Custom assembly creates ideal flexible heater solution

July 19, 2016 in Case Study

Custom assembly created for flexible heater application

One of our customers in the biotechnology industry contacted us about a set of simple flexible heaters. The designs were very straightforward, with a heater element and a set of wires for power and temperature control. For all intents and purposes, it seemed like a very standard project.

However, as the prototypes were tested in the application, the customer immediately recognized multiple challenges.

The application required the heaters to be sandwiched between two aluminum blocks, which posed a set of issues. The solder joints didn’t allow the blocks to be fully seated on the heaters (see figure 1) because they were higher than the pocket designed to capture them. Also, the adhesive on the bottom of the heaters did not stick well to the aluminum under the solder joints (see figure 2). This created hot spots in the application, recognized by the fused heater element, and wouldn’t allow accurate operation of the apparatus (see figure 3).

fig1

Figure 1

fig2

Figure 2

fig3

Figure 3

Challenge:

 There were two identified challenges: The solder joints were too high and the heater didn’t adhere well under the solder joints. Both of these issues had to be fixed for the project to be successful.

Solution:

 Tramonto designs for application, which means we build the best solution based on how it will be used. Sometimes, that means rethinking the manufacturing process.

The heaters were made with a unique nickel/copper alloy that requires more heat and time than normal soldering procedures to ensure a robust joint. The current joints were soldered according to industry standards and covered with flexible epoxy so that they wouldn’t fracture during normal handling in the assembly process.

Given our customer’s feedback, we analyzed the height of the solder joints first and found that if we spread the strands of wire out like a handheld fan, we could make the solder joint much flatter than the original. This out-of-the-ordinary cable assembly required additional effort, but was necessary to solve the problem.

To ensure full attachment of the cable, we tinned the wire strands in a solder pot, then used only the solder on the strands to attach the wires to the power contact pads. This resulted in a very flat solder joint with full attachment that took less time and heat than the previous operation. We applied the epoxy to the flat joints and constricted the height of the epoxy to the height of the wire’s insulation as a maximum. This created a robust solder joint that allowed both plates to mate solidly with the heaters and remain intact after handling.

Our next and final challenge was to examine the special pressure sensitive adhesive (PSA) that was used under the solder joints. This PSA was on the bottom of the heater to allow adherence to the aluminum plates. Standard processes apply the PSA to the circuit during manufacturing so that when the circuit is removed from the panel, the PSA is aligned perfectly with the circuit edges.

Because of the conductor material used and the amount of heat required to solder the cables, the PSA was being compromised under the contact pads. We had to revisit the industry standard to create a better solution that would stand up to the solder process.

We decided to manufacture the adhesive separately and apply it after the assembly and cleaning processes, requiring a custom fixture to align the adhesive accurately and consistently. This additional step resolved the problem so the heater adhered well under the solder joints.

Result:

 By changing the manufacturing process and providing a non-standard assembly, Tramonto created a very flat heater that adhered well to the aluminum plates. The new design also ensured that the customer didn’t have to change their housings or machined parts, saving them both time and expense.

Normal industry standards do not work for 100% of electronic assemblies being designed by today’s innovative engineers. By creating custom processes when everyday procedures don’t work, Tramonto’s experienced engineers help solve the problems our customers encounter.

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