Manual (dumb) toaster-oven reflow parts recommendations? - Page 1
Forum section: electronics / beginners

author: RL_Tracksuit_Electro
author_rank: Contributor
timestamp: January 19, 2020, 05:52:37 pm
content: I want to do very low volume hobby smd reflow, been doing with hot air station and want to try oven.I want to dip my toe in the water with the "watch it through the glass & thermocouple" approach, i.e. no microcontroller running a profile.Basically, all I'm willing to invest in now is:1. cheap toaster oven2. multimeter with thermocouple I'll just wedge in through gap in the door mounted to a bare pcb or something with capton tape.If you're doing it this way (or used to), would appreciate the amazon links to toaster oven & meter/couple you're using. Trying to avoid guessing and finding e.g. the door has no gap to run in a couple wire, etc. Otherwise I'll just guess. Really looking to keep this under $50 US. Thanks.

author: jmelson
author_rank: Super Contributor
timestamp: January 19, 2020, 06:03:46 pm
content: Quote from: RL_Tracksuit_Electro on January 19, 2020, 05:52:37 pmI use a cheap (WalMart) GE brand toaster oven with 4 heating elements. These are straight rods about 1/4" diameter that run horizontally, left to right. Two above and two below the rack. It has a thermostat that is outside the chamber, and so must work by self-heating due to the current.I bought a ramp and soak thermocouple controller, that allows a thermal profile to be entered -- heat to 180 C, hold for 1 minute, heat to 245 C, hold for 1 minute, cool to ambient in 2 minutes. I lucked into a lifetime supply of micro-size thermocouple extension wire. I poke the thermocouple into aplated-through hole in the PC board, thus the controller is monitoring the true temperature of the board.I have done over 2000 boards with this setup, and it works great. Don't forget to put the thermocouple in the hole in the board, or the boards willgo up in smoke. Apparently, the PC board material and the ICs are great IR absorbers, and the thermocouple just hanging in the air is NOT!I made that mistake ONCE, only.I can do 4, 6 or 8 boards at one time, depending on size.Jon

author: Peabody
author_rank: Super Contributor
timestamp: January 19, 2020, 06:20:03 pm
content: An alternative you might want to consider is a hot plate. I did a hot plate project which consists of the $10 Walmart hot plate, a $5 circular saw blade, and three screws, total cost about $20. Instead of measuring temperature with a thermocouple, you simply turn it on for a certain period, then off for another period, then back on for the last period, and it's the same for pretty much any board size. So instead of a thermocouple and its mounting issues, you just need a watch, or a previoudly-recorded audio tape that tells you when to turn it on and off.There's a related video and a Github repo:https://github.com/gbhug5a/Reflow-Hot-Plate-and-ControllerI donated mine to my local maker space, and they report it works fine. Leaded solder paste, of course. When I was testing it, I found it to be very forgiving, with no scorching of anything.

author: rstofer
author_rank: Super Contributor
timestamp: January 19, 2020, 06:24:27 pm
content: For small boards, I use a hot plate. I put the board on the plate, turn the knob fully on and watch for the solder to flow. I remove the board with tweezers, trying hard not to dislodge any parts, and set it aside to cool. Then I turn off the hotplate.Toaster oven: Mine is automated so no help there. I did fill the cavity between the inner and outer wall with high temperature matting (McMaster-Carr) because the heat loss was so high I really couldn't get up to temperature anywhere near fast enough.If you think you can see the solder flow, manual control may be enough. The thing is, I don't think you will be able to see the solder everywhere on the board.

author: RL_Tracksuit_Electro
author_rank: Contributor
timestamp: January 19, 2020, 06:46:25 pm
content: Thanks for the tip, I want to try this but you seem to imply leaded paste is necessary...I have lead free but advertised as "low temp", the tube says melting point 137C/278F.https://www.amazon.com/gp/product/B017RSGPI8/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1Is there something special about the leaded paste or did you just mean shorthand for melting point?Any idea if the paste I have is within the range the hotplate approach can do?

author: jesuscf
author_rank: Frequent Contributor
timestamp: January 19, 2020, 07:02:30 pm
content: Any cheap multimeter with temperature reading up to 250C should do; they sell for about 30$. A quick search in Amazon gives too many candidates to list here. One option you must be careful with is the type of thermocouple wire that comes with the multimeter. The thermocouple wire must be rated for temperatures over 250C. You need to look for a thermocouple probe with fiber glass or metal shielding/insulation. The ones with the yellow or blue plastic shielding are rated only for low temperatures and will quickly melt in the toaster oven. The ones with white shielding with blue stripes are fiberglass insulated and are usually rated for up to 700C but some are rated for only 200C.An even cheaper solution will be to buy a digital thermometer like the TM902C and a separate k-type thermocouple rated for the correct temperature. This combination should be around 15$.

