Are there any advantages to skillet reflowing vs toaster oven reflowing... - Page 1
Forum section: electronics / projects

author: alank2
author_rank: Super Contributor
timestamp: April 17, 2015, 12:22:07 pm
content: Are there any advantages to skillet reflowing vs toaster oven reflowing?I've reflowed in a toaster oven a few times now and I keep reading about people using a skillet for the job. I've got a pid controller so I'm thinking, I could control the heat going to a skillet just as well as the oven. One thing might be that positioning the temperature sensor (j or k type wire twisted end) might be easier because I don't have to close the door and try to get it to stay where I put it. Also, you can see what is going on directly from the top down and can try to tweak anything that goes wrong.Does anyone prefer skillet to oven or oven to skillet and if so, why?Do you have to do anything special to get even heat in the skillet?

author: tggzzz
author_rank: Super Contributor
timestamp: April 17, 2015, 12:47:34 pm
content: I have an oven available at Bristol Hackspace, but haven't felt the need to use it - yet. I've documented my experiences of using a pan on a gas ringhttps://entertaininghacks.wordpress.com/2015/03/25/assembling-pcbs-with-surface-mount-components/. PID? Bah, humbug, that's for sissiesJust use a non-contact hand-held thermometer, and watch - as soon as the solder flows, lift the PCB out.One thing thatwouldmake me seriously consider using the oven is if I wanted to mount components on both sides.

author: Pjotr
author_rank: Frequent Contributor
timestamp: April 17, 2015, 01:35:50 pm
content: I am using a bare aluminium plate of 15 cm x 15 cm and 20 mm thick. Heat it up slowly on gas stove (but an electric should work also fine) until all the solder melts. Works perfect. A thick alu plate has a good even heat distribution.When I have large components on the board, I put a small oven resistant glass baking dish over the board to keep the heat as much as possible at the board.

author: cjk2
author_rank: Contributor
timestamp: April 17, 2015, 03:56:30 pm
content: I use a 6 inch square, 1/4 inch thick piece of MIC-6 aluminum plate on the small size burner of my electric stove. I first set to plate on the burner, then place the board to be soldered on top. I then turn that burner to the max heat setting and wait until I see all the parts reflow. I then slide the board off the reflow plate and on to a piece of PCB material to cool down. This entire process takes about 3 minutes.The advantage of this is that you do not need a toaster and I find it easier to watch the board reflow this way.One disadvantage is that I like to hold the board flat on the plate using a screwdriver or two to make sure there is good uniform contact. The toaster would avoid this.I see no need to use fancy temperature control loops. I just heat it fast and slide it off.Edit: I should note that the 6x6x1/4 plate has about the right heat capacity to get to reflow temperature in about 2 minutes using a 2kw heat source. Thicker will take longer or require much more heat to produce the short reflow time that is desirable.

author: Pjotr
author_rank: Frequent Contributor
timestamp: April 17, 2015, 05:11:02 pm
content: SMD parts are designed to stand the process for several minutes. So doing the job too fast is not good either. You need to preheat not to fast to let the components adapt, then a phase the flux can do its work without actually melting the solder, then a heating phase to reflow the solder. It is this last phase that has to be kept as short as possible. Also too fast cooling is not advisable. A cooling faster than 2 degC/s is not recommended because the solder needs some time to form a fine grain structure.

author: alank2
author_rank: Super Contributor
timestamp: April 17, 2015, 05:14:44 pm
content: I've got the whole profile worked out and my controller does a good job, I just wonder if the skillet would have advantages that might make it better for the task. I like being able to look down on it and see what is going on, recenter a part, etc.

author: Pjotr
author_rank: Frequent Contributor
timestamp: April 17, 2015, 05:25:05 pm
content: Why would you use a skillet? Imho the bottom is too thin to get sufficient even heat spread for SMD soldering. And most are not (or stay not) flat enough. A piece of thick alu (>=10 mm) will do the job better imho.

author: alank2
author_rank: Super Contributor
timestamp: April 17, 2015, 05:29:24 pm
content: I was actually thinking of those self contained hot plates, a square one, perhaps with some aluminum on top of it...

author: Pjotr
author_rank: Frequent Contributor
timestamp: April 17, 2015, 05:49:34 pm
content: Hmmm yes, examples enough of that on YouTube and on the forum here. Seach for SMD soldering hotplate.I have some 400W 1/4" heater cartridges laying around here. When I have time I will put 4 of them directly in my alu plate and hook it to a controller. With 1600W, 1 kg alu will heat up at app. 2degC/sec, the max. recommended rate for most solder pastes. Problem is a bit to find a long enough dril. The cartridges are 6" long.

