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How Does Rework Factor Affect PCB SMT Processes?

Rework Factor Affect PCB SMT Processes

Rework factor is a measurement of how many defects are present on a production line. It is determined by calculating the First Pass Yield and dividing it by the average repair time per SMT defect. The results of this calculation give the percentage of defective boards that need rework and a rough estimation of the total rework cost.

The rework process is complex and requires specialized skills to perform well. It involves de-soldering or re-soldering on the surface and through-hole components of a printed circuit board (PCB). Whether it is to correct a manufacturing error, to repair a damaged product, or to change design specifications, rework of a pcb smt assembly can be challenging.

During the manufacturing of electronic equipment, the initial step is to place all the individual component pieces onto a pre-printed PCB. This is called component placement and it is a critical step that requires precision and accuracy. Various tools are used to ensure the correct placement of each part. For example, a stencil with apertures is used to guide the solder balls to the correct device pads. Then a high-speed pick-and-place machine uses a vacuum or gripper nozzle to remove the component from its packaging and place it onto the PCB. Some machines can place up to 80,000 individual components per hour.

How Does Rework Factor Affect PCB SMT Processes?

Once the component placement is complete, the PCB goes through a number of inspections and testing to verify that all of the parts have been placed correctly. For example, an AOI (automated optical inspection) machine checks that the parts are present, their type and value and that they are in the correct polarity. These inspections are a vital part of the overall quality control of the equipment.

After the final AOI check, the production line can proceed to the next phase of the manufacturing process: reflow soldering. This is a heating process that melts the solder and brings it to its proper state. The reflow temperature is carefully controlled to ensure that the solder does not oxidize or degrade. A well-performing reflow process is crucial to a product’s long lifespan and durability.

While it is not realistic to expect a zero-defect process, it is possible to significantly reduce rework and scrap rates. A good start is to improve the quality of the initial component placement. In addition, a BGA rework station that is equipped with the right nozzles can greatly improve rework performance and efficiency.

Ultimately, the key to successful rework is a close collaboration between the rework and failure analysis teams. It is important to close the feedback loop between these groups to avoid mistakes that lead to field failures. This includes a clear understanding of the effects of different rework chemistries on the electrochemical reliability of reworkd joints.

Whether it is a result of the wrong flux sneaking into the operation, underprocessed residues left on the reworked surfaces or improper residue removal, bad rework chemistry has a huge impact on field failures. Even a single corroded solder joint can ruin a product. Therefore, it is essential that these problems are identified and fixed at the rework process stage.


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