PCBA products in SMT processing matters needing attention

First, when smt patch processing, we all know that we need to use solder paste. For the solder paste just bought, if it is not used immediately, it must be placed in the environment of 5-10 degrees for storage, in order not to affect the use of the solder paste, must not be placed in the environment below zero, if higher than 10 degrees is not possible.

2. When smt production and mounting process is carried out, the equipment of the smt machine must be inspected frequently. If the equipment is aging or some zero components are damaged, the equipment must be repaired or replaced with new equipment in order to ensure that the SMT patch processing and welding will not be skewed and high material throwing occurs. Only in this way can we reduce production costs and improve production efficiency.

3. When smt patch processing plant is carried out, if the welding quality of PCB board is to be guaranteed, it is necessary to always pay attention to whether the setting of reflow welding process parameters is very reasonable. If the parameter setting is wrong, the welding quality of PCB board cannot be guaranteed. Therefore, under normal circumstances, the furnace temperature must be tested twice a day, and the minimum must be tested once. Only by constantly improving the temperature curve and setting the temperature curve of welding products, can we ensure the quality of processed products.

It can be said that the technical content of small batch smt plant is very high. We must pay attention to the above points in the process of processing. If we do not pay attention to these points and blindly want to improve production efficiency, the quality of processed products will have problems, and the sales of products will be greatly affected.

2. Solutions to the tablet component stele phenomenon

Cause of formation:

(1) The melting time of the solder paste at both ends of the components is not synchronized or the surface tension is different, such as poor printing of the solder paste (one end is incomplete), biased paste, and the size of the solder end of the components is different. Usually the melted end of the solder paste is pulled up.

(2) pad design: pad extension length has a suitable range, too short or too long are prone to stele phenomenon.

(3) If the welding paste is too thick, the components will float after melting. In this case, the components are easy to stand because of hot air blowing phenomenon.

(4) Setting of temperature curve: the monument generally occurs at the moment when the solder joint begins to melt, and the heating rate near the melting point is very important. The slower it is, the more conducive to eliminating the monument phenomenon.

(5) One welding end of the component is oxidized or contaminated and cannot be wet. Special attention should be paid to components with single-layer silver welding ends.

(6) the pad is contaminated (there is silk screen printing, solder resistance ink, adhesion of foreign bodies, is oxidized).

The formation mechanism:

During reflow welding, the heating of the chip components is heated at the same time. Generally speaking, the pad with the largest exposed area is first heated to a temperature above the melting point of the paste. In this way, one end of the component is often pulled up by the surface tension of the solder at the other end.

The solution:

(1) Design

Reasonable design of the pad - the extension size must be reasonable, as far as possible to avoid the extension length of the outer edge of the pad (straight) wetting Angle is greater than 45°.

(2) Production site

1. Frequently wipe the net to ensure that the welding paste results are complete.

2. The position of the patch is accurate.

3. Use non-eutectic solder paste and reduce the temperature rise during reflow welding (controlled under 2.2℃/s).

4. Reduce the thickness of welding paste.

(3) Incoming materials

Strictly control the quality of incoming materials to ensure that the effective area size of both ends of the components used is the same (the basis of surface tension).

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