Manufacturing Tests on Embedded Devices

Modern day embedded devices have a lot of components. For example, a digital control panel we recently developed had 4 processors, voltage regulators, a seven segment display, several LEDs, a real time clock IC, thermocouple circuitry, several passives, FETs and relays placed on an FR4 PCB. This magnitude of components means the device manufacturer needs quick and strong testing routines to test the boards as they are being made.

The way we tested this digital control panel is very interesting.

The first step was to specify and confirm with our CM (Component Manufacturer) that the PCB house that is making the PCBs is running electrical tests on the bare boards being sent to us.

The next step was to ensure that all components were working on those boards after pick and place assembly. During this step it is very important for us to mandate the CM do visual inspection on these parts. This usually is a good way to eliminate solder blobs etc, which could short and damage processors. Once this is complete, the manufacturer may power the boards and continue testing the operation of the components. For this, a simple test hardware, firmware and/or a GUI application that collects feedback from all the components placed on the board needs to be run. In the case of the digital control panel specified above, we developed a Windows forms application software that communicated with the control panel via USB to test proper functionality of the production units by the component manufacturer. Since there were external inputs and FETs that needed to be tested, we also created some custom hardware to verify the components.

OEMs run into situations where the sourcing is delayed due to factors beyond their control such as weather etc. Under such circumstances, when the customer wants parts yesterday and manufacturers are still trying to source and assemble the unit it may be beneficial to automate some or part of the tests. In the case of the digital control panel communication tests between processors and testing each segment of the seven segment display was automated.

The final step involved checking functionality at the manufacturer’s site. In the case of the digital control panel, we programmed all the processors with the final product code and tested the devices after assembly for operation. This procedure can also be provided to the end client for acceptance testing.

If the number of units manufactured in one production run is a few hundred pieces, it may be okay to test all the units. However, as quantities increase to a few thousands, automating step 2 becomes more important. This would give the device manufacturer the freedom to not perform step 3 or to perform step 3 only on boards that exhibited issues during step 2.

Sometimes, a lot of engineering cycles are spent in developing a product with very little thought on how you may actually test it during manufacturing. In such cases outside testing experts such as ourselves, Blue Sparq, Inc. can be used to develop test equipment and/or test cases for your production runs.

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