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Written by Dr. Davide Di Maio   
Thursday, 01 October 2009 00:00

What look like open BGA joints might be tricks of the light.

Figure 1 shows a ball grid array solder joint after reflow soldering. The joint appears optically to be open, as the edge of the pad and the base of the ball are visible. In-circuit testing did not confirm any fault on the component, and x-ray showed perfect joints.


This is most likely just an optical issue; flux residues are around the base of the ball and the pad. This caused a reflection: a trick of the light rather than a defect. Optical inspection of BGA terminations requires good practical training. IPC, SMTA and SMART Group offer a BGA Inspection and Defect Guide CD-ROM on the subject, which may help train staff.

When a defect is suspected during optical inspection, always try different lighting and nondestructive inspection techniques before any destructive examination or rework.

These are typical defects shown in the National Physical Laboratory’s interactive assembly and soldering defects database. The database (, available to all Circuits Assembly readers, allows engineers to search and view countless defects and solutions, or to submit defects online. 

Dr. Davide Di Maio is with the National Physical Laboratory Industry and Innovation division (; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Last Updated on Friday, 20 November 2009 18:39


Eastern-US: China’s New Competitor?

Parity emerges among EMS Factories from Asia, Mexico and the US.

For the first time in years we see parity in the Eastern US among EMS factories from Asia, Mexico and the US. This EMS market condition will permit American OEMs (the EMS industry refers to OEMs as customers) to have more EMS pathways to choose from. Now more than ever, such EMS assignments will require deeper investigation relating to the OEMs’ evaluation of manufacturing strategies.

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For those who count on the electronics industry for big feats, it’s been a remarkable couple of years.



Advances in Concentration Monitoring and Closed-Loop Control

Contaminated bath water skews refractive index results. New technology can accurately measure aqueous cleaning agent concentration.

Circuits Disassembly: Materials Characterization and Failure Analysis

A systematic approach to nonconventional methods of encapsulant removal.





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