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Workbench Wednesdays

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A long time ago, I made a video suggesting math was unnecessary to determine proper pull-up resistor values. Like most generalized statements, that suggestion is not always true. For example, in data buses like I2C, speeds like 400 kHz and 1 MHz are common. At those speeds, the pull-up resistor and the bus capacitance form an RC filter that fundamentally limits the data transmission speed. Or. It limits the range of pull-up resistor values. In this Workbench Wednesdays video, I show how to estimate I2C bus capacitance, measure that capacitance, and pick pull-up resistor values.

In August 2022, Nordic Semiconductor announced its first Wi-Fi product. The nRF7002 is a dual-band (2.4 and 5 GHz) Wi-Fi 6 compatible companion IC. It does not have a general-purpose microcontroller built-in. Instead, Nordic intends for you to combine it with another microcontroller, like one of their nRF52 or nRF53-series system on chip (SoC).

During the component shortage, I got to know Raspberry Pi’s RP2040 microcontroller. It is a dual-core Arm Cortex-M0+ with about 262 kilobytes of RAM. The feature I like most is the programmable IO pins. These are small state machines that run independently of the Arm cores. They allow for some clever tricks. For example, I used them extensively on the Mega IIe project.

Often I hear this question: “how can I get better solder joints?” Without looking at anything they are doing, I already know that they could be using more flux. Or, as I point out in this video, perhaps the correct type of flux!

Flux removes oxide layers, gets contaminants out of the way, and makes for better solder joints. But there are so many different types of flux and even more ways to apply it.

This video goes over the different types of Rosin (R, RA, RMA), Resin, Organic, and Inorganic flux. Then it shows what kind of residue gets left over. And explains why “NO Clean Flux” actually needs to be cleaned (in most cases).

What is No Clean Flux?

In the video, I make the bold statement that “no clean” is not a type of flux. I know some people will take issue with that. However, based on the IPC chart for flux bases, “no clean” is not one of them. And if you look through datasheets, you’ll find lots of variations of what manufacturers call “no clean.”

From what I can tell, “No Clean” flux is generally a Non-activated or mildly activated Rosin or Resin type. The remaining residue is non-conductive and non-corrosive. So by that general definition, many fluxes can be marketed as “No Clean.”