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Common problem
Question

Why does tin spray cause surface irregularities?

Answer

Reason analysis: 1. The board is unevenly heated up and down, and the last in and first out are prone to the defects of the plate bending plate. 2. When the tin is in the furnace, the surface tension of the liquid tin on the pad will be arc-shaped, causing the tin on the pad. The thickness is uneven, and due to the blowing force of the hot air and the effect of gravity, the solder sag is generated at the lower edge of the pad, so that the soldering of the SMT surface mount component is not easily stabilized, and it is easy to cause offset or inscription of the post-weld part. Phenomenon tomb stoning; 3, the smaller the pad, the more obvious the arc of the pad surface, the worse the flatness. Solution: For BGA package boards with less than 14 MIL pads or boards with high flatness requirements, consider the hidden dangers of tin spray. It is not recommended to make tin-plated plates. It can be changed to immersion gold and gold plating. If the customer must make it Tin plate, the customer's requirements for flatness must be clarified.

Question

Warpage exceeds standard, affecting welding

Answer

Analysis of the reasons: 1. The interlayer core board and the prepreg are arranged asymmetrically; 2. The difference of the area of the two sides of the pattern is too large; 3. The blind buried hole design of the interlayer asymmetry, for example, the blind hole of the design 1-3 when the four layers are formed; Method: 1. Arrange the symmetrical design of the interlayer core board and the prepreg; 2. The area of the line pattern of the A side and the B side of the outer layer should be as close as possible. If the A side is a large copper surface, and the B side only takes a few lines, the printed board is easily warped after etching, and it is possible to add some independent meshes with the customer's suggestion; 3. Reduce the asymmetric blind buried hole the design of. At present, there are customer complaints that our warpage does not meet the standard, but the measured board is in compliance with the IPC standard. In the case of such cases, in order to avoid complaints arising from future non-conformity with the customer's standards, the sales must specify the customer's requirements for warpage when filling out the processing instructions. When designing the customer, try to make the structure of the blind hole symmetrical, so as to ensure the curvature of the finished board. If the design really can't be designed as a symmetrical structure, the standard of the slab needs to be relaxed.

Question

Through hole processing method analysis

Answer

The through hole processing method is divided into: through hole covering, through hole opening window, through hole plug hole, and through hole according to the original file of the customer. The via coverage covers the solder mask ink on the via pad, but solder mask ink is not guaranteed on the hole walls in the hole. The via opening window does not cover the solder resist ink on the via pad, and there is no solder resist ink on the hole wall in the hole. The via plug is covered with solder resist ink on the via pad and filled with solder resist ink in the hole. The vias are designed as “perforated windows” or “over-holes” in the customer's original file according to the customer's original file.

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