24 Aug Upgrading a cheap Chinese surface mount oven
I sometimes have the need to make many surface mount printed circuit boards. Typically these take me about 30 minutes per board to make manually with a soldering iron. I have been looking for a way to improve this time.
Surface mount PCBs are made professionally by applying a solder paste to the printed circuit board where the pins of a component are needed to contact the PCB. The component is then placed onto the paste, and is held there by it.
The entire board is then run through the reflow oven. This surrounds the PCB with hot air greater than then melting point of the solder paste. After a pre-determined time, the paste melts and the system is cooled under control to prevent thermal stresses building up.
Professional reflow ovens can cost £10000+.
However, the T962 oven is a generic Chinese built reflow oven that is available for less than £160. It gets mediocre reviews as delivered. But it can be upgraded…..
As delivered the unit has several faults:
- It smells when operating. This is because a cheap masking tape like material has been used in it’s construction. Fix: Replace tape.
- There is an internal fan to control the temperature, but the software controlling it is sub optimal. Fix: New software.
- The temperature sensors are not installed correctly. Fix: Add new temperature sensor.
- The electrical case earthing is unsafe. Fix: Renew earthing.
There are several videos describing how to overcome these faults, I found the best one to be the one posted by Nick Williams.
I started by replacing the masking tape that causes the smell with high temperature Kapton tape that I use on my 3D printer bed.
The rest of the issues I followed from the video. And after re-flashing the controller firmware and installing a new temperature sensor I was presented with a new display of:
And so to try the first PCB.
I had designed a surface mount PCB using the free package Design Spark.
To ensure that the solder paste was placed correctly, I use the laser cutter to cut holes in a sheet of mylar film where the solder paste needed to be placed.
To ensure the PCB was aligned with the mylar film, I created an alignment tool which holds the PCB in place, and has two posts which align the mylar sheet:
A layer of balsa wood that is the same thickness as the PCB ensures that the mylar sheet and the PCB are at the same level.
With the mylar sheet in place, it is a simple taste using a squeegee to apply the solder paste:
With the mylar sheet removed, each component pad now has an area of solder paste applied. The paste can be seen on each pad:
Now the components are placed:
Now the board is placed into the oven. The oven has an inbuilt thermal profile that ensures the board is not heated too quickly, the components are not held at a high temperature for too long, and that the cooling process does not damage the components or their connections:
The modified reflow oven follows the profile very well:
At the end of the cycle the PCB appears thus:
A little rework is required, but the manufacturing time has been cut from 30 mins to 10 mins. Well worth the effort when 20 boards are to be made.