Programming the CRICKIT for Selective Soldering: a Deep Dive PART 3 @Adafruit #CRICKIT #manufacturing #selectivesoldering
You’ve made it to part 3 of the CRICKIT programming deep dive. Woo-hoo!
So far we’ve discussed our thinking behind the CRICKIT’s panelization as well as some guiding principles that underpin our programming philosophy. Now let’s get to the actual CRICKIT program itself!
Order of Operations
Although you may go about it in a number of different ways we tend to lay down our flux paths FIRST. We like to sketch the flux paths first because the board will always be fluxed prior to soldering.
We begin by merely sketching over the necessary leads we know we will be soldering. Remember, it’s too early to begin optimizing. We can start tweaking once we’ve seen how the program runs.
We then begin sketching the solder paths ATOP the flux paths…
Once we have The flux and solder paths roughly sketched we take a look at the actual components we’re going to be soldering.
Solder Height & Component Lead Length
The “solder height” is the distance below the datum measured from the nozzle face…
The datum, or reference plane in this case is the underside of the pcb. This reference height is 0.000 in coordinate space. Therefore the overwhelming majority of solder height values are will be preceded by a negative sign because the nozzle will be soldering BELOW that datum. We would only be soldering in the positive direction if the board was resting inside of a fixture which raised the board above that datum.
The “nozzle face” is the top of the nozzle once it’s seated on the solder pump.
The CRICKIT board has a total of seven components that required selective soldering and six of those seven were effectively different from each other.
Due to these differences in lead length as well as pitch we knew from the outset that we would have to create individualized solder heights for some of our components. We grouped these components accordingly:
headers: (1) 3 x 4 male header, (1) 3 x 8 female header
We grouped these as such because each group contained identical lead length, pitch and mass.
Our inital plan was to use a 6mm nozzle for the entire board. We drew multiple solder paths to cover the headers and barrel jack. We soon discovered however that we weren’t getting sufficient coverage and the cycle time was rather long. We then decided to to try using a 9mm nozzle for the headers and barrel jack instead of the 6mm nozzle.
We were hoping that with sufficient flux deposition the 9mm nozzle would successfully solder the headers without too much bridging. Now that we were using a larger nozzle we also knew we could cut down on the number of paths needed to cover the headers as well as the barrel jack’s leads which would theoretically result in a savings of time. Below is a picture of the very first CRICKIT test run:
Not too bad for a first run!
Join us in part 4 of this deep dive as we discuss further refinements we made to our CRICKIT program. I promise you won’t wanna miss it!
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