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How to check Printed Circuit Board Assembly

A wide variety of inspection equipment has been invented in order to fulfill the task of Printed Circuit Board Inspection. Automatic Optical Inspection (AOI) is mainly applied on the inner layer inspection before outer layer Printed Circuit Board being laminated onto it. After lamination, X-Ray monitoring system being used to inspect the preciseness of layer-to-layer alignment and minor defect; Laser scanning system can help to inspect PAD before reflow soldering. All the methods mention above plus visual inspection on-site as well as automatic pick & place machine can effectively ensure the stability of final assembly and PCBA.

However, final inspection upon Printed Circuit Board Assembly is indispensable even if all the efforts be made; maybe it is the most critical step because it is the final unit for product and process evaluation.

Final inspection of Printed Circuit Board Assembly can be executed through manual method or automatic system, and most of time these 2 methods should be instructed simultaneously, MANUALLY means one operator inspect Printed Circuit Board Assembly visually through visual tool in hand and make the right judgment about the defect on the Printed Circuit Board Assembly. Automatic system use computer assistant drawing analyzing method to spot the defect; people also thinks that automatic system include all the inspection methods except manually visual inspection.

X-Ray technology provides a method which can help to assess the thickness, dissipation, cavity, crack, loose weld. Ultrasonic can inspect cavity, crack and break lead. AOI can assess cosmetic features, such as bridge-connection, tin volume and shape. Laser inspection can provide 3D pictures for cosmetic features. Infrared inspection can compare an existing good quality soldering point with the inspected location, through the thermal signal difference can find the inner defect of soldering points.

There is another important point, we have already known that all the automatic inspection technology cant spot all the defects on the Printed Circuit Board Assembly. So manual visual inspection combine with automatic inspection could effectively solve this problem especially for those small quantity application. X-Ray inspection plus manual visual inspection could be the best combination of Printed Circuit Board Assembly inspection method.

Below are the main defects which has shown the highest frequency of existence on the Printed Circuit Board Assembly:
1) Component Missing;

2) Component Defect;

3) Miss registration of component;

4) Component invalidation;

5) Poor Soldering;

6) Bridge joint;

7) Insufficient soldering;

8) Tin ball;

9) Pin hole;

10) Residue;

11) Unsuitable PAD;

12) Polar upside down;

13) Lead lift;

14 ) Over length lead;

15) Cold soldering;

16) Abundant solder tin;





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