Reflow soldering - Part (4) First soldering test

Plot of actual temperature change

The board I used for the test, SMD 1206 resistor centre

I have been experimenting with the oven under the control of my programmable temperature controller, ( see 12 December ), and making minor changes to the software until I obtained the heating and cooling characteristic above. It closely resembles the ideal profile, ( see 8 October ).
Eager to try some soldering, I put several blobs of solder-paste and a surface-mount resistor on a scrap piece of copper clad circuit board material, placed it in the oven and started the process. After completion I inspected the board. The solder-paste had become metallic, the resistor was nicely soldered and the copper hadn't 'lifted'.
Without any stencil, I had applied far too much solder-paste.

Reflow soldering - Part (3) Temperature controller

Controller unit with SSR and thermocouple wire connected

Internal view - MAX6675 on mini board alongside PIC

I have made another oven temperature controller in a convenient to use enclosure, which has a sloping surface for the back-lit liquid crystal display module. It looks quite professional. The circuit is the same as the earlier experimental version, ( posted on 11 November ), using a PIC microcontroller and MAX6675 temperature sensor chip. It is ready for integrating with the oven. The output of the 15 amp solid state relay ( SSR ) has to be connected in series with the mains lead to control the power. The thermocouple will be situated inside the oven eventually very close to, or actually touching, the circuit board which is being soldered.
I am thinking that it would be beneficial to add a programming interface to the controller so that I can re-program the embedded PIC in-situ.

Digital thermometer

Arduino 'Uno' board and temperature sensor board

L: MCP2210 USB to SPI; upper R: LM35D; lower R: MAX6675

My fun with measuring temperature continues while waiting for the solder-mask stencils for reflow-soldering to be prepared. I have been using the LM35D temperature sensor chip. It doesn't require a thermocouple as the chip itself produces a voltage related to its own temperature, ( 10mV per degC ), and because the chip generates almost no heat, its temperature is nearly identical to that of its immediate surroundings. It's accurate to within about 0.5C. This time, because my DIY development board, ( MYDEV2 ), is otherwise engaged, I have been using my Arduino 'Uno' board with Atmel Atmega328P-PU microcontroller. I use the Arduino's analogue to digital converter to sample the voltage produced by the LM35D and then I process the 10 bit digital value to get the temperature for displaying. For no reason other than to use the second row on the display, I've also added a timer to count the seconds which have elapsed since the last program upload or reset.

I might make another for use as the workshop's digital thermometer.