Cause Analysis of Defects in BGA Rework Table Welding

March 23, 2023

During BGA soldering using a BGA rework station, BGA soldering may be poor due to manual operations or mechanical equipment.Only relevant adjustments are made based on known conditions, so we analyze the causes of defects caused by welding.

1. Poor BGA bridging can easily occur when the BGA rework station welds BGA components, the solder ball is connected to the solder ball, resulting in a short circuit, that is, solder joint bridging, which can be detected by X-ray.The main causes of tin connection are: poor printing of solder paste, not allowed placement, uneven or excessive flux, excessive soldering pressure when automatically soldering BGA rework station, BGA corner warping or other causes of arching.2. BGA air soldering, at this time, the appropriate solder balls should be selected. In the standard process, solder paste is usually applied to the PCB pad before reflow soldering.Therefore, using solder balls of the same size when using a BGA rework station will result in insufficient tin.At this time, large solder balls should be used to ensure the mechanical strength of the solder, the height of the BGA pad and the PCB pad.For example, the 0.8mm pitch BGA pad standard should use 0.4mm solder balls, but the industrial production design uses a solder paste process, so to get enough tin, 0.45mm solder balls can be used.3. BGA cold welding can lead to electrical performance failure or malfunction, so that the solder balls can not be completely melted. When welding BGA, the BGA rework table does not reach a high enough temperature, which leads to some solder balls can not be completely melted, and the solder paste and BGA solder balls are not completely wetted.The solder balls are still in a state of not being able to reach a complete melting state, that is, the mixture that is still in a liquid solidification state is cooled, and the surface of the solder balls of the stroke is rough and uneven, and there is no rule.With 2D/X-ray detection, the image has a blurred edge contour with a burr-like irregular projection along the perimeter.Even if the solder joint is cold-soldered, the mechanical strength of all solder joints is reduced, resulting in electrical failure or malfunction.4, BGA solder joints, most of which are caused by external reasons in the production of BGA due to poor storage, storage and delivery, resulting in surface metal surface oxidation, vulcanization and pollution (grease, sweat, etc.) Or surface solderability coating quality problems, resulting in solderability loss.After soldering, there is no strong alloy bond between the pad and pad, resulting in a continuous and reliable electrical signal, which is mainly due to external reasons.In general, the BGA assembly that appears during debugging uses an external force to press the signal, and when there is no signal after the external force disappears, we believe that this is a typical "soldering" phenomenon.5. Component deformation, which can be seen directly from the appearance. In BGA soldering, the thermal expansion coefficients of various materials inside the component are different, which causes the package to warp after the internal materials are heated during heating.Or the part is moist inside and not preheated prior to heating, which causes the internal moisture to evaporate and expand as the weld heats up, causing the popcorn phenomenon of the part.Therefore, it is possible to preheat the weld first and reduce the peak temperature as much as possible while ensuring the quality of the weld.The unit is stored and installed to enhance moisture management.

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