author: Kasper
author_rank: Frequent Contributor
timestamp: January 19, 2020, 10:10:09 pm
content: If you are just making stuff for yourself and you don't mind a bit of risk, you don't really need anything other than a toaster oven.That is all I used in 2 different workplaces, a lab in university and in my backyard.I worry a bit about reliability but I've never had a problem and I always get good looking joints.At home I use an IR toaster oven I bought used from a local classified ad for $20.Have used it with leaded and lead free solder paste with no problems.Rarely use it so haven't bothered with any fancy controls or even a temperature sensor. I just change the temperature setting manually once a minute or two following a table I wrote based off reflow profile for the solder. I'd share the table but its handwritten on paper I left in the oven that is in storage now.

author: Peabody
author_rank: Super Contributor
timestamp: January 20, 2020, 02:58:14 am
content: Quote from: RL_Tracksuit_Electro on January 19, 2020, 06:46:25 pmIt was shorthand for the melting point. For leaded solder that's 183°C, which is a lot higher than your low-temp paste. So the hot plate would certainly be hot enough. You would probably want to cut back on the "on" time periods. I don't know if low-temp paste is any good.

author: RL_Tracksuit_Electro
author_rank: Contributor
timestamp: January 20, 2020, 03:49:25 am
content: Thanks. Went to Walmart today and got that exact hotplate and a table saw blade, some screws from Home Depot, all under $20. Will give it a try later in the week.

author: Peabody
author_rank: Super Contributor
timestamp: January 20, 2020, 02:58:04 pm
content: I don't remember if I included this advice in the repo, but be sure to remove the printing and any coating from the saw blade before you heat it up. I think I used acetone, but paint thinner or charcoal lighter, or maybe even alcohol, might also work. And even then, fire up the whole setup outside for about 5 minutes to burn off anything that might stink up your house.I read through some of the negative reviews on the low-temp paste, and I have my doubts about how good it is. It just seems if it was all that good it would be in wide use, and I don't think that's the case. A good leaded paste behaves very predictably, and I think is the one to use for anything except commercial products. The problem with any paste is that they have a limited lifespan, even if kept refrigerated. I don't know what the solution is for that.And finally, what I've found is that even with a syringe it's almost impossible to keep from putting too much paste on. So if you can use a stencil, that will really help.Good luck.

author: jmelson
author_rank: Super Contributor
timestamp: January 20, 2020, 05:40:40 pm
content: Quote from: RL_Tracksuit_Electro on January 19, 2020, 06:46:25 pmNope, I use mostly lead-free solder. Some work well, some don't. I have found GC10 to be simply amazing, and now even use it where leaded solder could be used, as it works so well. You do have to get just a little hotter for the lead-free to reflow. I peak at 235 C to 245 C depending on the boardwith the GC10 paste.Jon

author: jmelson
author_rank: Super Contributor
timestamp: January 20, 2020, 05:42:51 pm
content: Quote from: RL_Tracksuit_Electro on January 19, 2020, 06:46:25 pmI tried some of this with a temperature-sensitive component, it was horrible. It was so brittle that a mere touch with a fingernail would flick thepart off the board.Jon

author: jmelson
author_rank: Super Contributor
timestamp: January 20, 2020, 05:46:53 pm
content: Quote from: Peabody on January 20, 2020, 02:58:04 pmYES, paste application is the SECRET to reflow! I have to reduce the size of the stencil apertures smaller than the pads, and the smaller thelead pitch, the more the apertures need to be reduced. Then, I use a 3 mil brass stencil (~0.075 mm) to keep the paste volume down. SOIC parts are really forgiving, but anything smaller, like SSOP or QFP parts are likely to form bridges with too much solder.Jon

author: RL_Tracksuit_Electro
author_rank: Contributor
timestamp: January 21, 2020, 02:13:45 am
content: Quote from: Peabody on January 20, 2020, 02:58:14 amI have only done about 100 joints with the stuff I linked to, but with the hot air station I've been satisfied with the results with this solder, and even did some very tight pitches I was nervous about. Once I learned the right airflow, distance, etc. (the right "touch") seems fine. Just tedious.I'm hoping the hotplate approach will make it easier, we'll see how it goes as opposed to the hot air approach.

author: Peabody
author_rank: Super Contributor
timestamp: January 21, 2020, 06:49:55 pm
content: If you're going to use the low-temp paste, then I think you may need to recalibrate my On times. Basically, the solder should not melt during the soak phase, and actually should not melt until just after the second On stage has shut down - the temperature will still be increasing at that point (see my graph in the repo). And for each test, you have to start with everything at room temperature.I don't think you have to do the tests using SMD parts. I think you can just put a few small blobs of solder on an old piece of PC board, and see when they reflow. They would reflow at about the same time if a part was present - maybe just a hair later. Anyway, if the low-temp stuff works, you'll have plenty of leeway on temperature without damaging any parts.