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Technical Article

What Inspections Need To Be Done Before SMT Assembly?

Time:2021-02-24 11:46:00 Click:

1. SMT Components Inspection


The main inspection items of components include: Solderability, pin coplanarity and usability, which should be sampled by the inspection department. To test the solderability of components, stainless steel tweezers can hold the component body and immerse it in a tin pot at 235±5℃ or 230±5℃, and take it out at 2±0.2s or 3±0.5s. Check the soldering condition of the soldering end under a 20 times microscope, and which is still required that more than 90% of the soldering end of the component should be soldered.





Meanwhile, the following visual inspections can be done in SMT factory:

1> Visually or with a magnifying glass, check the solder ends or pin surfaces of the components for oxidation or contamination.

2>The nominal value, specification, model, accuracy, and external dimensions of the components should be consistent with the product process requirements.

3> The pins of SOT and SOIC cannot be deformed. For multi-lead QFP devices with a lead pitch of less than 0.65mm, the pin coplanarity should be less than 0.1mm (optical inspection by the placement machine).

4>For products that require cleaning for SMT Assembly, the mark of the components will not fall off after cleaning or the performance and reliability of the components (visual inspection after cleaning).





2. Printed Circuit Board (PCB) Inspection


1> The PCB land pattern and size, solder mask, silk screen, and via hole settings should meet the design requirements of SMT Printed Circuit Boards. (Eg. Check whether the pads spacing is reasonable, whether the screen is printed on the pads, whether the via is made on the pads, etc.).

2>The external dimensions of the PCB should be consistent, and the external dimensions, positioning holes, and reference marks of the PCB should meet the requirements of the production line equipment.


3> PCB allowable warpage size:


        Upward/convex surface: maximum 0.2mm/5Omm length and maximum 0.5mm/the length of the whole PCB.

       Downward/concave surface: maximum 0.2mm/5Omm length and maximum 1.5mm/the length of the whole PCB.


4>Check whether the PCB is contaminated or damp.





3. SMT Assembly Matters Need Attention


1> Before plug-in, the SMT Assembly technician wears an effective electrostatic ring to check that the electronic components of each order are free of errors/mixtures, damage, deformation, scratches, etc.

2>The plug-in board of the circuit board need to prepare the electronic materials in advance, and pay attention to the correct polarity of the capacitor.

3> After the SMT printing operation is completed, check for defective products such as no missing insertion, reverse insertion, misalignment, etc. And then flow the good tin finished products into the next process.


4>Before starting SMT Assembly, wear an electrostatic ring. The metal sheet should be close to the skin of the wrist and be well grounded. Work alternately with both hands.

5>Metal components such as USB/IF socket/shielding cover/tuner/network port terminal must wear finger cots when plugging in.

6>The position and direction of the inserted components must be correct, the components should be flat against the board surface, and the elevated components must be inserted at the K foot position.





7>If any material is found to be inconsistent with the specifications on the SOP and BOM, it must be reported to the shift/group leader in time.

8>The material should be handled with care. Do not drop the PCB board that has passed the previous process of SMT and cause damage to the components. The crystal oscillator should not be used.

9>Please tidy and keep the work surface clean before going to get off work.

10>Strictly abide by the operating rules of the work area. Products in the first inspection area, to-be-inspected area, defective area, maintenance area, and low material area are strictly prohibited to be placed at will.


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