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    # Non-solder bootloader
    
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    This doohickey can be used to flash a bootloader or a binary onto a SAMD21E without soldering it. This is useful when the final board for the SAMD21E is too small to afford having a swd connector.
    
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    ![](img/use.jpg)
    
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    This is still experimental and not 100% reliable, but the board simply consists of copper traces onto which the QFP32 chip is pressed with a 3D printed jig. The 3D printed part is compliant and presses on each leg adequately.
    
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    This board features a SAMD11 as a permanent USB-to-swd programmer so that flashing is as simple as plugging the board in and launching edbg or the [Arduino core](https://gitlab.cba.mit.edu/quentinbolsee/Arduino-SAM-tutorial/).
    
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    ## Design
    
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    ### Schematic
    
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    The schematic is the bare minimum, with a SAMD11 as a USB-to-swd programmer connected to the target SAMD21. The fact that the SAMD21 will not be soldered is not visible in the schematic, or the board design for that matter.
    
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    ![](img/schematic.png)
    
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    An LED is connected to pin PA00 of the target SAMD21, in case you want to flash an LED blinking code onto it to make sure it's functional.
    
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    ### Board layout
    
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    The board design is split in two: the USB and D11 programmer on top, and the non-solder area on the bottom. Note that only a few pins are connected on the target, the bare minimum plus an LED for testing.
    
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    ![](img/board.png)
    
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    M3 holes allow for future improvement on the pressing method, the spacing is:
    
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    - horizontal: 1.2in
    - vertical: 0.8in
    
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    The png images for fabrication can be found [here](design/png) and the kicad files [here](design/kicad).
    
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    ### CAD
    
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    The press has a lip on its bottom side to apply load directly on the legs of the QFP32 target. There is still some improvement needed there but it works for now.
    
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    ![](img/press.png)
    
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    The 3D files can be found [here](design/cad).
    
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    ## Making
    
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    The board can be milled with a 1/64" flat end mill:
    
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    ![](img/milling.jpg)
    
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    After removing all of the extra copper with a 1/32" end mill (for speed), the board looks very simple:
    
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    ![](img/milling_done.jpg)
    
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    After flashing the [free-dap](https://github.com/ataradov/free-dap) on the SAMD11, you can attach a SAMD21 target with M3 screws and launch a flashing like you normally would when using a programmer.
    
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    ![](img/use.jpg)