PCB News - Understanding PCB micro-sectioning

Microsectioning is an extremely important link in the process of PCB manufacturing. It is an important means to detect PCB circuit boards, find and solve problems, ensure the quality of the board, improve the yield of products, and improve the process and production process.

Micro-sectioning provides an important objective factual basis for discovering and solving problems. The correct production of micro-slices is related to whether the truth of the problem can be found, whether the PCB manufacturing process and production process can be improved, and the problem can be avoided again.

To find the truth, solve problems, and continuously improve the production process or production process, we must first understand and understand micro-sectioning. Really and correctly master the production method of microsections, so as not to be misled by some illusions.

Second, the classification of micro-slices in PCB manufacturing

Circuit board anatomical destructive microsection methods can be roughly divided into three categories:

1. Microsection

Refers to the through-hole area or other plate area, after the cut sample is filled with sealant, the vertical section is made perpendicular to the board surface direction, or the horizontal section of the through hole is made cross-section (Horizontal section), These two methods are generally common micro-sectioning.

PCB longitudinal section microsection

2. Micro-cut holes

It is to carefully use a diamond saw blade to cut a row of through holes from the center into two halves, or use sandpaper to grind a row of through holes in half vertically and longitudinally. Under a 20X~40X stereo microscope (or called a solid microscope), observe the overall condition of the remaining half wall in a full field of view. At this time, if the back plate of the through hole is also ground to be very thin, the half hole of the translucent substrate can also be back lighted to check the coverage of the copper layer of the initial hole.

PCB micro-cut holes under a stereo microscope

PCB back cut hole

Cut the cavity with a diamond blade, and the two halves will immediately appear under the sun, and any PCB production defects will be invisible to the original appearance. If you want to learn more about the details, you can do technical and academic micro-sections. Direct observation with a stereo microscope after cutting a hole is more holistic than micro-sectioning, but photography requires the help of an electron microscope SEM to have a better effect.

3. Oblique slice

Fill the through holes of the multi-layer PCB board with glue, and perform oblique grinding of 45° or 30° in the vertical direction, and then observe the variation of the conductor lines on the oblique plane with a solid microscope or a high-power tomography microscope. In this way, the dual characteristics of straight cut and cross cut can be taken into account. However, this method of slicing has a certain degree of difficulty, and it is not easy to perform microscopic observation.