What type of toaster oven would be good for reflow? - Page 1
Forum section: electronics / general

author: alank2
author_rank: Super Contributor
timestamp: September 15, 2013, 12:00:54 am
content: Hi,I live in the US so most are going to be 110/120V. I'm not sure the type of heating power that is necessary. Is a convection one a better one?Thanks,Alan

author: nanofrog
author_rank: Super Contributor
timestamp: September 15, 2013, 02:54:17 am
content: Convection is the better way to go. A lot of the commercial stuff is convection, even the benchtop units are moving to this (IR convection), such as the Manncorp 850.Might want/need to insulate it, as the larger ovens tend to have a problem getting to/retaining the higher temp range in the cycle from what I've read on converted units. Not sure about turbulence (air flow high enough to blow parts off the board) of a toaster sized unit, but would probably be OK.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 15, 2013, 09:56:42 am
content: You ideally want heaters top & bottom, a nice big clear window and a tray that doesn't bump when opening & closing. Minimum power about 1-1.5kw (before power control )You want a good proportion of the heat to be by convection to avoid scorching - I run mine at just below glowing.I've not tried fan convection ovens but they seem like a good idea.Don't bother with building PID controllers etc. Once you get the power setting right, just turn on, wait for reflow then open the door.And obviously stay away from leadfree

author: Psi
author_rank: Super Contributor
timestamp: September 15, 2013, 10:14:06 am
content: Fan ovens will blow/move the parts on your board if you're not careful about adjusting the fan speed.I tried a video card reflow in a fan oven and had to re-attach a couple of components.

author: Legit-Design
author_rank: Frequent Contributor
timestamp: September 15, 2013, 10:39:12 am
content: Saw this one project, which stated that running fan will dissipate the heat into housing much faster, so it needs better insulation or more power. Or just not running the fan.

author: nanofrog
author_rank: Super Contributor
timestamp: September 15, 2013, 11:53:57 am
content: Quote from: Psi on September 15, 2013, 10:14:06 amGood to know.Do you recall the size of the parts that were blown off?

author: AlfBaz
author_rank: Super Contributor
timestamp: September 15, 2013, 02:33:38 pm
content: Quote from: Psi on September 15, 2013, 10:14:06 amThe first time I ever tried that I took the board out straight away, being worried about the heat... heaps of components slid off

author: marshallh
author_rank: Unknown
timestamp: September 15, 2013, 03:33:44 pm
content: Just did a board yesterday. It's a convection oven with 4 elements. Exhaust fan kicks on at the knee of the profile. You'd need a pretty strong fan to cause a problem.

author: alank2
author_rank: Super Contributor
timestamp: September 15, 2013, 08:02:52 pm
content: I went to look at them. Some have metal type heater rods and others have what looks like a glass tube (is this a quartz heating element?). Which is better?Thanks,Alan

author: Kjelt
author_rank: Super Contributor
timestamp: September 15, 2013, 08:16:38 pm
content: My $2k reflow oven (but that's not what I paid for it 2nd hand) uses quartz elements and with it's PID and a digital temperature sensor I could get almost a perfect reflow graph. So the quartz elements are fast enough to do the trick. My oven only has upper quartz elements mounted. You only reflow one side at a time or you have to use glue.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 15, 2013, 09:15:11 pm
content: Quote from: alank2 on September 15, 2013, 08:02:52 pmprobably not much difference - quartz may put out more IR, but may also heat up quicker.

author: alank2
author_rank: Super Contributor
timestamp: September 16, 2013, 12:22:24 pm
content: I picked up a black and decker model for $40. It has a pair of quartz elements on the top and also on the bottom. I guess each one is probably 700W, so both together 1400W. There is a convection fan as well, but it doesn't seem to push too much air so I doubt any components getting blown will be an issue.I'll try and mess with the controls and see how close I can get to a leaded reflow profile manually, but I really want to build a PID controller for it as a learning project. I've been doing some PID stuff and I won't mind testing what I've learned to see if it will work.Here are a few questions I have:1. What makes a SSR get hot? Switching speed or simply the current going through it?2. For 12.5A @ 120VAC, how large a SSR should I get? 25A? 40A?3. When you read about reflow profiles - are they talking about the air temperature around the board, or what the board goes through itself? Should I mount a sensor on a board or in the outgoing air stream from the convection fan?4. I've read that some people will insulate the oven more. Does this involve the area between the interior metal shell and the outer metal cover? Someone mentioned fiberglass for this, can it take the heat without damage or burning?Thanks,Alan

