PCB (Printed Circuit Board) is subject to various mechanical stresses during manufacturing, assembly and transportation. These stresses may cause problems such as solder joint cracking, circuit damage and substrate cracking, thereby affecting the reliability and service life of the product.

1. Specific causes and Impacts of PCB Strain Measurement

(1). Mechanical stress in the ‌manufacturing process: During stages such as SMT, DIP, assembly, and reliability testing, excessive mechanical stress can lead to problems like solder ball cracking, circuit damage, pad lifting, and substrate cracking. If these problems are not detected and dealt with in time, they may cause the product to malfunction during use. ‌

(2). Mechanical stress during assembly and transportation: During the processes of panel separation and assembly, PCBS are prone to mechanical stress, which can lead to solder joint cracking or delamination of the PCB. With the trend of thinner and lighter electronic products, the size of components has shrunk and the strength of solder joints has decreased, making them more sensitive to mechanical stress. ‌

(3). Application of new materials and new processes: The lead-free soldering process and the application of new laminating materials have changed the mechanical properties of PCBA, and strain testing is needed to verify process compatibility.

2. Methods and Standards for PCB Strain Measurement

(1)The main items that need to be prepared for PCBA stress testing include the following: ‌

 (a) strain gauge: Selecting the appropriate strain gauge is the key to conducting stress tests. Common strain gauges include single-axis, double-axis and triple-axis metal foil strain gauges, which are suitable for different testing requirements. The resistance value of the strain gauge is usually 120±0.5 ohms ‌.

 (b) Test equipment and instruments: It is necessary to prepare equipment such as the TSK-32/DL-1000 stress tester for connecting strain gauges and collecting data. Ensure that the instrument is configured correctly, including parameters such as sampling frequency, filter value, gain setting, etc. ‌.

(2). Specific operation steps for PCBA stress testing:

(a)Select test points: Choose stress-sensitive devices such as BGA, ceramic capacitors, etc., and determine the bonding position of the strain gauge ‌.

(b)Paste the strain gauge: Paste the strain gauge at the selected position, ensuring it is firmly adhered and accurately positioned ‌.

(c)Connect the instrument: Connect the guide wire of the strain gauge to the stress tester, and configure parameters such as sampling frequency and filter value ‌.

(d)Perform test actions: perform actions such as screwing, panel separation, and assembly on the fixture, and collect data ‌.

(e)issue report: Import the collected data into the software and generate a stress test report ‌according to the standards.

Through the above preparations and steps, PCBA stress testing can be effectively carried out to ensure the quality and reliability of the circuit board.

(3).standard specification: In accordance with the IPC/JEDEC-9704 standard, clearly define the data acquisition frequency for test point selection (it is recommended to be ≥500Hz) and the method for determining strain thresholds. ±500με (micro-strain) is usually taken as the reference threshold, and the threshold needs to be adjusted for different devices.

3.The Akemond strain measurement system is a professional stress-strain testing instrument designed for various PCBA manufacturing processes. It is highly suitable for customer R&D, electronic processing plants or laboratories to conduct strain analysis of defective products in various PCBA manufacturing processes. The main manufacturing processes include: PCBA board cutting and separation, SMT, FCT, ICT, fixture pressing, screw locking, drop, impact, transportation and other full-process strain tests.