Automated Printed Circuit Board Assembly (PCBA) Test for Transdermal Electric Injection Device

September 24, 2018

Introduction 
Medical treatment in today’s health-care environment can look less like technology and more like magic or science fiction. Imagine a physician, veterinarian or other health professional with the capability to deliver treatments or medication to a patient through the skin without a needle. What if the treatment could then take effect within seconds? It can. And it’s not magic. Let’s take a closer look at a new technology based on existing principles.
 
Product
The product includes a battery-powered wand containing a cartridge of liquid inserted by a nurse. With a silent push, fluids are forced through the skin using a small electric current. While the electrical signal is almost unrecognizable to the patient, who may experience a mild tingling sensation, it causes the muscle cells below the skin to expand and accept liquid faster. 

The device is comprised of a circuit board with a small motor for activating the syringe cartridge, electrodes for detecting contact with the skin, and circuitry for applying the voltage and current in a carefully controlled process. To make the device handheld, the circuit board is divided into several boards connected together to fit into the wand. 
 
Challenge  
Cyth was challenged to prepare the circuit boards immediately after the components are soldered into place. This process entails:

 

•    Uploading firmware to the microprocessor and dedicated safety processor
•    Powering on the device and charging the internal capacitors while monitoring the circuit performance
•    Testing the operation of high-speed voltage and current control circuits
•    Instructing the board to perform operations like moving the plunger motor
•    Testing the safety circuit with a variety of modes to emulate skin types and product issues
•    Emulating the plunger motor so the board recognizes that the motor is real

 

Some of the necessary tests were simple, such as a resistance test to open and close a relay. Cyth also built mechanical fingers to test the function of a few buttons and to cover a light sensor. Voltage was tested for a certain tolerance, and we ensured that the boards controlling two LCD screens worked properly and were sensitive to touch as appropriate. 

Finally, Cyth performed testing to confirm that the board successfully connected to the PC through the firmware interface. Three of the boards use high voltage, so we conducted high-voltage switching tests on two of the boards at high speed. This required two different DMMs in the PXI, which can become expensive for running multiple tests. Cyth reduced costs by utilizing a relay bank with Switch Executive that allowed for reuse of the DMMs and various power supplies. 
 
Solution 
In collaboration with the client, Cyth developed a bed-of-nails fixture mounted on top of a custom-made rolling cart. The cart housed the electronics and also acted as a workstation. Inside the cart’s cabinet was the hub of operations – a PXI System that provided the instruments to program and control the boards, including sending signals and taking measurements at various points on the boards. 

The bed-of-nails fixture was designed to house all seven circuit boards in a way that they would be electrically connected to one another, but so that any one of the boards could be tested without the others present – a significant challenge. 

For some of the more extreme signals, such as very high voltage or current, specialized bench top power supplies were used along with a battery simulator. Together, the system was able to perform all of the tasks and tests to certify each device according to the test plan and to FDA standards. For more details on every test step and measurement, see the “Test Details” section at the end of this document. 

Obstacles
The most significant challenge was understanding the entire test plan. During the initial design phase, and at certain points throughout the development process, there were discoveries and scenarios such as missing test points on the prototype boards and the fact that some of the firmware was not yet developed. Cyth collaborated with the customer to suggest workarounds with hardware, test method, or development schedule in an effort to keep the project moving forward in a timely manner without significantly affecting the budget. Challenges like these are very common with a new product introduction for manufacturing.

At the same time, much was learned about the proper function of the device and how it interacts with human skin in clinical trials. If an expected waveform was described by the scientists, and generated by the device, Cyth’s test system could quantify and confirm the signal to within a microvolt or a microsecond of correct performance. Likewise, if the system detected any issues with the signal, the design team would request data or waveforms to help them understand how the circuitry was behaving – or misbehaving.

As various clinical scenarios were tested with skin types characterized by their moisture content, impedance, or temperatures, changes could be implemented or evaluated on the test system and new limits or requirements could be set.  
 

Results
Despite a long road of modifications and learning, the system met all functional requirements and passed its Site Acceptance Test and FDA validations. The system is currently in use producing devices and has been modified a few times as the product evolves and is updated for its second generation. As production volumes increased, the customer managed to run the system into a second shift, but discussions are underway regarding a second system to allow for volume growth in the future. 

 

Impact
Cyth provided an automated testing process for a device that has the potential to revolutionize how vaccines and treatments are delivered for both safety and effectiveness. New medical devices are being developed everyday around the world. The client has a unique technology with the capability to change or save lives, but it must be thoroughly tested for safety in both the design and manufacturing phase. Cyth’s ability to build custom systems like these is what makes Automated Test Equipment so valuable and rewarding to work on.
 

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