SMT process specifications and common anomalies

The SMT process specification is the surface mount technology, which is the standardized requirement inPCB assembly process and a vital basis for ensuring product quality.

What are the SMT process specifications?

1) Equipment specifications

Placement machine: the model, specifications, performance, and usage methods must meet specifications.

SMT Reflow oven: reflow oven’s model, specifications, performance, usage methods, etc.

Visual inspection equipment: model, specifications, performance, and usage methods must meet specifications.

Automated testing equipment: models, performance, and usage methods must conform to the standard.

2) Material specifications

Solder paste: solder paste model, specifications, performance, usage methods, etc.

Components: component model, specifications, performance, and usage methods should meet standard

PCB: PCB model, specifications, performance, usage methods, etc.

3) Process specifications

Solder paste printing process: steps, parameters, precautions, etc. of solder paste printing.

SMT process: SMT steps, parameters, precautions, etc.

Reflow process: reflow steps, parameters, precautions, etc.

4) Inspection specifications

Visual inspection: methods, standards, frequency, etc. of visual inspection.

Automated testing: methods, standards, frequency, etc. of automated testing.

Common Abnormalities of SMT

SMT process anomalies such as solder beads, tombstones, bridging, and rejection can lead to product quality issues.

1) Solder beads

Solder beads are one of the common anomalies in the SMT process.

It is some small particles of solder around the pad. The main reasons for the formation of solder beads include:

• Improper selection of solder paste.

• The steel plate opening is not suitable.

• The mounting pressure is too high.

• Improperly the furnace temperature curve.

2) Erect a monument

It appears as a rectangular chip component with one end soldered to the pad and the other sticking up.

• The main reasons for erecting a monument include:

• Uneven thermal performance.

• Uneven solderability of components or PCB pads.

• Mounting offset.

The generation of tombstones will lead to poor product appearance and even affect the product function.

Therefore, we need to take measures to prevent the occurrence of tombstones.

3) Bridging

The solder joints are connected by solder, causing a short circuit. The causes of bridging include:

• The opening of the steel mesh is not appropriate.

• Too much solder paste.

• Solder paste collapse.

• The reflow time is too slow.

• The contact pressure between components and solder paste is too great.

4) Incoming material rejection

Incoming material rejection is one of the common anomalies in SMT.

It is the failure of components or PCB pads to form a good connection with the solder. The main reasons include:

• Oxidation of components or PCB pads.

• Surface defects of components or PCB pads.

• Manufacturing process problems of components or PCB pads.

In addition to the common anomalies mentioned above, other anomalies may occur in the SMT process, such as component lift, component shift, missing, etc.

These anomalies can also lead to product quality issues and should discovered and handled on time.

Summarize

SMT process anomalies such as solder beads, tombstones, bridging, and rejection can lead to product quality issues.

In order to prevent product quality problems, it is necessary to manage SMT processes. Strictly implement these specifications, strengthen the management of equipment, materials, and inspections, and thus reduce the occurrence of product quality problems. At the same time, PCB manufacturers must continue to create new technologies to speed up PCB assembly.