author: kjs
author_rank: Regular Contributor
timestamp: April 17, 2015, 06:30:12 pm
content: Quote from: alank2 on April 17, 2015, 05:29:24 pmGood hot plates for lab use already have a heat spreader build in (mine has copper). The one I am using has that little of a thermal mass that the controller can actually run a real profile as it's "prescribed". They are a bit pricey compared to a simple $20 "cook-top plate" but also give more repeatable results.If I have more or larger boards I know where to get them into a vapour phase machine.....

author: mazurov
author_rank: Frequent Contributor
timestamp: April 17, 2015, 09:57:07 pm
content: One advantage is that you can see what is going on. Comes in handy while soldering under a microscope, for example.

author: zapta
author_rank: Super Contributor
timestamp: April 18, 2015, 12:31:26 am
content: Another reflow method that works are those cheap eaby hot air stations.

author: tggzzz
author_rank: Super Contributor
timestamp: April 18, 2015, 08:03:39 am
content: Quote from: zapta on April 18, 2015, 12:31:26 amIf they are they kind I am thinking of, it can be difficult to ensure they don't blow devices off the board!

author: zapta
author_rank: Super Contributor
timestamp: April 18, 2015, 01:25:53 pm
content: It worked for me. When you see the solder melting you move on to another section of the boards

author: nanofrog
author_rank: Super Contributor
timestamp: April 18, 2015, 11:56:18 pm
content: Quote from: tggzzz on April 18, 2015, 08:03:39 amThen the airflow is too high.Turn it down, problem solved..

author: tonyarkles
author_rank: Regular Contributor
timestamp: April 20, 2015, 06:11:09 pm
content: I tried the skillet method this weekend because the toaster oven at the hackerspace only has a Pb profile programmed into it right now, and I only had Pb-free paste handy (and the guy who knows how to reprogram it is in Mexico...)The cheap electric skillet that I picked up had a bit of a problem: the bottom of it had serious hotspots, and the board would only melt the solder if they were on a hotspot. Not ideal. Add an aluminum plate, I figured! Unfortunately, with the plate added, the boards would only reach 175C, which wasn't quite enough to actually melt the solder!I ended up having to disassemble the "thermostat" and "calibrated" the gap in the bimetallic switch so that it would go hotter. Really that just means I grabbed it with a pair of pliers and bent it so that it was way larger. Open loop, the boards heat at around 0.5C/sec, which makes for a nice gentle profile. I'm going to have to test it out a little more this afternoon, but it looks like it'll do the trick.

author: Canobi
author_rank: Regular Contributor
timestamp: April 20, 2015, 08:44:55 pm
content: Just made a reflow hot plate recently myself. Had some assist from the engineers at work in the form of a donated heating element, and the use of a quality temp meter. The chassis is made fom an old hi if unit, the rest are parts I salvaged from the scrap metal bins. I was able to adjust the plate hight so the temp just tops the optimum melting point at the max setting (170°C melt temp in my case with a top end of 185°C).I've only done single sided boards to date so suits my needs for the moment

author: Howardlong
author_rank: Super Contributor
timestamp: April 20, 2015, 09:11:59 pm
content: Quote from: tggzzz on April 17, 2015, 12:47:34 pmAnd the same applies to an oven. I have a PID controller but it's all but useless. Why do you think they put a window in those things!?My assembler gave me a good tip a few years ago, for double sided placements put all the heavy parts on one side. The boards I do generally have no problems, the biggest on the first side are things like 16 pin TSSOP, and they stay on fine during the second reflow. Yet another thing to bear in mind when laying out a board I guess!

author: eneuro
author_rank: Super Contributor
timestamp: April 20, 2015, 10:34:58 pm
content: Quote from: Canobi on April 20, 2015, 08:44:55 pmI was thinking of something like hot plate, but... with glass casserole on top, so we have hot plate, PCB and thin layer of hot air above PCB-from hot plate catched by glass casserole like this, but reversedEverything cleary visible like... chicken cooking and easy to keep required temperature inside

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: April 20, 2015, 11:09:58 pm
content: My favoured way is a large square electric frypan, bring it up to very warm and then run the heat gun over all the parts to make sure every part is soldered.Haven't tried this with pb free though.I have to do this because my solder pasting is messy as I don't get the stencils.I have the tweezers ready if anything tombstones or doesn't align, and I only do down to 0.5mm pin pitch.

author: Pjotr
author_rank: Frequent Contributor
timestamp: April 21, 2015, 09:02:03 am
content: Quote from: eneuro on April 20, 2015, 10:34:58 pmWorks like a charmKind of a hotplate - oven combination:Quote from: Pjotr on April 17, 2015, 01:35:50 pmThe one I use is the glass lid of a 6" round small one.