Homemade PCB baking board

Discussion in 'The Projects Forum' started by cl10Greg, Mar 20, 2014.

  1. cl10Greg

    Thread Starter Active Member

    Jan 28, 2010
    49
    0
    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?
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,769
    969
    reflowing through hole? or are these boards you are reflowing SMT boards you purchased from a proper board house?

    Where is your thermocouple placed?
    Where are the heating elements?
    Toaster model #

    Have you tried using a cookie sheet under the board if the burning is from the bottom?
    You simple need to shield the boards from the direct heat.
     
  3. Markd77

    Senior Member

    Sep 7, 2009
    2,803
    594
    Maybe a bit more airflow would help, you could drill a small hole and make or find a metal fan for the inside and put a small motor on the outside.
     
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
    5,984
    3,725

    You need to add a thermocouple and a control circuit to control temp. You can't just act like Casey Jones at the valve. The size (mass) of your temp sensor also impacts the time constant of your control loop. Small temp sensors are best.
     
  5. burger2227

    Member

    Feb 3, 2014
    190
    24
    Is your toaster oven a B & D by any chance? Does it have a windup timer that goes ding?

    Set it to broil and it will only heat up one element. Set it to a temperature and it will act like an oven, Set it to toast and toast you will get with both elements going full blast.
     
  6. OldSkoolEffects

    Member

    Nov 18, 2009
    68
    1
    Ben Heck on YouTube has a couple of videos on using a toaster oven to reflow, and how to add the capability to ramp one witha few simple mods.
     
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