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Close collaboration between engineers and manufacturers leads to the successful design of custom components, according to Joe Moxley, senior engineer at Custom Electronics.

In today’s market, fewer and fewer design engineers can purchase standard components from a distributor’s warehouse.

Facing increased demands for minimal size and maximum reliability, these engineers instead need custom components that meet individual specifications.

While custom work eliminates the problem of wasting resources on standard components that exceed size, weight and voltage requirements, custom jobs can introduce other complications.

In order to create successful outcomes, design engineers and component manufacturers must collaborate closely.

When an unexpected issue arises, solving it depends upon the strength of the relationship between the engineer and the manufacturer.

For instance, if a customer is dissatisfied with its capacitor supplier because of failures in the application, the manufacturer might also get frustrated.

The capacitor, designed according to standard specifications, might appear fine under testing analysis, even though the customer reports it fails in application.

The problem might be that the capacitor is mounted too closely to the printed circuit board, creating stray capacitance between the capacitor body and the board.

Because the capacitor thus formed in parallel with the mica paper capacitor is much lower in capacitance to the mica paper capacitor, the voltage stress is much higher and causes the circuit to short between internal connections in the mica paper capacitor and the printed circuit board.

Had the design engineer known that guideline from the beginning of the design process, an extra wrap of mylar tape around the mica paper capacitor would have provided the additional dielectric strength to prevent the arcing and solve the problem.

This kind of issue is difficult to correct, can cost both companies time and money and can be easily resolved through open communication and collaboration.

Design engineers should share all potentially applicable information with component manufacturers at the start of a project.

These details include: temperature, shock, vibration, atmospheric pressure and electrical stresses.

In many applications, all of these elements come into play and must be considered during the design stage.

A close working relationship between engineers can lead to many benefits.

If, for example, during discussions about how certain mica paper capacitors should be moulded it is found that resistor, diodes and other components are needed in the assembly and are part of the calculations of what space is available for the capacitor, the components can be assembled with the mica paper capacitor and moulded assemblies as single units, saving space and offering convenience for the customer.

Custom shapes to moulded units can also provide mounting options for other devices.

In addition to custom shapes, custom electrical terminations and mounting hardware can usually be integrated into the moulded unit to offer more space and weight savings.

These are benefits that can only be realised through the sharing of detailed information.

When design engineers and component manufacturers collaborate on accelerated life testing, they can also reap rewards that maximise design efficiency.

By testing samples of the desired capacitor at multiple elevated stress levels that are similar to the actual operating stresses, the capacitor will experience an accurate prediction of when and how it might fail.

These predictions can be made in a relatively short time.

An aircraft ignition system’s capacitor provides a clear example of how collaborative testing can affect the overall success of an application.

The process should begin by making samples of the desired capacitor with less mica paper dielectric than usual, for example, 10 units with 2.6 mils paper thickness, 10 units with 2.8 mils paper thickness and 10 units with 3.0 mils paper thickness, where the normal design criteria would call for 3.6 mils of dielectric.

Using a spark gap of the same breakdown voltage and using circuitry as close as possible to the finished unit provides three levels of voltage stress.

By using different oven temperatures of 85C and 125C, there are two levels for temperature stress.

Engineers can increase the pulse rate of the spark gap to speed up the process even more.

At 20Hz, companies can achieve 1.0 x 10 to the power of 8 pulses in less than two months.

With data from test procedures, the probability density function of each of the various stress factors can be graphically represented and used to calculate the acceleration factors for volts per mil stress and temperature.

Using that information, manufacturers can predict life at any given voltage or temperature with a certain degree of confidence and reliability.

Customised components offer several benefits to design engineers.

Rather than grappling with standardised products that exceed application needs and waste resources, companies can bring individual needs to the table before components are even formed.

To ensure successful outcomes, manufacturers and customers must work closely together with open, detailed communication.

Custom Electronics

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