Thermal components for military, aerospace, and medical applications are continually getting smaller, more accurate, and more robust. To match these technological advancements, heating systems are being custom-designed to provide critical edge-to-edge uniformity, tight dimensional tolerances, and integrated sensors and flex leads to create complete thermal solutions.

Figure 1. The 384-Well Microplate, filled with reagents, slides into the PCR sample block and heater. Each heater hole fits around the wells to provide optimum heater transfer.

Proof of this technology trend is a 384- hole heater designed for integration into high-throughput polymerase chain reaction (PCR) thermal cycling applications in the medical diagnostics industry. The flexible, etched heater maintains temperature uniformity across a 384-well PCR sample block, while reagents are cycled in wells from 37 to 105°C through the three cycle steps of denaturing, annealing, and extension.

Custom-profiling the heater element provides efficient and accurate thermal management of the PCR application. The profiling process includes chemically etching the foil element to provide more heat around the edges, where heat loss typically occurs, compared to the middle, where heat loss is less of a problem. Profiling the heater element allows it to maintain ±2°C uniformity across the PCR sample block.

The well holes are trimmed using laser technology that enables extremely tight hole-to-hole tolerance. This allows for accurate registration of the heater to the PCR sample block. The laser trimming process can provide a tight positional tolerance of ±0.002" (0.05mm), which is more accurate than steel rule dies and other trimming techniques. The net effect for the PCR application is that the heater aligns with the sample block and cuvette tray/microplate. Equally important, the reaction process can be viewed without infringement by the heater. Thin and flexible, the construction of the 384-hole heater can save valuable space. Typical heater thickness ranges from 0.005" (0.13mm) to 0.012" (0.3mm). The minimum bend radius is 0.030"(0.8mm). The heater is constructed with a polyimide substrate. Pressure-sensitive adhesive (PSA), epoxy, factory lamination, or a mechanical clamp can be used to affix the polyimide heater to a heatsink.

Figure 2. The Heater is trimmed using a laser that enables tight dimensional tolerance.

Sensors and flex leads can increase performance and control of the thermal transfer. Precisely integrating a resistance temperature detector (RTD), thermistor, or thermocouple into the heater eliminates the need for extra drilling and supporting sensing systems. A flex lead maintains the spatial arrangement of the heater and creates a connection point that’s free of solder connections.

The technology used to create the heater can be leveraged to fit any application where uniformity, accuracy, and ruggedness are critical features.

This article was written by Brian Williams, marketing manager of the Heaters Division at Minco, Minneapolis, MN. For more information contact This email address is being protected from spambots. You need JavaScript enabled to view it.

NASA Tech Briefs Magazine

This article first appeared in the November, 2005 issue of NASA Tech Briefs Magazine.

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