1. Why does the BGA solder mask of the PCB board need to plug holes? What are the acceptance criteria?

　　Answer: First of all, the purpose of soldering the plug hole is to protect the service life of the via hole, because the hole diameter of the plug hole required for the BGA position is generally relatively small, between 0.2-0.35mm, and some potions in the hole are not easily removed during post-processing Drying or evaporating, it is easy to leave residues. If the solder mask is not plugged or the plug is not full, there will be residual foreign bodies or tin beads in the post-process processing such as tin spraying and immersion gold, and components will be mounted on the customer. When heated at high temperature, foreign matter or tin beads in the hole will flow out and adhere to the component, causing defects in component performance, such as open and short circuit. BGA is located in the solder mask hole A, it must be fully filled B, there should be no redness or false copper exposure C, it should not be too full and the protrusion should be higher than the pad to be soldered next to it (it will affect the component mounting Effect).

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

　　Answer: The table glass of the exposure machine will not produce light refraction when the light passes through. If the reflector of the exposure lamp is flat and smooth, then when the light hits it, according to the principle of light, it forms only one reflected light on the board to be exposed. In principle, the light that hits the concave and the light that hits the convex will form countless scattered rays, forming irregular but uniform light on the board to be exposed, improving the effect of exposure.

　　3. What is side development? What kind of quality consequences are caused by the side development?

　　Answer: The bottom width area of the part where the unilateral green oil of the solder mask opening window is developed is called side development. When the side development is too large, it means that the area of the green oil that is developed to be in contact with the substrate or the copper skin is larger, and the greater the degree of suspension it forms, in the post-process processing such as: spray tin, immersion tin , Immersion gold and other side developing parts will form oil loss when they are attacked by high temperature, pressure and some potions that are more aggressive to green oil. will cause a bridge short circuit.

　　4. What is poor solder mask exposure? What quality consequences will it have?

　　Answer: After being processed by the solder mask process, the pads for mounting components in the post-process or the places to be soldered are exposed. During the solder mask alignment/exposure process, due to the problem of the light shield or the exposure energy and operation, the The outside or all of the green oil covered by this part is exposed to light, and a cross-linking reaction occurs. During development, the green oil in this part will not be dissolved by the solution, and the outside or all of the part of the pad to be soldered cannot be exposed, which is called soldering. Poor exposure. Poor exposure in the post-processing process will lead to inability to mount components, poor soldering, and severe open circuits.

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