What type of toaster oven would be good for reflow?

[alank2]

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

[nanofrog]

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.

[mikeselectricstuff]

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

[Psi]

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.

[Legit-Design]

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.

[nanofrog]

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.

Good to know.

Do you recall the size of the parts that were blown off?

[AlfBaz]

I tried a video card reflow in a fan oven and had to re-attach a couple of components.

The first time I ever tried that I took the board out straight away, being worried about the heat... heaps of components slid off

[marshallh]

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.

[alank2]

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

[Kjelt]

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.

[mikeselectricstuff]

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

probably not much difference - quartz may put out more IR, but may also heat up quicker.
 

[alank2]

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

[mikeselectricstuff]

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?

The latter.
For minimum noise, use a zero-crossing type - for heating you can switch on/off for whole numbers of mains cycles

2.  For 12.5A @ 120VAC, how large a SSR should I get?  25A?  40A?

Some headroom is always good - 25A should be more then adequate. may need a small amount of heatsinking

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?

the board

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?

May allow less power to be used, but possibly mpre throuble than it's worth

[alank2]

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?

[Psi]

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.

Good to know.

Do you recall the size of the parts that were blown off?

They weren't blown off the pcb so much as slid off the pads a bit
1 or 2  0603 caps, a 100uf electro cap and one of the power inductors.
Was easy fixed

I 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

[arvidj]

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. ...

Alan

New or used? What model?

I'm also looking so I thought I'd ask.

[alank2]

New or used? What model?

It 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

[Kjelt]

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.

[nanofrog]

They weren't blown off the pcb so much as slid off the pads a bit
1 or 2  0603 caps, a 100uf electro cap and one of the power inductors.
Was easy fixed

I 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

Thanks. Good to know. 

[olsenn]

I wonder if a hot air gun can toast bread

[nanofrog]

I wonder if a hot air gun can toast bread

Sure it can. Blow torch too (handy when the power is out). 

[mikeselectricstuff]

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?

Nope - never done it. Just heat til it flows.

[arvidj]

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?

Nope - never done it. Just heat til it flows.

In my research I have found thermocouples that have an eyelet on the end. I know that Omega has them http://www.omega.com/pptst/WT.html at 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
 

[David_AVD]

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?

Nope - never done it. Just heat til it flows.

+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.

[alank2]

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=2

Thanks,

Alan