Micro-Slicing And Drilling of Circuit Boards (1)

Micro-Slicing And Drilling of Circuit Boards

1 Overview

The quality of the circuit board, the occurrence and solution of problems, and the improvement of the manufacturing process all require microsectioning as the basis for observation, research and judgment. Whether it is correct or not is very relevant. A general production line is a large number of slices made by quality monitoring (monitoring) or quality control at the time of shipment to ensure quality. Because it is driven out in a hurry and inexperienced, it can only see the truth at most 60% to 70%. Some people can’t even see half of the truth without guidance and comparison. What can be seen in a blurred and ambiguous image? What’s the point of such a slice? If it’s just for business, it’s not a problem. If you really want to do a good job in quality and thoroughly identify and solve problems, you must carefully cut, grind, toss, and bite to get clear and visible micro-slices without causing any damage or misjudgment.

2. Classification

Anatomically destructive sectioning of printed circuit boards can be broadly divided into three categories:

(1) General Slicing (Microslicing)

It is a common practice to fill the through-hole area and other areas of the board with a vertical section, or to do a horizontal section for the through-hole.

(2) Cut Holes
Carefully cut a row of through-holes in half from the center with a diamond saw blade, or grind a row of through-holes in half with sandpaper, and place the half-cut through-holes without glue on a 20x-40x stereo microscope (or entity). Observe the whole situation of the half hole wall under the microscope. At this time, if the back of the through hole is also ground to be very thin, the substrate will be transparent, and the back light method can be used to check the copper layer of the hole.

(3) Oblique Section (45° or 30°)
It is possible to make a 45° oblique cut between the layers of the multi-layer board surface area or the through hole area, and then observe the situation between the conductors on the 45° section with a solid microscope.

3. Production Skills
Except for the second type of hole cutting method, which is used to observe the original surface condition of half of the hole wall, the other first and third types take the final careful polishing to see various real situations. This point is the key to the success or failure of slicing. This point is extremely important and should not be taken lightly. The following are the highlights of the production process.

3.1 Sampling:

Use a special cutting die to sample from any part of the board or use a shearing machine to cut the sample. Be careful not to approach the edge of the hole too much to prevent the through hole from being deformed by tension. You should also pay attention to the sampling method. It is best to cut it first, then Use a diamond saw blade to cut the desired cut sample to reduce the trouble of mechanical stress.

3.2 Sealing

The purpose of the sealant is to fill the through hole, fix and clamp the wall of the hole to be observed, so that it will not be dragged and extended and distorted during grinding. It is appropriate to use sealing glue, but the price is very expensive. Other types can be used, but the ones with good transparency, high hardness and few air bubbles are better. For example, black epoxy resin used for sealing small parts, toothpaste-like two-liquid epoxy resin sealant, Nanbao resin, and even green paint can also be used. Pay attention to reducing air bubbles. In order to make the hardening completely, oven catalysis is needed for quick reaction.

In order to facilitate the sealing of the cut samples, the formal method is to use a rolling spring clamp to clamp the samples so that they can be kept upright during sealing. The sealant for formal slicing is poured into a cylindrical blue rubber mold. After hardening, the sample cylinder can be easily pushed out by pushing the rubber mold, which is very convenient. This kind of special rubber mold is also a product of Buhler and is not easy to buy in China. Generally, the more troublesome and simple methods are:

3.2.1 Spray the mold release agent on the inner wall of the sawn short aluminum tube, stand the sample upright on the glass plate with double-sided tape, and then put the aluminum tube around the sample, so that the lower edge of the tube is close to the surface of the glass plate. It can be combined to prevent the glue from leaking out. After hardening, the cylinder can be taken out or a funnel-shaped mold with inclined walls can be used for easier demoulding.

3.2.2 Use rubber powder in the hot pressing mold to fill the through holes with increasing pressure and at the same time harden into a solid body. Among all kinds of sliced circles, this is the most beautiful.

3.2.3 Multiple slices are strung together with steel tips, in a special mold, multiple slices are filled with liquid glue at the same time, and multiple slices can be ground at the same time, which is called the Nelson-Zimmer method, which can grind nine cylinders at the same time, and as many as 5.6 slices can be packed into one cylinder, which is a lot of practice.

3.2.4 Use a ready-made acrylic mold, place the sample, and seal it.

3.2.5 The easiest way is to apply the colloid on the PE paper, so that each through hole on the cut sample is slowly scraped through the glue surface, forcing the glue to squeeze into the hole, and then insert into the slot of the wooden board, and concentrate the oven to make it hard, you can also use green paint to fill the glue.

3.2.6 A small amount of cut samples can be directly filled with glue at the hole with bamboo sticks, and then baked upright to harden. The last two kinds of colloids are very small, so the grinding time can be saved, but to maintain the level of the grinding surface, it is necessary to work hard, but good slices are made by this simple method.