Lawrence Lile wrote:

>
> I tried to explain this to my boss, who "knows not whereof he
> speaks".   I think i'll concentrate on the ability to make ONE
> prototype surface mount prototype (which we can only do very
> clumsily).  I'm going to look into the toaster oven reflow oven idea
> very seriously, maybe a dipenser for solder paste instead of a
> syringe, and a better magnyfying glass.  We could also cook up a
> solder pot for nothing, since we make things that (except for the
> fact they are intedned to cook food) would work fine.
>

Hi Lawrence,

I'm currently in the process of building a controller (Pic Based of
course) for a SMT toaster oven.  The oven needs to be  fan-forced so
as to prevent hot spots in the oven. In Australia the only one I've
found (I have searched too hard though) is imported from Italy and
costs A$200.

I been informed that the temperature profile for the toaster oven is
close enough to the recommeded profiles to work. When using a toaster
oven, the temperature in the oven must be less than 50 degs C when the
boards are put in so that the chemicals in the solder paste can
evaporate. Once the oven reaches the setpoint 219 degs C, the heater
is turned off, and the door is opened. Note, the fan should be kept
running to assist in the cooling.

As for the controller, I'm using a PIC16C84 (for ease of SW development)
, storing the setpoints in EERAM. The temp sensor is a platinium PT100
sensor, expensive, but very linear in its response. This is in
a bridge, then amplified and fed into a LTC1285 12bit differential A/D.
Note, a 10 bit A/d would do the job though. The controller has a 8
char LCD, and three pushbuttons. Mode, Stop, Start. The S/W is being
written with the CCS C compiler.

The setpoint sare user selectable. When the oven is turned on, the fan
is started, as is the heater element (via relays). Once the setpoint
is reached, the heater is switched off, the oven "Bings" a la microwave
to inform the operator to open the door. Once the temp has dropped to a
temp that the solder has set, another bing is emmited. Once the temp has
dropped to below the 50 degs C point the fan is turned off.

I'm also including a serial port so that the controller will interface
to multimeter logging software. Whenever the controller received the
'D' character it transmits the current temp, ie; "205.1 C". This will
enable me to capture the temperature profile.

Once I get further down the track I let you know how it goes.

I have purchased a vacuum Pen pickup with a vacuum pump and plan to see
if I can convert a fish tank pump to supply the vacuum.

Once I get further down the track I let you know how it goes.

I interested in how you get on.


Peter
--
Peter Homann   email: peterh@adacel.com.au       Work : +61 3 9596-2991
Adacel Pty Ltd                                   Fax  : +61 3 9596-2960
250 Bay St, Brighton 3186, VIC, AUSTRALIA      Mobile :     014 025-925
http://www.adacel.com.au     Australian Software Engineering Excellence