X-ray criteria for evaluating and judging BGA and CSP solder joint defects

- Oct 10, 2019-

Image analysis of x-ray solder joints requires software and process integration combined with IPC-A-610D acceptance criteria. In order to correctly evaluate and judge PCB soldering defects, first understand the main soldering defects of BGA and CSP, and the causes of these defects; understand the solder joint inspection standards of BGA and CSP; and use the automatic X-ray graphics analysis software correctly.

BGA's main soldering defects are voids, desoldering, bridging, internal cracks in the solder balls, cracks in the solder joints, solder joint disturbances, and cold soldering due to low soldering temperatures, incomplete solder ball melting, solder balls and PCB pads. Misalignment, ball nest, etc.

(1) Empty. The void of the Pcb solder joint is caused by the expansion of the gas and gas generated by the flux, the active agent and the metal surface oxide during the heating of the BGA during heating.

(2) Desoldering (open circuit). Solder paste is not fully melted; plastic substrate of pcb or PBGA is deformed

(3) Bridging and short circuit. There are many reasons, too many solder pastes or sticking of solder paste patterns.

(4) Cold welding and solder ball melting are not complete. It is caused by the soldering temperature being too low.

(5) Solder joint disturbance. When the solder joint cools and solidifies due to pcb vibration, or due to the expansion deformation of pcb during heating, the PCB shrinkage deformation stress caused by cooling and solidification, the surface roughness of lead-free solder joint is not affected by solder joint disturbance.

(6) The solder balls are not aligned with the pcb pads. This may be due to excessive patch offset; another reason is that the soldering temperature is too low.

(7) Ballhole defects.

1 Solder paste printed with insufficient thickness or insufficient solder paste

2 BGA coplanarity is poor

3 BGA temperature difference of four corners

4 The component or pcb is deformed during the heating process, which also occurs at the four corners of the component or where the pcb is severely deformed.

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