current state-of-the-art in budget home reflow? - Page 1
Forum section: electronics / general

author: djacobow
author_rank: Super Contributor
timestamp: July 03, 2019, 12:59:17 am
content: tl;dr:Is there a "DS1054Z" of reflow equipment?Longer:I need to assemble a bunch (~200) of largish (150mm x 150mm) boards of moderate complexity (40 unique parts, 150 parts), all SMT. However, I'm not in a rush -- I have 4 months plus a bit to do this run.I've always assembled prototypes with an iron, but am thinking it's time to take my SMT capabilities to the next level and start using reflow. I've gotten PCBA quotes which just won't work for this particular project.So I started researching reflow techniques and I have to say, I'm a bit lost. The T-962 and its infrared cousins are the right price but they seem to have a lot of problems. Some of those problems are ameliorated by firmware and control board upgrades and other hacks, but 1) I'm not really all that interested in hacking my tools and 2) some of the problems seem pretty much inherent with infrared heating from a few discrete elements. I also just cant tell if these units work well on bigger boards. Every demo video I see is of some 2"x3" doodad. Then I read reviews that say the board edges from larger boards go uncooked while the middles are incinerated and ... I don't know.I also started looking at hot plates / preheaters, thinking I could abuse them for reflow. I sort of like the idea of this thing:https://www.tindie.com/products/LafrasH/modern-electronics-reflowr-v2.It looks like the larger one could work for my purposes but not without modification (such as countersinking the top screws to use the entire area. Also, teardowns show dubious build quality.Is there another category of device I'm missing? I'd be willing to spend $1000 but not $2000. Space is a factor. Not having to buy and gut a toaster oven, then tweak it repeatedly is also a factor.Is there anything else out there that I should be looking at?

author: mrpackethead
author_rank: Super Contributor
timestamp: July 03, 2019, 06:36:17 am
content: Vapour Phase Reflow.

author: jmw
author_rank: Frequent Contributor
timestamp: July 03, 2019, 08:45:35 am
content: I've done a toaster oven conversion using the kit from Whizoo and I'd do that again in a heartbeat having also used a modded T962. The type of oven they use in their build guide is easily obtainable in the US and the total materials price is well under $1000. There aren't turn-key options in this price range that aren't mediocre or plain crap, so DIY at least gives you some control over the result. 4 months is way enough time to squeeze in the work to build it - I think I split the work over 3 days in one week. I have not had to make any subsequent tweaks - the oven worked well and exceeded their nominal inertia and insulation specs out the gate.I'd consider the vapor phase route if starting today but there's no canonical build guide and kit.

author: mrpackethead
author_rank: Super Contributor
timestamp: July 03, 2019, 10:10:58 am
content: Quote from: jmw on July 03, 2019, 08:45:35 amGetting close.https://www.eevblog.com/forum/manufacture/practical-diy-or-modest-cost-vapor-phase-does-it-exist-yet/

author: Kean
author_rank: Unknown
timestamp: July 03, 2019, 03:54:43 pm
content: I've tried all the usual things over the last 10 years.I started with just the soldering iron, and then hot air reflow (a slow process). Moved to an old Sunbeam frypan for single sided PCBs, and it works well and I still use that. Never bothered with a controller, just a thermocouple JB welded on the base and keep an eye on it.I recently tried a AliExpress hotplate and it looks workable - see the 946C or 946D, under various brands like Yihua or Youyue, but easiest to just search on those model numbers. Mine is a 946D for LCD separation, and the 946C is meant for SMD preheating.See this twitter threadhttps://twitter.com/KeanM/status/1143837495836065794I bought a toaster oven, but never got around to modding it. I do use it for other applications like part baking.I have a T962A oven with the modified firmware - and yes it has somewhat uneven heating. You have to customise your profile to your particular PCB, especially larger or panellised PCBs, or ones with large copper areas. You also need to tune it for PCB colour (e.g reflective white vs dark absorbing colours), or for larger components that need extra heat. All of that is a real pain if you're only doing a few boards, leading to many unhappy users. But if you are planning a batch of 200 like you mention it should be possible, and worth the time, to tune it in. People have successfully used it, including me to some extent. I've probably done a few hundred PCBs with just a few burnt connectors, and occasional extra hot air reflow needed. A toaster oven may give similar or superior results with a bit of work.After all those experiences, I'm now looking to do a vapour phase trial - and I'm following along with mrpackethead's post (see above). My contract assemblers tend to use VP for smaller runs, although they've noted about more tombstoning problems compared to the proper reflow conveyor.I have to recommend against dealing with Lafras Henning. I did help with a review of his Reflowr (with MickMake), and while it worked OK, the build quality was a bit dodgy and no better than the above heated plates. Software was pretty crap too. But worse was the way he has treated his backers on Indiegogo, with many not receiving their rewards while he was apparently happily shipping units to Tindie purchasers. And then he basically just stopped replying. Not the kind of seller I would want to deal with. His other campaign for an injection molding machine had an even worse outcome - and people put down serious money on that.https://www.indiegogo.com/individuals/11729630/campaigns

author: djacobow
author_rank: Super Contributor
timestamp: July 03, 2019, 05:00:53 pm
content: Thanks for the summary, Kean.The good/bad news is that it looks like I haven't missed any major/obvious great solutions.I keep looking at the oven / controleo approach and I just get stuck on the modding part. Not that I can't do it, it's just that I like designing and building electronics, and cutting up cheap sheet metal toaster ovens is not a hobby interest of mine. (EDIT: I see Whizoo has completed ovens available for $989. Interesting!)One thing you might be able to answer: can you even do lead-free on the hot plates? They certainly seem cheap enough that I can afford to experiment.Thanks for the steer on Lafras. I wrote to him with some questions about the reflowr and the answers made it clear that his specs were misleading. That was a turn-off right there.

