How to detect and solve PCB short circuit problem

I think a lot of people have experienced the short circuit. Once the short circuit occurs, the effect of the line has a great impact on our equipment. If the core component of the electronic device has a short circuit problem, this is a devastating blow to the product, and any engineer is unwilling to encounter such a problem. So what should we do when the circuit board has a short circuit? Leadsintec PCB engineers take everyone to understand.

The reasons and solutions of PCB short circuit board

Short circuit caused by PCB design problem

1. The biggest reason for PCB short circuit is improper pad design.

Solution: The circular pad can be changed to an oval shape to increase the distance between the point and the point, which can prevent short circuits.

2. Inappropriate design of PCB board parts will also lead to short circuit boards, resulting in unevenness. If SOIC’s feet are parallel to Xibo, it is easy to cause short -circuit accidents.

Solution: The direction of the part can be changed to tin wave.

3. There is another reason for the short circuit of the PCB board, that is, the automatic bending of the plug. Because the length of the IPC regulations is less than 2mm, when the angle of curvature is too large, the parts are too large, which can easily cause short circuits.

Solution: The welding point is more than 2mm from the line.

Short circuit caused by PCB production problem

1. Scratching short circuit

1. After coating the wet film, cracking, and improper operation cause the membrane surface to crack.

2. The output of the display machine cannot be busy and may cause a collision between the panel and the panel.

3. Improper use of the plate during electroplating, improper operation on the splint, improper operation when handling the plate in front of the manual line, etc.

The improvement method is as follows:

(1) It is easy to scratch because it is easy to scratch when the wet film is coated, so the interval between the board and the plate is a little far away to ensure that there are no scratches on the surface of the board. Take your hands and place the board with both hands and strictly avoid overlaying with the board and the plate, or friction between the board and the counter to avoid scratching the board.

(2) Adjust the spacing between the plates according to the size of the plate and the operating capacity of the connected plate. The time machine of the unmanned board shall not be placed on the board. Collisions between plates cause the surface of the plate to crack.

(3) Take your hands and place the board with both hands while electroplating to avoid stacking two or more plates for splints. Avoid friction between the board and the countertop when manually wiring. When the plate is a clip, a clip to the ground to avoid collision.

Second, short circuit

1. The anti-coating layer is too thin. During electroplating, the coating passes through the membrane, and the clamping membrane is formed. Especially the smaller the spacing of the wire, the more likely it will cause short circuits.

2. The graphic distribution of the board is uneven. During the patterning process, the insulating lines are due to the high potential and the coating is beyond the thick film, which forms a short circuit.

The improvement method is as follows:

(1) Increase the thickness of the anti-plating layer: Select the dry film with a suitable thickness. If it is a wet film, it can be printed with a low net version of the number of mesh, or it can increase the film thickness by printing two wet films.

(2) The distribution of the plates is unevenly distributed, and the current density (1.0 ~ 1.5A) can be appropriately reduced. In daily production, we need to ensure the reasons for the yield, so the control of the electroplating time is usually shorter, the better, so the current density used is generally between 1.7 and 2.4A. The density will be 1.5 to 3.0 times in the normal area, which often causes the height of the plating height of the plating height in the upper distance in the isolated area to be much higher than the thickness of the membrane. As a result, the clamps are short-circuited, and at the same time the weld thickness on the line will be thin.

Third, short circuits caused by running time

1. Inappropriate operation in the lowered position causes the tin to fall;

2. The retired board is superimposed together to increase running time.

The improvement method is as follows:

(1) The concentration of the decreasing portion is high, the withdrawal time is long, the anti-coating has already fallen, and the plate can still be soaked in the strong alkali solution. Some tin powder is attached to the surface of the copper foil. On the copper surface, it plays a role in corrosion, resulting in the removal of non-removing copper, resulting in a short circuit of the line. Therefore, we must strictly control the concentration, temperature, and decay time of the decay part. At the same time, use the plug-in shelf to insert it when the back is retracted, and the board cannot be stacked together.

(2) The retired plate is superimposed together without drying, so that the tin between the plate and the plate is immersed in an undulating degraded solution. Some tin layers will dissolve on the surface of the copper foil. The very thin metal tin protects the copper surface, which plays a role in corrosion, causing the copper to be removed, which will cause a short circuit of the line.

Various short circuit characteristics of PCB board

Short circuit boards are a very common problem in the production of circuit boards. There are usually two short circuits. One is that the PCB board has reached a certain period of use. The second situation is that the inspection work in PCB circuit board production is not in place. However, these small errors in production can cause components to burn, and the damage to the entire PCB board is very large, which is likely to cause scrap. Different types of short circuit characteristics are also different.

(1) Base Corporal short circuit

It is characterized by the formation of short-circuit copper surfaces between the two lines, which is significantly lower than the copper surface of the line. It can be a single short circuit or a large number of short circuits. The reason for the formation is that in the etching degradation process, the dry film is not completely faded or because the dry film dandruff is pasted on the surface of the plate, it causes the base copies to not be eroded during etching.

(2) Plating short circuit

The characteristics are that the copper surface of the short circuit and the copper surface of the line are equivalent. It may appear in a separate short circuit, or it may also appear with a large number of short circuits. The reason for the formation is that the dry membrane is broken during too long electroplating or stirring of the solution, and copper and tin lead alloys are plated in the area covered by the dry membrane. After the etching process, a short circuit is formed.

(3) Short circuit

It is characterized by a short circuit between the two wires, and the width of the thin wire is 0.025~0.075mm. As long as the cause is not well controlled during the exposure, hairline or other small fibers fall on the plate surface, causing small dry membranes during the exposure to not be exposed, and short circuits are formed after the electroplating time is completed. Short-circuit short circuits may also be duplicate short circuits. But there will be no more, because the production department will clean the exposure glass for each exposure.

(4) Short-circuit

It is characterized by a small concave pit in the formation of line defects, and this short circuit is caused by small concave pits. The reason is that when the multilayer plate is pressed, there are pits or substrate materials. Due to the presence of the pit, there is a gap between the dry film and the copper surface when applying the dry film. Therefore, after being plated, a short circuit phenomenon is formed after etching.

(5) Insufficient etching

Typically, more or less copper-like copper-like copper-free areas are small. The thickness is small. When observing the line area, the short circuit formed is relatively long, which is continuous. The surface is low because the position concentration is too low, the setting speed is too fast and the time is too short.

(6) Short Circuit Scraping

It is characterized by shorter circuits along a copper line (not necessarily a straight line). Short circuits are also caused by this copper wire, and scratches along a certain direction. The reason is that after exposure, the dry film is scratched or scratched for mechanical or artificial reasons before electroplating (it can still be returned before plating), and a short circuit is formed after electroplating and etching.

PCB circuit board short circuit inspection method

1. Check the PCB board again before manual welding, and check whether the key circuit is short-circuited with a multimeter; then, after each welding, use a multimeter to test whether the power and ground are short circuits.

2. Pay attention to small table stickers during welding, especially the power filter capacitor, which can easily cause power and ground short circuit.

3. If there is a BGA chip, it is best to divide the power supply of each chip during design and connect it with a magnetic bead or 0 Euro resistance. It is worth noting that, because BGA welding is difficult, if it is not automatic welding, it is easy to short circuit the adjacent power supply and the two welding balls.

4. Open the PCB diagram on the computer, turn on the short circuit network, and see which places are most recently connected to one.

5. Once a short circuit is found, you can take a plate for cutting the cable, and then power on each part of the function block, and slowly eliminate the failure. This method is suitable for single/double-layer boards.

6. Use a short-circuit positioning analyzer for detection, which is also an effective method.