Test and inspection include multiple aspects of board qualification. Electrical testing and EMC tests are important for evaluating functionality, as well as compliance with industry standards and FCC rules. A manufactured board will also need to pass environmental tests to ensure the product is safe, durable, and compliant. No one wants to produce a batch of boards only to find that they corrode or are not RoHS compliant.
Before your next shipment of finished PCBs arrives at your office or warehouse, you’ll need assurance that it will comply with important industry safety standards and is fully functional. An experienced CM with the right facilities can perform these tests and much more during fabrication.
What Goes into Environmental Testing of Electronics?
Environmental testing is about more than just elevated temperature and humidity tests. A series of environmental tests can include shock, vibration, and mechanical tests. These tests should be performed in accordance with the IEC 60068 environmental testing standards. These tests are intended to ensure a new product can survive under when stored or transported at extreme temperatures and humidity, as well as in the operational environment.
Highly Accelerated Tests
Accelerated tests include highly accelerated life test (HALT) and highly accelerated stress screen (HASS). These tests assess product reliability in controlled environments, including high temperature, high humidity, and vibration/shock tests while the device is powered. The goal is to simulate conditions that could lead to the imminent failure of a new product. During testing, the product is monitored in the simulated environment. Environmental testing of electronics normally involves performing tests in a small environmental chamber.
Product engineers are sometimes reluctant to accept HALT/HASS results because the stresses placed on the system may be over-spec. In other words, they may exceed those found in the product’s envisioned environment. This has caused many engineers to refuse to fix known problems identified in HALT/HASS tests, only to have these same problems cause product failure later. An experienced CM can often identify simple design and assembly changes that can drastically extend the lifetime of your new product.
Humidity and Corrosion
Many PCBs will be deployed in a humid environment, thus a common test for PCB reliability is a water absorption test. In this type of test, a PCB is weighed before and after being put in an environmental chamber with controlled humidity. Any water that adsorbs onto the board will increase the board’s weight, and any significant change in weight results in disqualification.
When these tests are performed during operation, the exposed conductors should not corrode in a humid environment. When brought up to some potential, copper can easily oxidize, which is why exposed copper is normally plated with an oxidation-resistant alloy. Some examples include ENIG, ENIPIG, HASL, nickel-gold, and nickel.
The slight discoloration is due to corrosion during the environmental testing of electronics.
Thermal Shock and Cycling
Thermal testing is normally performed separately from humidity testing. These tests involve repeatedly changing the board temperature and examining how thermal expansion/contraction affect reliability. In thermal shock testing, the board is rapidly moved between two extreme temperatures using a 2-chamber system. The cold temperature is usually somewhere below freezing, and the high temperature is normally above the glass transition temperature for the substrate (above ~130 °C). Thermal cycling is performed using a single chamber, and the temperature is changed by several from one extreme to the other at 10 °C per minute.
In both tests, the board will expand or contract as the board’s temperature changes. During expansion, high stress will be placed on the conductors and solder points, which accelerates the lifetime of the product and allows mechanical failure points to be identified.
Burn-in testing involves applying extreme voltages and temperatures to components for an extended period. This is intended to detect early component failures, thereby increasing the reliability of any design built from the tested components. This requires plotting component failure rate over time, which forms a bathtub-shaped curve. Burn-in is the accepted practice for detecting early component failures using an expected extreme operating condition. This testing regime typically lasts from 48 to 168 hours.
Vibration testing setups can be quite expensive, and the costs only increase if you are looking for low frequency/amplitude vibration testing. High volume production for automotive, aerospace, or industrial equipment can benefit from vibration testing. Given the high costs of this equipment, not all CMs will have such capabilities. However, an experienced low-volume CM can provide a referral to a larger manufacturer that may be willing to perform these tests. The initial investment in testing can be significant, but the insights they provide can extend a product’s lifetime by a factor of 10.
At VSE, we’ve built a network of compliant laminate suppliers, allowing us to be cost-competitive and give customers assurance that their boards will pass the most advanced test. While we take environmental testing of electronics very seriously, we also fully test your board’s electrical functionality during fabrication with our proprietary test methodology. Whether you need quick turnaround PCB assembly services for a single piece or you are ready to produce at scale, we can expertly build your next PCBA.