author: Kean
author_rank: Unknown
timestamp: July 03, 2019, 06:12:22 pm
content: Quote from: djacobow on July 03, 2019, 05:00:53 pmI use GC10 paste and have no issues, but I believe any lead-free paste that comes in contact with the hot plate will likely cause some damage over time. I see more and more pitting on my aluminium fry pan. Not a big deal, as you won't be cooking your morning breakfast on it, but probably should clean it occasionally with a scotchbrite pad to avoid any build-up of crud.QuoteInteresting! I generally don't like to speak ill of anyone, but he burnt his own bridges. The evidence is there to see if you know where to look.

author: mrpackethead
author_rank: Super Contributor
timestamp: July 04, 2019, 07:05:08 am
content: Quote from: Kean on July 03, 2019, 03:54:43 pmThis is what i love about VP. You just dont' have to worry about the profiling. It just works. :-)QuoteVP has a bunch of advantages, but there are some down sides. the tombstoning is one of them. Theres lots of papers on the reasons, but i can tell you a few things that you will find will help.(a) Think about your board design. Thermally balanced pads are important.(b) Consistent paste application. I now ( even for ptorotypes ) always use a Stainless Steel stencil. At $15, its just not worth my time to fart around.(c) Use of a paste that works well with Vapour Phase. One where the tackiness of the flux stays pretty consistent through the reflow process. I find that Henkel GC10 works really well, I've used a couple of other pastes, and had considerably more issues.

author: Kean
author_rank: Unknown
timestamp: July 04, 2019, 06:54:25 pm
content: Quote from: mrpackethead on July 04, 2019, 07:05:08 amAgreed re stencils. While I started off with a manual (air driven) paste dispenser, I now normally get an unframed stencil with any prototype PCB order, and a framed stencil when I order more boards for production. The real cost of the stencils is somewhat higher because of shipping (I'm typically using JLCPCB and DHL), but my time is more valuable to me and my customers.Things are way different to the days of paying $600 for a stencil, although I expect larger contract manufacturer still want that for the stencils they use in semi/fully-auto printers for mass production.Regarding GC10, I've been surprised how few small contract manufacturers know of it. None of the ones I've dealt with use it, and generally they give me blank looks when I suggest they try it.

author: jmelson
author_rank: Super Contributor
timestamp: July 07, 2019, 04:45:31 pm
content: Quote from: mrpackethead on July 04, 2019, 07:05:08 amI've done over 2000 boards with my homebrew toaster oven/thermocouple controller, and have had, MAYBE, 5 real tombstone parts in that time. I have had a small number of half-soldered passive parts (head in pillow type defect).Maybe a tombstone is better, as you can't miss those, while the failure of one end to solder is harder to detect.I can also recommend GC10 (sold in US through Loctite), it is VERY VERY good in IR reflow, too. I've used a bunch of other pastes, and had a LOT of issues with incomplete soldering of PQFP/TQFP components. GC10 and a paste from Warton Metals in England have performed the best.Jon

author: djacobow
author_rank: Super Contributor
timestamp: August 01, 2019, 07:37:41 pm
content: So, given my budget and (lack of) taste for adventure, I ordered the T962A. I did the the masking tape to kapton thing, the chassis ground thing, and put in the Unified Engineering FW. Did not do any of the cold junction stuff or other mods.After one day with it, I am not super thrilled. I have a board I'm working on, about 12 cm x 15 cm. I was able to do leaded reflow with that on a hot plate quite successfully, and this oven seems about as effective, but with more noise.However, with the hot plate, I could not do lead free without scorching the soldermask, at least a bit. I'm using TS391SNL50 paste. In the new oven, my first board didn't reflow at all using the lead-free profile that was on there that just peaked at 250. I used the custom profile to extend the 250C time for three or four more "dots" (30 seconds each?) and I started to get reflow around the edge of my board, but not in the center. I increased the heat and time a bit more, and still no dice. Boards were coming out with the flux burned off and the paste turned into cement, but not reflowed.These boards have > 100 parts on them, all hand placed, so after three failures I was starting to lose my sh$t, so to speak. Finally, I put two machine bolts on the tray to elevate the board and thermally isolate it from the tray. This time, I got reflow and the next couple of boards looked fine, though one of them had a Vcc/Gnd short that I could not track down after a lot of trying, so ended up scrapping that one, too. I think it's probably a short under a decoupling cap.I'm obviously a beginner at this, and scientifically, I've screwed up by changing two things (oven and to lead free) at once. I'm not sure which one is giving me more trouble. The lead free seems much less forgiving of a blob of paste that might bridge two pads. With the leaded stuff I was using, the past just spit up and I had no problems, but with this partly-reflowed lead-free, I end up with a conductive concrete paste blobs in bad places.In other news, if I reheat "dry" paste, is there any hope for it?

