Inspection and countermeasures of SMT defective products
There are two main phenomena of missing components caused by the placement machine: ①The components are taken away after placement; ②The components fall off due to the movement of the X-YI table after placement. The smaller the ratio of the contact area between the component and the printed board (solder paste) to its own area, the more prone to such failures, such as class A rectangular chip components (resistors, capacitors, etc.), which have better retention force. And like B-type leaded components (diodes or triodes, etc.), due to the small contact area with the printed circuit board (solder paste), the aforementioned phenomenon is prone to occur. The reasons for the aforementioned phenomena in the placement machine can be found from the following aspects: ①There is dirt on the tip of the suction nozzle; ②Poor movement of the suction nozzle up and down; ③Poor operation of the vacuum switching valve} ④Improper mounting height adjustment; ⑤Printed board Poor clamping.
For components that have no history of failure, when the aforementioned failure phenomenon occurs, the above 5 items should be checked. Reasons other than the placement machine can also be considered from the shape of the components, the condition of the printed board, the solder paste and the bonding agent. As the main reason for the lack of components during mounting, check item by item according to this, and take corresponding countermeasures if abnormalities are found. In the event of printed board conditions, solder paste, etc., which cannot be changed for a while, avoidance methods such as reducing the placement speed or slowing down the movement speed of the worktable during placement can be adopted.