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 16, 2013, 12:54:33 pm
content: Quote from: alank2 on September 16, 2013, 12:22:24 pmThe latter.For minimum noise, use a zero-crossing type - for heating you can switch on/off for whole numbers of mains cyclesQuoteSome headroom is always good - 25A should be more then adequate. may need a small amount of heatsinkingQuotethe boardQuoteMay allow less power to be used, but possibly mpre throuble than it's worth

author: alank2
author_rank: Super Contributor
timestamp: September 16, 2013, 01:01:30 pm
content: Thanks for the answers Mike - do you have any tips for how to mount a temp sensor to the pcb? Just position it so it sits on top of the board? Use a mini clip of some sort to press the sensor against the pcb?

author: Psi
author_rank: Super Contributor
timestamp: September 16, 2013, 01:10:58 pm
content: Quote from: nanofrog on September 15, 2013, 11:53:57 amThey weren't blown off the pcb so much as slid off the pads a bit1 or 2 0603 caps, a 100uf electro cap and one of the power inductors.Was easy fixedI opened the oven door and let the pcb cool down before removing it so i know it was the fan that caused it and not motion

author: arvidj
author_rank: Contributor
timestamp: September 16, 2013, 04:23:51 pm
content: Quote from: alank2 on September 16, 2013, 12:22:24 pmNew or used? What model?I'm also looking so I thought I'd ask.

author: alank2
author_rank: Super Contributor
timestamp: September 16, 2013, 04:48:59 pm
content: Quote from: arvidj on September 16, 2013, 04:23:51 pmIt is a Black and Decker TO1675B (Black). They make a TO1675W for white too. I got it new at Walmart in the US. I had it apart last night and it is easily hackable from what I can see.Good luck,Alan

author: Kjelt
author_rank: Super Contributor
timestamp: September 16, 2013, 05:58:13 pm
content: Use a thermocouple and take a prototype pcb with holes to mount the wire of the sensor against the board.Then you will notice that the temperature and the profile will be different on different locations of your oven (directly under the quartz hotter).Store the temperature measurements and compare with the desired graph and adjust the PID.I found out (in my oven could be totally different from yours) that the PID should be quite fast responding since the quartz have already a delay of a few seconds. To reach the first phase of around 160 degrees C, I could continu to give power then it should stay there for awhile (periodically power on/off) then fire all the way up to just for the endtemperature and then stop. If end temp reached cool a.s.a.p. by venting or opening the tray.It is not very precise, you can get away with quite some fluctuation or deviation and still have good results.

author: nanofrog
author_rank: Super Contributor
timestamp: September 16, 2013, 07:33:37 pm
content: Quote from: Psi on September 16, 2013, 01:10:58 pmThanks. Good to know.

author: olsenn
author_rank: Frequent Contributor
timestamp: September 16, 2013, 07:35:05 pm
content: I wonder if a hot air gun can toast bread

author: nanofrog
author_rank: Super Contributor
timestamp: September 16, 2013, 07:46:42 pm
content: Quote from: olsenn on September 16, 2013, 07:35:05 pmSure it can. Blow torch too (handy when the power is out).

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 16, 2013, 07:56:43 pm
content: Quote from: alank2 on September 16, 2013, 01:01:30 pmNope - never done it. Just heat til it flows.

author: arvidj
author_rank: Contributor
timestamp: September 16, 2013, 08:13:50 pm
content: Quote from: mikeselectricstuff on September 16, 2013, 07:56:43 pmIn my research I have found thermocouples that have an eyelet on the end. I know that Omega has themhttp://www.omega.com/pptst/WT.htmlat reasonable prices but the shipping was almost the same as the thermocouple. They are nice in that the washer on the end can use small screw sizes.I've also seen them on eBay pretty cheap with free shipping. The size of the washer on the end suggest it would be used under a spark plug to measure cylinder head temperatures.I would assume that fastening them to a scrap piece of copper clad with a brass nut, washer and screw would give repeatable results.But as others have suggested, looking in the window and watching what is actually going on seems to be a reasonable PID algorithm.Arvid

author: David_AVD
author_rank: Super Contributor
timestamp: September 16, 2013, 09:26:42 pm
content: Quote from: mikeselectricstuff on September 16, 2013, 07:56:43 pm+1 to that.Getting an oven with a good heat distribution is higher priority than a controller. The one I use has 3 elements on the top and 2 on the bottom. It's a Breville BOV800 from memory.

