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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