.If you use solder paste, you get better control of the solder quantity. In this case, QFNs are one of the easiest, way better than TQFPs. As stencils gets cheaper and better, solder paste becomes more advantageous than hand soldering.

author: asmi
author_rank: Super Contributor
timestamp: January 26, 2022, 04:23:45 pm
content: Quote from: NorthGuy on January 26, 2022, 04:00:16 pmYou can't use stencil for rework, and it's just a matter of time until you will come across a dud of a QFN (or kill it due to schematic/layout/handling/testing screw-up) and will need to replace it. This is why I strongly recommend mastering hand-soldering without any solder paste and stencil, this way it just won't be a problem at all. For me it took about 5 or 6 attempts to get a hand of it, larger QFNs are actually harder to solder/desolder because it's harder to heat it up uniformly such that the whole thing reflows at the same time. Preheat can help with it, but I don't use it for practical reasons (it's hard to use it with microscope and not get burns), so for me smaller QFNs are easier.

author: woofy
author_rank: Frequent Contributor
timestamp: January 26, 2022, 04:42:22 pm
content: For soldering small QFNs on prototype boards I place a largish (iron tip size) PTH hole in the center under the pad. Then after soldering the outside pads, just pop the iron in the center hole and solder that down.I use that trick for LAN chips where the center pad is the only ground pin on the chip.

author: nctnico
author_rank: Super Contributor
timestamp: January 26, 2022, 09:16:29 pm
content: Quote from: NorthGuy on January 26, 2022, 04:00:16 pmWhat works really well is to simply put non-tented vias in the exposed / thermal pad to wick away the excess solder. You'll need those anyway and they allow for hand soldering a QFN as well. Add flux and use hot air to heat the board. Solder will wick through the vias to the exposed pad. Works like a charm.