Parts

103 ASSEMBLY, ALIGNMENT FIXTURE

This is the primary alignment fixture assembly used to align the thermoelectric pillars & hold them in place during the soldering process. Careful material and design tolerance analysis ensures the pillars will be accurately placed within 0.25mm of their target nominal locations.

101 ALIGNMENT COMB

These combs, cut from Kovar Nickel using extremely high precision wire EDM, provide an accurate, stiff and strong support for pillar placement. Kovar's low coefficient of thermal expansion matches the ceramic plates used in the assembly and prevents unwanted shear or seizing.

102 FIXTURE BASE

The alignment fixture's base, precision-machined from 6061-T6 aluminum, is capable of resisting temperatures of over 500°C as well as day-to-day rough usage. When heated, it out-expands the other components used in the fixture to prevent any sort of galling, seizing, or other unwanted interference.

104 FIXTURE TOP ALIGNER

The "cap" of the assembly fixture, this removable plate locks the upper ceramic plate & electrode carrier in place. Precision-machined from 6061-T6 aluminum, this component has been carefully toleranced to ensure a clean fit in any situation.

106 FIXTURE, SOLDER APPLICATION

This fixture, designed for 3D printing with a resin printer, locks the solder stencil in place above a ceramic plate with an electrode layout for ease of solder paste application. Careful height dimensioning allows a solder squeegee to cleanly spread solder across the stencil. In the event of thicker or thinner ceramic plates, shim stocks can be used to change fixture height to ensure a flush solder spread.

Solder Stencil

The stencil was custom made in order to accurately place the solder paste onto our alignment of thermoelectric pillars. Sourced from Stencils Unlimited, this stencil was created using a high-precision UV laser, and is made from flexible yet durable aluminum. At 0.1mm (.004") thick, the stencil places just enough solder at each pillar-electrode junction to ensure a solid bond without any risk of solder drip or run.

Solder Reflow Oven

The purpose of the oven is to heat the fixture up to the solder reflow temperature.

This particular oven (Toshiba Convection Toaster Oven) was chosen for testing because it can reach a max temperature of 230°C in about 5 minutes and has a built in convection mode which makes it easier for the hot air to reach inside the fixture and melt the solder paste.

Additional testing using a K-type thermocouple determined that this particular oven is capable of holding a given target temperature with an error of +/- 2°C, rendering it more than effective for accurate process testing purposes.

For further development and production usage, an industrial solder reflow oven is suggested for optimal outcomes.

ChipQuik SMDLTLFP50T3 Solder Paste

Solder paste is needed to solder the thermoelectric pillars onto the copper electrodes.

The solder paste is applied onto the copper electrodes using a stencil. This solder paste was chosen as it is lead-free (RoHS compliant) and has a low reflow temperature (165°C).

WD-40 PTFE Dry Lubricant

Teflon (PTFE) Dry lubricant serves two purposes:

1) Provides solder masking to prevent solder from dripping onto undesired locations in the fixture.

2) Lubricates combs to reduce friction when removing them from fixture