author: asmi
author_rank: Super Contributor
timestamp: August 01, 2019, 08:10:41 pm
content: Always raise your boards above the tray in that oven, as the tray is a giant heat sink that can soak up a ton of heat off board. This is especially so for multilayer boards with large ground and power planes, and those can soak up quite a bit of heat as well. I generally use standoffs made out of M3 screws, or just a bunch of old PCBs if the board I'm reflowing doesn't have any mounting holes.As for dry paste, it will not reflow properly because there will be no flux which greatly affects solder wetting ability, so you will risk getting cold joints and a "head in the pillow" problem in case you use BGAs.Finally I would definitely recommend you to do a cold junction compensation mod as this will greatly improve repeatability of reflows. Without this mod the firmware assumes certain "base" temperature, and it's close enough to it when the oven has been just turned on, but after a reflow or two this will not be the case anymore, and thus the firmware will "think" that temperature is far from what it actually is.

author: djacobow
author_rank: Super Contributor
timestamp: August 02, 2019, 04:05:01 am
content: The cold junction thing isn't too much trouble, so I might as well do it.I did a few more boards today and had similar results. The boards were not reflowing properly near where the boards were held up on the bolts. I suspect that even though the board is really only in contact with the bolts in a small spot, perhaps that was enough to suck away the heat. I also tried just putting the boards up on two or three 1/4 nuts on the tray. They also stopped reflowing in their vicinity, but with careful placement, I was able to avoid having them near anything.I'm going to try to find something to hold up the board that is not heat conductive and not burnable. Some kind of tiny ceramic pyramids might be nice for the purpose.But anyway, I will soldier on tweaking. Can try different paste, difference curve, different support. I also wonder if my board is particularly difficult. It is very complex shaped with lots of internal cutouts. It is also white. Does a white board get cooked less because it reflects IR, or does it get cooked more because somehow it tricks the oven into thinking it is colder than it is?

author: asmi
author_rank: Super Contributor
timestamp: August 02, 2019, 12:38:50 pm
content: Quote from: djacobow on August 02, 2019, 04:05:01 amI always make my mounting holes non-conductive and pull back copper layers, so they don't transfer any heat as PCB material itself is a very bad heat conductor.Quote from: djacobow on August 02, 2019, 04:05:01 amMost of my boards are green or blue, but I did have a few black and white boards, and they turned out OK.Another thing I would suggest - once you do a cold junction compensation mod, you can calibrate thermocouples so they report more accurate temperatures. Unified Engineering FW allows setting offset and gain of each thermocouple individually, so you can tape DMM's thermocouple to device's probe and use manual bake mode to take three measurements about 30-40 degrees apart - this way you can calculate both offset and the gain.

author: NorthGuy
author_rank: Super Contributor
timestamp: August 02, 2019, 05:19:03 pm
content: If something is designed specifically for reflow, it doesn't mean that the laws of physics cease to exist in your stove.T-962 is a really bad design.Even a cheap toaster from WalMart is miles better - it has a glass to observe the process, you can put the termocouple exactly where you want it to be, you have two heaters - top and bottom, it has room so the heat is distributed more evenly, you can use an external controller so cold junction temperature is not affected by the heat of the oven. Why in the world would you trade all that for T-962?

author: asmi
author_rank: Super Contributor
timestamp: August 02, 2019, 05:57:06 pm
content: Quote from: NorthGuy on August 02, 2019, 05:19:03 pmBecause T-962 is much, Much, MUCH better than garbage Walmart toaster. But you've got to try both to know the difference.

author: lawrence11
author_rank: Frequent Contributor
timestamp: August 04, 2019, 03:39:13 am
content: Quiet both of you, my controleo3 beats you all!BTW, I need you guys help for a FPGA code, can we talk?

author: djacobow
author_rank: Super Contributor
timestamp: August 04, 2019, 09:14:39 pm
content: The controleo looks nice, but I am making progress with my T962-A, too:added the cold junction compensation (NB: cheap Amazon DS18B20 won't work in parasitic mode. They just won't. Are they countereit?)Calibrated oven by iterating through a series of setpoints, recording the reported temp from the two built-in thermocouples, plus a third thermocouple tapes to a board in the oven, then fitting a linear regression to the data to get the gain and offset settings for each thermocoupleStarted elevating the boards on a couple of these aquarium filter pellets (https://www.amazon.com/gp/product/B001CZXZEU)I ran 6 boards today and they all came out looking pretty good and working to boot!I think I will try to tweak my custom profile to maybe reduce the time at 250. A few of the parts with white plastic (buttons) are slightly discolored. I also will probably open the oven up one more time to replace the super whiny fan with a quieter one.Overall, though, I'm almost pleased.