I’ve been playing with cheap OLED display breakouts for years, incorporating complete boards into my projects – an easy, but bulky solution. Now that I’ve had some practice designing circuits and PCBs, it’s time for my next challenge: soldering the display FPCs directly to my own boards.
I designed this board to try out a minimal circuit before integrating it into any larger projects, and to figure out the best way to solder flexible circuits to my boards. Since all of my new microcontroller-powered board designs only require 3.3 V, I haven’t added any 5 V tolerant level shifting. What’s left is a bare minimum circuit to drive a Solomon Systech SSD1306 using SPI at 3.3 V.
The capacitor values stated in the schematic are based on the sample circuit design from the datasheet, derated for DC bias while keeping their size at 0805. If you decide to use a different brand or series of caps than the ones listed in the BOM, remember to check the DC bias graph in your datasheet to select the appropriate values.
As you can see, when I say minimal I do mean minimal. There’s not much to the design, other than a few capacitors and resistors (including a pull-up resistor for the SPI chip select). The top corners of the PCB are rounded, while the bottom corners have right angles to match the OLED display. Unfortunately this design still uses my old hand soldering-sized footprints, but they’ll work just fine for hot air as well.
If you’d like to make your own breakout, you can use this shared OSH Park project to either download the KiCad board layout, or order some bare PCBs.
Soldering FPCs to PCBs
The OLED display won’t survive hot air soldering, so I’ve had to fall back on my Hakko FX-888D. Ideally you would use hot-bar soldering to connect the FPC, but most of us won’t have the needed equipment sitting around. The next best thing, in my opinion, is a knife tip (Hakko’s K shape), which is what I used on the board shown below. An alternative option might be Hakko’s Spatula shape, provided it doesn’t wick away all of the solder. I haven’t had a chance to try a spatula tip yet, because the Hakko one isn’t compatible with my soldering iron series.
1) Add solder paste to the pads (including the FPC footprint) manually or using a stencil.
2) Place the capacitors and resistors on the board, but leave the FPC footprint unpopulated.
3) Reflow all of the pads.
4) Line up the exposed pads on the FPC with the top edge of the footprint on the PCB. When lined up properly, the FPC’s pads should overlap roughly 2/3rds of the length of the PCB’s pads. You can optionally tape the FPC to the board with kapton tape, to prevent it from moving around while soldering.
5) Hold the knife tip perpendicular to the pads, and place it on top of the FPC where the PCB pads start. Now drag it down the entire length of the pads, a few at a time (similar to this). Don’t add any additional solder to the pads. Some flux can’t hurt though.
Bill of Materials
|C1,C3,C4,C5||4||MLCC 1 µF X7R 10%||0805||Murata||GRM21BR71H105KA12|
|C2||1||MLCC 2.2 µF X7R 10%||0805||Murata||GRM21BR71E225KA73|
|C6||1||MLCC 4.7 µF X7R 10%||0805||Murata||GRM21BR71E475KA73|
|R1||1||Thick film 390 kΩ||0805||Panasonic||ERJ6ENF3903|
|R2||1||Thick film 10 kΩ||0805||Panasonic||ERJ6ENF1002|
|U1||1||SSD1306 1.3″ OLED display||–||EastRising||ER-OLED013-1W|
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