Backlight experiment

Printed circuit board production is a complex, multi-level manufacturing process, and improper control during the production process may result in many scrapping and quality defects. Whether using traditional chemical copper PTH or new direct electroplating processes, the metallization of through and blind holes before electroplating is a complex operational process. To ensure the maximization of production line products, it is necessary to use reasonable testing methods and means to ensure the smooth and effective operation of the entire process. In addition, the confirmation and evaluation of the effectiveness of each processing step and each part in the control process are equally important.

The evaluation and monitoring of the deposition coverage rate of PTH process through holes is a very important quality control inspection, which can ensure that the coating after chemical deposition treatment can effectively provide the conductivity and other performance requirements of subsequent through holes, and can also timely detect some unpredictable problems in the production line.

Regular backlight and front light testing can monitor the quality and coverage of chemical copper deposition, and can prevent and effectively reduce adverse defects in the chemical copper plating process. Reasonable and effective backlight testing can effectively monitor and detect changes in product and overall copper coverage from PTH production lines.

Test sample inspection

The sample can be observed using a 50-200x magnifying glass or a metallographic microscope. First use the upper light to focus, then use the lower light to observe the backlight condition. The transparent area is the area with poor coverage of chemical copper deposition. To test each test hole of the sample. There are many evaluation criteria, and a testing standard range of 0.5 to 5.0 can be used. 5.0 represents complete chemical copper coverage. We use standard charts with some columns to effectively ensure consistency and stability in backlighting operations among different employees.

Sampling and inspecting the backlight of production line products can promptly identify potential quality issues with production line PTH. By monitoring the backlight coverage of the entire production line and the trend of gradual decrease in coverage over time, timely detection of tank liquid control problems or tank liquid lifespan can be achieved.

Picture：Microscope backlight image

In the backlight test, the backlight level of each hole on the test piece should be observed, evaluated, and recorded one by one based on the backlight level table. Once all test holes have undergone backlight checks, record the average backlight level and the lowest backlight level for each individual hole in the test hole. By recording data with the lowest backlight level, continuous stability of the chemical copper deposition coverage of the tested sample can be provided. First, use a backlight to observe the coverage of chemical copper in the hole, and then use a front light to check the deposition status of chemical copper in the hole and areas with poor or no copper deposition. To observe the deposition status of chemical copper, it is best to observe the relatively smooth transverse glass fiber bundle part inside the hole. The smooth surface of the transverse glass fiber bundle better reflects the deposition status of chemical copper than the relatively rough epoxy resin surface. Determine the copper free area inside the hole by repeatedly using the backlight and front light.