PCBA Tech - Common Faults and Solutions in SMT Chip Processing

In the process of SMT placement, some common failures will inevitably occur, leading to the occurrence of poor PCBA. What are the common faults and solutions of SMT chip processing?

1) Component displacement: after the adhesive is cured, the component is displaced, and in serious cases, the component pin is not on the bonding pad.

Cause: uneven adhesive output of patch adhesive; When mounting, the displacement of components or the initial adhesion force of the mounting adhesive is small; The PCB was placed for too long after dispensing, and the glue was semi cured.

Solution: Check whether the rubber nozzle is blocked, and eliminate the uneven rubber discharge; Adjust the working state of the mounter; Replace the patch adhesive; The PCB should not be placed for too long after dispensing.

2) Chip falling after wave soldering: after curing, the bonding strength of components is not enough, and sometimes chip falling occurs when touching with hands.

Cause: the parameters are not in place, especially the temperature is not enough; The size of components is too large and the heat absorption is large; The UV curing lamp is aging, and the amount of glue is insufficient; Components/PCB are polluted.

Solution: Adjust the curing curve, especially increase the curing temperature; In general, the peak curing temperature of thermosetting adhesives is critical. Observe whether the light curing lamp is aged and whether the lamp tube is blackened; Quantity of glue and whether components/PCB are polluted.

3) Floating/displacement of component pins after curing: the cured components will float or shift with adhesive, and the tin will enter under the bonding pad after wave soldering, resulting in short circuit and open circuit.

Cause: The patch adhesive is uneven, the amount of patch adhesive is too much, and the components are offset when mounting.

Solution: Adjust dispensing process parameters, control dispensing amount, and adjust patch process parameters.

Many process documents are required in the PCBA processing and production process, such as SMT mounting operation instructions, equipment operation procedures, plug-in operation instructions, repair welding operation instructions, program reading and writing operation instructions, inspection operation instructions, etc. So, how to define the SMT chip processing process file?

1. Definition of process documents

1) Process documents refer to detailed specifications for specific operation, packaging, inspection and circulation of equipment and products in a production or circulation link.

2) The process document is to express the procedures, methods, means and standards for organizing the production process in the form of words and charts.

3) All process plans, standards, schemes and quality control procedures prepared by the process department belong to the scope of process documents; Process documents are mandatory disciplinary documents, which must be written in a standardized form. No one is allowed to modify them at will. Violation of process documents is a disciplinary offence.

4) The process documents shall be correct, complete, unified and clear.

2. Role of process documents

1) Provide the production department with specified processes and procedures to facilitate the orderly production of products.

2) Propose technical requirements and operation methods for each process and post to ensure that operators can produce products meeting quality requirements.

3) Determine the man hour quota and material quota for the production planning department and the accounting department, and control the manufacturing cost and production efficiency of products.

4) Organize the PCBA process discipline management and staff management of the production department according to the document requirements.