Sap Flow Gauge Build Steps

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Kevin Xu March 2020


After you have your PCBs and parts, you'll need to assemble your gauges using the following steps:

  1. Apply solder paste on each of the exposed PCB pads.
  2. Place each component on the PCB in their corresponding spots (i.e., on top of the solder-paste-topped pads).
  3. Bake the PCB with components in a toaster oven (which you'll never use for food, as the fumes are hazardous).
  4. Manually re-solder defects.

Apply Solder Paste

Using either a syringe or stencil, apply solder paste to the exposed pads of your gauges:

Sapflow Solder Paste

Place Components

Using tweezers, place each component onto its pads:

Sapflow Oven Rack

Bake the PCB with Components

Insert the PCBs with components into a toaster oven (which you'll never use for food because again, these fumes are toxic) set to 450 degrees F (or 230 degrees C):

Sapflow Oven

Keep the PCBs in the oven for ~10 minutes:

Sapflow Oven2

Manually Re-solder Defects

In all likelihood, there will be some defects in the solder reflow process:

Sapflow Reflow Errors

Often, you'll see solder bridges (e.g., multiple pins of the HDC2080 incorrectly soldered together) and tombstoning (e.g., resistors and capacitors rotating due to solder only reflowing onto one side of the component):

Sapflow Reflow Errors Circled

In these cases, you'll need to apply flux and manually re-solder the defects.

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