Homemade PCB baking board

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Hello everyone,

Some background. I have been doing homemade through hole PCB for awhile now. I used the toner transfer method with an iron and have recently upgraded to the laminator. I am not transitioning to the surface mount designs at home. I am running into an odd phenomenon that I haven’t been able to find a resolution to. I have an idea what the cause is but I just wanted to run it by someone else for verification and possible resolutions.

The issue is that when I am doing the reflow in the toaster oven the board cooks (turns brown). This is a cosmetic issue but it also a performance issue because the cooking also makes the board adhesive bubble underneath the copper. I am suspecting the problem is the oven because of how it is heated. I am using a black and decker toaster over. It has warm, bake, broil, and toast settings. I have tried bake, broil, and toast with the same results. I suspect the issue is from the direct heat of the toaster over and the heating element locations. It is doing more of a direct heating rather then a convection heating but at the same time I have read many posts about the same setup as me with no issues.

My heat cycle is to turn the oven on and let it hit 85C before I turn it off for two minutes. This allows it to ramp up to 125C and flatten out. I turn the oven back on and watch for reflow (with my solder paste that appears to be around 165C, when the paste is shiny). I let the paste be shiny for maybe 30 seconds and shut the oven off. I then let it soak for about 15 seconds and open the door for cooling off.

So any ideas on my board baking problem or any improvements to the process?

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Are your board G10 (epoxy-glass) or another material?

If the pcb is discoloring then it is getting too hot. Sound like you need better temperature control.

There is a toaster oven reflow project here on SparkFun. Read up on it and see if these issue has been addressed.

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Ya, sounds like by the time you see the solder reflowing, the temp at that particular point in the solder might be X, but the temp around it that still waiting to soak in is X+100 (or whatever the number might be), causing overshoot, and causing it to burn the PCBs.

Short of using the suggestion above and using a proper controller, if it was me, I’d try shutting the heat off as soon as you see ANY solder reflowing at all, then cracking the door open a bit after you see that last bit of solder reflow.

Are you using the little dial on the front as an indication of actual temperature? That’s no good. Those aren’t any sort of accurate by any stretch of the imagination.