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The reflow oven is used to bake our boards and solder them. In the past, we have had issues with the solder paste not melting fully and thus not creating a good joint. We have also had issues with uneven heating, and soldering multiple boards at once. We would love to be able to fix these issues with the oven instead of doing all the manual rework that we have had to do in the past.


Here are a few guides/reviews of the Qinsi QS-5100 reflow oven that we have:

Purchase Link (probable not where we got it from): https://www.amazon.ca/QS-5100-Drawer-Reflow-Soldering-Machine/dp/B00KDGN9S6

Great forum thread on EEVBlog: https://www.eevblog.com/forum/reviews/qs-5100-reflow-oven-any-tips-warings-etc/


QS-5100 Details

  • Features
    • One sided infrared heating
  • Issues
    • Uneven temperature distribution causing uneven heating and inconsistent solder joint across a board
    • Not CSA certified

Where is the sensor that the oven uses to measure the temp? - it would be great to know to compare accuracy of the results.
It is worth noting that the temperature displayed on the oven is different from the temperature measured on the PCB by a lot - up to 30 C, even in lower temperatures.

General Reflow Tips

  • Preheat the board to bring the board up to temp to reduce the chance of cold solder joints if the whole joint is not up to temp. This is done in the preheat section of the reflow profile
  • Don't make the preheat period too long or else all of the flux will dry out
  • Every component usually has a recommended reflow profile in the datasheet (or at least max temps), as well as the solder paste
    • We will follow the recommendation for the solder paste, as this
  • Three power levels can be set (preheat, heat, and solder) the user can change the temperature of each level and set how long the temperature will be held for 
    • Note that this time does not include the time to get up to said temperature

Setting

Fill this out with the definitions for the various heating times for the Qinsi QS-5100
I do not believe that the rate of heat rise of cooling is controllable from the settings, just the time that it stays at the set temperature.

  • Heat
  • Solder
  • etc.

Recommended Heating Profile

The following figure is from the CHIPQUIK TS391AX50 data sheet. It outlines the recommended profile for the solder paste.

Tips

  • Don't place items directly on the metal rack, raise them with pieces of unused PCBs (from the EEVBlog post)
  • etc.

Testing

We want to make sure that our reflow oven is actually reaching the desired temperatures during the profile. We have purchased a high temperature type K thermocouple that we can place inside the oven to measure the temperature of the boards in real time. We will make sure that this profile lines up with the settings that we selected.

Digikey link for the thermocouple: https://www.digikey.ca/product-detail/en/tpi-test-products-int/GK11M/290-1911-ND/415777
The thermocouple should be attached to the PCB, probably on the top side in the middle of the board, to achieve the most accurate measurement. Use Kapton tape for this.
When testing, take pictures of the test setup so that we can document it.

Can be used with the orange Keysight multimeter (I forget the model number right now) and the Keysight app to export the data. We want to export a CSV if we can in order to easily graph it with excel of python.

It would be great if we could also map a temperature distribution of the PCBs and the oven as well.

Test Results

The following figure shows the temperature of the center of an old PCB over time.

The desired temperature is reached and slightly surpassed, but temperature drops between peaks which could affect the quality of the solder.

 

The following figure shows the temperature of the corner of another copy of the same PCB. The same pattern as above can be observed, but the temperature is notably higher than what was measured in the center of the board.

The following image shows the heat distribution of a PCB after reaching peak temperature. It is difficult to see the temperature across the board, possibly because of the high difference between the temperature of the board and the temperature of the surroundings. The angle of the camera also greatly affects the temperature readings so the hot spots on the left are likely not actually there, and the actual temperature of the board is much more accurately determined from the thermocouple plots above.

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