author: alank2
author_rank: Super Contributor
timestamp: September 17, 2013, 03:50:55 pm
content: Will this sensor work? I can drill a hole in a PCB and twist it into the surface. Will the mass of the bolt end be too much for it to change quickly enough?http://www.auberins.com/index.php?main_page=product_info&cPath=20_3&products_id=2Thanks,Alan

author: Kjelt
author_rank: Super Contributor
timestamp: September 17, 2013, 05:05:29 pm
content: The sensor should NOT have to much mass. Because this all has to heat up. You're temperature reading will be off what the board and components on the board get.Look at your components you are reflowing, 0805, 0603 don't have much mass.I use two thin wires of the two different materials you need for the right thermocouple welded together, nothing else. Looks something like this:

author: poorchava
author_rank: Super Contributor
timestamp: September 18, 2013, 07:54:49 am
content: I have some jellybean 800W toaster owen (Optimum brand). It has 2 heaters and I had to mask the heating elements, because radiation was heating the pcb to much higher temperature than the air was at.

author: alank2
author_rank: Super Contributor
timestamp: September 18, 2013, 12:13:42 pm
content: Hi Everyone,I ordered a zero crossing SSR and some thermocouples to play around with it. Assuming 60 cycles, will a zero crossing SSR be capable of switching on and off at every cross (120 per second) so if I use a 1s frequency for my PWM does that give me the option to have 0-120 (fully off to fully on) for my control output?I've recently gotten USB to work on AVR's so I'm going to make a PC side application that runs the PID algorithm, knows the reflow profile, and graphs both the profile and actual temperature on a notebook. The AVR side will be very simple. It will comm with the PC over USB and will provide the temperature from a max6675 and run the PWM for the SSR based on what the PC side application tells it to do.Thanks,Alan

author: alank2
author_rank: Super Contributor
timestamp: September 29, 2013, 01:31:49 pm
content: Hi,I thought I'd post an update on how my PID reflow oven is going. I finished up the oven wiring and finally got the SSR box built. I chose to put the SSR's in a separate box so they won't get hot with the oven. My AVR is an ATMEGA32U2 and it outputs a PWM for the heating ssr and sends out a signal to turn the fan ssr on or off as well. It communicates with the PC over USB. So, it in the end will be a 4 component project - oven, ssr box, tiny avr control board, and finally a notebook PC.My PC application will eventually have a nice graph and nice controls, but right now it is functional:It has a reflow profile that allows to to verify that the pcb's are kept in their appropriate zone for a specific number of seconds and also that a specific ramp rate is not exceeded:Code:Each stage in a profile will have:Name"Warm up"Setpoint150 Deg CMax Change Rate3 Deg C(0 is disabled which is an immediate set point change)Timer120 secTrigger0 is begin timer immediately, 1 is begin timer when pv>=threshold, 2 is begin timer when pv<=thresholdTrigger Threshold100 Deg CFanOn/Off"Standard Lead Profile",25,10,225,50(profile name,default setpoint,graph horizontal, graph vertical max, graph vertical separations)"Warmup",150,3,90,1,100,On<- move to 150 C at 3 C per second, begin timer when PV>=100 so it will be between 100 and 150 for 90 seconds"Reflow",200,3,90,1,185,On<- move to 200 C at 3 C per second, begin timer when PV>=185 so it will be between 185 and 200 for 90 seconds"Cool",25,6,1,2,50,On<- move to 25 at 6 per second, stage will not end until 1 second at 50 C (light will go out when boards can be touched!)Here is the tuned PID algorithm locking on to 150 deg C:Here is my sample reflow profile. 90 seconds in the 100-150 range for warmup/flux activation and 90 seconds in the 185-200 range for reflow and finally a cool down that doesn't exceed 6C/s (like my oven can cool that fast anyway!)I've still got a lot of work to do, but I'm pretty pleased tonight that I was able to get the PID parameters tuned.Thanks,Alan

author: Zsola
author_rank: Newbie
timestamp: October 12, 2013, 09:18:01 pm
content: Quote from: David_AVD on September 16, 2013, 09:26:42 pmFor reballing the heat resistant foil, the kapton tape is used (you can check digikey or else to get), so you can fix the thermocouple on the PCB with that. Use a wider tape, narrow (less than 1 cm) ones can peel off easily. If you have to measure the exact temperature of a larger part, you can use thermal silicon grease too. Eg. on a bigger CPU with heat spreader.