Homebrew PCBs

I did a bga sot-70ish  type 6 pin, After several failed attempts, I left the etch resist on, which acted like a very thin soldermask and it did indeed work, but it was ugly and stinky as the mask was burnt. I've decided to stay away from bga, just so I can visually see the connections. 
I use a black and Decker convection with two elements on top and bottom (4 total) I do 6X9 boards with mostly sot-23 and so and sop sized ic. I manually control it by setting it full on (not broil), watching my temp gauge and opening the door slightly to hold a temp. I try to follow the profile listed on Kesters site for the paste I use, and have not had a failure yet.  I do not use the ez-bake method of running a line of paste, but prefer to apply a small bead per pad. Takes longer but no shorting or rework required. 
JT

  ----- Original Message ----- 
  From: javaguy11111 
  To: Homebrew_PCBs@yahoogroups.com 
  Sent: Sunday, June 20, 2004 1:01 PM
  Subject: [Homebrew_PCBs] Reflow Oven (was Re: 4 Layer)


  --- In Homebrew_PCBs@yahoogroups.com, "Phil" <phil1960us@y...> wrote:
  > I'm in the process of looking for a toaster oven to turn into a 
  > reflow oven.  I've been looking in second-hand stores and most of 
  > these are pretty junky.  I saw a convection toaster oven for like
  $70 
  > new at (I think) target.  Given that these essentially blow hot
  air, 
  > I thought it might be ideal for conversion and that it might be a 
  > solution to the heat loss problem.  I think I'd need to install
  some 
  > sort of flow defuser to prevent moving of smaller, lighter parts.  
  > Has anyone tried one?  
  > 
  > I might want to build a controller for it that would cycle the heat 
  > (pre-heat, heat, cool down) in a controllen fashion.
  > 
  > --- In Homebrew_PCBs@yahoogroups.com, Markus Zingg <m.zingg@n...> 
  > wrote:
  > > 
  > > I do have one of them here to play with, but I heard that the heat
  > > disapears way too fast if you have to open the door to feed it. 
  > Since
  > > I intend to solder BGA's with it I figure I will have to modify it
  > > quite a bit. Did not yet found the time to start this project,
  but 
  > the
  > > day will come - I'm sure.
  > > 
  > > Markus


  --- In Homebrew_PCBs@yahoogroups.com, Markus Zingg <m.zingg@n...>
  wrote:
  > >One of these days I will do multilayer. Biggest problem is having a
  > >place to setup a PTH station. It will be a while before I have a
  place
  > >where I can do something like that. 
  > >I do not use a "real" reflow oven, but my cheap little toaster oven
  > >does a pretty good job of pretending to be one.:)
  > 
  > I do have one of them here to play with, but I heard that the heat
  > disapears way too fast if you have to open the door to feed it.
  Since
  > I intend to solder BGA's with it I figure I will have to modify it
  > quite a bit. Did not yet found the time to start this project, but
  the
  > day will come - I'm sure.
  > 
  > Markus

  The process with my oven is to start cold. I put the board in, close
  the door and turn the heat up to about 250F. I wait about two minutes
  to provide a little of preheat time. I then turn the oven up to max
  and in about 2 to 2 1/2 minutes the solder is melted. I then turn off
  the oven, open the door and wait about 5 minutes for cooldown. 

  I have not lost a board or a component yet, but there a few things to
  keep in mind. Any tall components, like connectors, will cast a shadow
  and slow down the reflow of the shaded components. So I leave things
  like large connectors off. My oven has one heating element on top and
  one on the bottom. So there is definitely uneven heating. The largest
  board I have done so far is 2.5 by 3 inches. Based on how the relfow
  went on that one, I think that is about the limit for this oven.  

  My next board will probably be in the 3x5in size and for that one I
  will invest in a convection oven to get more even heating.

  I have attempted one BGA component which was an 8 pin 555 timer. The
  problem I had was not with the oven, but the lack of a solder mask. So
  the solder wicked along the traces and the component did not set
  right. When I figure out what solder masking method I want to use, I
  will give the BGA's a try again. 



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