PCBA Tech - Four inspection routine requirements for SMT patch products

At present, in electronic products, security products, medical treatment, industrial control and other fields that need PCBA, product requirements are getting higher and higher, the components on the circuit board are also more precise, and the package is smaller, so the PCBA engineers have organized a I share with you all the required documents for product inspection, and I hope to help you:

1. Quality requirements of solder paste printing process:

1. The amount of printed solder paste should be moderate, and it can be pasted well, and there is no phenomenon of too much solder paste or too much solder paste;

2. The position of the solder paste is centered, without obvious deviation, and the paste and soldering effect should not be affected;

3. The solder paste dots are well formed, the solder dots are full and smooth, and there is no continuous tin or uneven state.

2. PCBA electronic components soldering process requirements:

1. The surface of the FPC board should be free of solder paste, foreign objects and spots that affect the appearance;

2. The bonding position of PCBA electronic components should be free of rosin or flux and foreign objects that affect the appearance and soldering tin;

3. The tin spots under the PCBA electronic components are well formed, and there is no abnormal wire drawing or sharpening.

Third, the quality requirements of PCBA electronic component mounting process:

1. The placement of PCBA electronic components must be neat, centered, without offset or skew;

2. The type and specification of the components at the mounting position should be correct, and the components should be free of missing, wrong or reverse pasting;

3. SMD devices with polarity requirements need to be installed according to the correct polarity mark;

4. There should be no residual tin beads and tin dross on the pads of multi-pin devices or adjacent components.

Fourth, PCBA electronic components appearance process requirements:

1. There should be no cracks or cuts on the bottom of the board, surface, copper foil, lines, through holes, etc., and no short circuit caused by poor cutting;

2. The FPC board should have no leakage V/V deviation, and be parallel to the plane, and the board should have no bulging deformation or expansion and blistering;

3. There is no blurring, offset, reverse printing, printing deviation, ghosting, etc. of the silk-screened characters of the marked information;

4. The aperture size required for SMT patch processing meets the design requirements, and is reasonable and beautiful.

What is the surface mount wetting process of SMT chip processing plant?

It refers to the phenomenon that the molten solder spreads and covers the surface of the metal to be welded during welding.

Wetting means that dissolution and diffusion have occurred between the surfaces of the liquid solder, forming an intermetallic compound (IMC), which is a sign of good soldering.

When a solid metal sheet is immersed in the liquid solder tank, there is contact between the metal sheet and the liquid solder, but this does not mean that the metal sheet has been wetted by the liquid solder, because there may be a barrier between them. Pull small pieces of metal out of the solder bath to see if they are wet.

The wetting of the SMT chip processing plant only occurs when the liquid solder is in close contact with the surface of the metal to be welded, and then sufficient attractiveness can be ensured. If there are any firmly attached contaminants on the surface to be welded, such as oxide film, it will become a metal connection barrier and prevent wetting. On the contaminated surface, the performance of a drop of solder is the same as the performance of a drop of water on a greased plate, it cannot be spread, and the contact angle θ is greater than 90°.

If the surface to be soldered is clean, then their metal atoms are located close to the interface, so wetting occurs, and the solder will spread on the contacting surface. At this time, the solder and the basic atoms are very close, so an alloy is formed at the interface that attracts each other, ensuring good electrical contact and adhesion.

The solderability of SMT chip processing plants refers to the ability of the base material to be soldered to be soldered under a specified time and temperature. It is related to the thermal container, heating temperature and surface cleanliness of the soldered target material (component or PCB pad).