Calibration slides: a boon for measuring small things like the dimensions of solder pads on surface mount components

One of the calibration slides, with the 1-mm-per-division scale above a surface-mount CO2 sensor. — One of the calibration slides, with the 1-mm-per-division scale above a new surface-mount CO2 sensor from Sensirion. I hadn’t aligned the start of the scale with the left side of the sensor yet, but it’s 1 centimeter (10mm) square.

The trend seems to be that the share of interesting new thingamajigs and doodads available only in tiny packages will inexorably increase and the availability of the same stuff in through-hole and DIP package form will inexorably decrease. As a dabbler, I don’t need to weigh in and deliver some comprehensive, well-reasoned, and defensible point of view on the shift, which has been going on for a long time. Obviously, it will continue to make breadboarding (solderless breadboards) less useful and relevant beyond really introductory-level tinkering. It would also seem to tend towards making gear like microscopes and at least pro-am/home-gamer versions of reflow ovens, hot air pencils, etc. more needful.

For some components, adapter PCBs may be available. Each such beast features the footprint for a certain package type and size (often expressed in terms of the number of pins or terminals it has), with the solder pads to match, linked via traces to rows of plated holes for pin headers along two sides. Once you’ve soldered the non-DIP component and lengths of pin header onto the PCB, you can press it into a breadboard and get to prototyping your circuit. Less permanent and usually at a significantly greater cost are test sockets.

The data sheet for a given component will usually include a section specifying the physical dimensions of the overall component, the sizes of the pads or pins, their spacing, etc. But you may sometimes want or need to use parts for which the data sheet is light on such details or for which you don’t have a data sheet or you may want to verify the information or get a feel for the relative size of, say, the stripped end of a length of wire versus the size of a solder pad on the part or make other precise millimeter-and-below measurements.

I used the one-centimeter-total, tenth-of-a-millimeter-division scale (leftmost of the four scales printed on that slide).

One tool that’s available are calibration slides, microscope slides on which one or more scales have been printed. I recently picked up several, of a couple of types, and played around with using one to gauge the dimensions of the solder pads on the bottom of a new-ish surface-mount CO2 sensor, the Sensirion SCD41.

My setup for these photos utilized a mini PCB vise and some heavy notecard paper, cut to shape. The tweezers were used to gingerly nudge the slide and the component (mostly the component).

I used a small PCB vise with plastic covered posts that could be moved from one hole to another on the top faces of the vise’s jaws. After narrowing the spacing in the pairs of posts enough that all four would be supporting the calibration slide, I cut some heavy notcard paper to size and shape and placed it over the vise’s screw and guide bars. The SCD41 rested atop the paper and beneath the slide.