Cheap reflow soldering with cooktop - Page 1
Forum section: electronics / projects

author: frenky
author_rank: Unknown
timestamp: October 10, 2017, 12:13:17 pm
content: I have decided to build a simple reflow soldering statin for as little $$$ as possible.This will be a build log showing my progress.Ingredients:Electric cooktop (15€)K-Type thermocouple with MAX6675 (2€)Remote Controlled Power Switch (10€)TCST2000 optoisolator (1€)http://www.vishay.com/docs/83762/83762.pdfArduino nano clone (2€)Aluminium plate (1€)

author: tggzzz
author_rank: Super Contributor
timestamp: October 10, 2017, 12:16:25 pm
content: You may or may not learn anything from my experiences athttps://entertaininghacks.wordpress.com/2015/03/25/assembling-pcbs-with-surface-mount-components/

author: Jeroen3
author_rank: Super Contributor
timestamp: October 10, 2017, 12:23:00 pm
content: Not to spoil your plan, but you can buythese.(its an ebay link, so it wille expire, search for "pid controller")

author: frenky
author_rank: Unknown
timestamp: October 10, 2017, 12:33:48 pm
content: Thank you. I'll check it out.So the idea is simple...Put alu plate on the cooktop (to get uniform temperature) and use arduino to regulate temperature by switching cooktop on and off.And I'll try to follow this optimised temerature reflow profile:http://www.nortec.co.il/image/users/82719/ftp/my_files/int/optimizing_reflow_profile_via_defect_mechanisms_analysis.pdf?id=3723713I have already opened the remote switch plug and I'm 99% sure that I know how to turn it on and off without remote signal.Sketch:

author: frenky
author_rank: Unknown
timestamp: October 10, 2017, 12:40:01 pm
content: Quote from: Jeroen3 on October 10, 2017, 12:23:00 pmHuh.That is cheap...Well I'll still continue with my version because it will be able to follow strict time/temp profile.

author: rstofer
author_rank: Super Contributor
timestamp: October 10, 2017, 12:53:01 pm
content: I just put the PCB on top of the hot plate and turn it fully on. When the solder flows, I remove the board - carefully - and then turn off the hot plate.My PCBs are small so there is no need for a heat spreader.I also have a converted toaster oven for more complex projects but the hotplate works well.

author: frenky
author_rank: Unknown
timestamp: October 11, 2017, 05:32:07 am
content: I did a bit of testing yesterday....First I've put alu plate on cooktop and measure the rate of max temp increase on top of it:Then I removed alu plate and just placed small pcb on top of cooktop:Conclusion...Alu plate is a bit too big to allow for fast enough temperature climb (from 187*C to 220*C).Cooling of alu plate and cooktop is way too slow. So after temp reaches 220*C I'll have to quickly remove pcb and put it on big alu heat sink to reach 4*C/sec cooling.

author: hermit
author_rank: Frequent Contributor
timestamp: October 11, 2017, 09:25:14 am
content: Quote from: Jeroen3 on October 10, 2017, 12:23:00 pmI had a friend, retired EE, use these for a brew rig. He finally gave up and went with an Arduino because he couldn't get the control he wanted from it. He designed, built and did the software for industrial control systems for a major manufacture so it wasn't his shortcomings in knowing how to use the hardware. When mashing for beer you have to keep the temp very stable within a degree or two of target. Moving the temp on a mass of 7+ gallons isn't that easy with 120VAC heater so this PID must not have been that sensitive. In the end he just adjusted the pulse width down as it approached temp instead of doing a simple on off around the target temp.

author: frenky
author_rank: Unknown
timestamp: October 11, 2017, 07:21:47 pm
content: Today I tested if I can turn on and off the remote Power Switch trough optocoupler.I have found a pin on IC which is connected to transistor that turns relay on and off.Then I've cut the trace and soldered wires from 5V line and resistor on transistor base.This two wires are connected to the detector part of optocoupler TCST2000 (just because I had it at home).IR diode in TCST2000 is connected to arduino 5V trough 470 ohm resistor.Like this:And it works.

author: frenky
author_rank: Unknown
timestamp: November 10, 2017, 06:50:51 am
content: So the big cooking plate was cooling down way to slow so I went searching for alternatives.I have bought a small round 30mm ceramic heater:https://www.ebay.co.uk/itm/121691295611It is big enough for my neeeds and small enough that it does not have a big thermal mass so it cools down really fast.I've sandwiched K-type thermocouple between this heater and another one which is just for holding it in place.Then I connected the heater to 12V/2A and measured temperature rising in the "sandwich" and on top of pcb. My setup:And the chart (blue is inner probe and red is probe on top):Solder paste is Sn62/Pb36/Ag2 and it melts at 179*C.When paste started to melt the temperature in sendwich was 140*C and on top of pcb 149*C.My guess is that thermocuples are not precise enough or did not have good contact?Anyway I'll use inner 140*C temp as my reference for 179*C at solder paste level.Next I'll make a simple temperature regulation and start using it for reflow.

author: capt bullshot
author_rank: Super Contributor
timestamp: November 10, 2017, 12:15:31 pm
content: Check out thishttp://www.ganssle.com/tem/tem338.htmlscroll down to Tools and Tips section

author: frenky
author_rank: Unknown
timestamp: November 10, 2017, 12:31:37 pm
content: Nice. It is similar to using cooktop which was working just fine for me.I have switched to a small ceramic heater because it cools down faster and it uses a lot less space.And I would like to follow reflow curve as close as possible because I'll be selling this modules.

author: ebclr
author_rank: Super Contributor
timestamp: November 10, 2017, 12:50:09 pm
content: This controller is even better because you can draw the reflow steps with 10 segmentshttp://www.altec.cc/downloadfile/pc900_en.pdfhttps://pt.aliexpress.com/item/PC410-Temperature-Controller-Panel-For-BGA-Rework-Station-with-RS232-Communication-Module/32805668263.html?spm=a2g03.search0204.3.2.vUaH9f&s=p&ws_ab_test=searchweb0_0%2Csearchweb201602_1_10152_10065_10151_10068_10344_10345_10547_10342_10343_10340_10341_10548_10541_10307_10060_10155_10154_10056_10055_10539_10537_10536_10059_10534_10533_100031_10103_10102_5670011_10142_10107_10173_5660011_10562_5740011_10084_10563_10083_10561_10566_10564_10565_10312_10313_10314_10550_10073_10551_10552_10553_10554_10557_5650011%2Csearchweb201603_4%2CppcSwitch_5_ppcChannel&btsid=1eb01be1-774e-47f5-9e78-dff6cf7df3e4

author: phil from seattle
author_rank: Super Contributor
timestamp: November 11, 2017, 05:50:35 pm
content: For cool down, why don't you hook up a small fan? I would think you could PID it for the right cool down profile. Though I'd bet you could find a single setting that would approximate a reasonable profile.On a less supportive note, I've seen lots of reports of successful reflow just using a cheap skillet on a hot plate. No control at all. I love the idea of building a precise profile controlled reflow oven but sometimes low-tech beats high.