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Some common problems of PCB
Views:640 Time:2022-10-24

1. Why should holes be plugged when BGA position is in resistance welding? What is the acceptance standard?

First of all, the solder plug hole is to protect the service life of the vias. Because the hole diameter of the plug required for the BGA position is generally small, between 0.2 and 0.35mm, some of the liquid medicine in the hole is not easy to be dried or evaporated during the post process processing, and it is easy to leave residue. If the solder plug hole is not plugged or the plug is not full, there will be residual foreign matters or tin beads during the post process processing, such as tin spraying and gold deposition. Once the customer installs the components and welds at high temperature, Foreign matters or tin beads in the hole will flow out and stick to the element, causing defects in element performance, such as open circuit and short circuit. The BGA position is in the solder plug hole A, must be full B, no redness or false copper exposure is allowed, and no too full protrusion is allowed to be higher than the pad to be welded beside (which will affect the effect of component mounting).

 

2. What is the difference between the table glass of the exposure machine and ordinary glass? Why is the reflector of the exposure lamp concave and uneven?

The table glass of the exposure machine will not produce light refraction when the light shines through. If the reflector of the exposure lamp is flat and smooth, when the light shines on it, according to the principle of light, it forms only one reflected light to shine on the board to be exposed. If the concave is uneven, according to the principle of light, the light shining on the concave and the light shining on the convex will form countless scattered lights, forming an irregular but uniform light to shine on the board to be exposed, so as to improve the exposure effect.

 

3. What is side development? What are the quality consequences of excessive side development?

The bottom width area of the developed part of the green oil on one side of the resistance welding window is called side development. When the side development is too large, it means that the greater the green oil area of the developed part in contact with the substrate or copper skin, the greater the degree of suspension it forms. When the side development part is attacked by high temperature, pressure and some potions that are more aggressive to the green oil in the later process processing, such as tin spraying, tin deposition, gold deposition, etc., it will form oil loss. If there is a green oil loss bridge in the IC position, The bridging short circuit will be caused when the customer installs the welding element.

 

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