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SMT components repair process introduction

133 Published by FASTPCBA 7月 12,2019

SMT components repair process introduction

As far as the repair process of the entire SMT component is concerned, it can be divided into several steps: desoldering, component shaping, PCB pad cleaning, mounting and placing components, soldering and cleaning.

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(1) Desoldering. The process is to remove the reworked devices from the PCB which have fixed SMT component. The most basic principle is not to damage or damage the removed component itself, surrounding components and PCB welding pads. Heating control is a factor in the desoldering process and the solder must be completely melted to avoid damaging the welding pads when the components are removed.

(2) Component shaping. The components must be shaped for continuous using after desoldering . Under normal circumstances , the pins or solder balls of the removed components will have different degrees of damage, such as pin deformation of fine pitch package components and solder ball drop of BGA. The sort process of pin deformation can only be done manually. Except for the excess solder on the pins, the pin pitch should be kept consistent with the pad layout size and should not be bent or bumped. Good flatness should be kept as much as possible at the same time.

After the ball grid array package is removed, solder ball reforming is required, which is also commonly referred to as ball placement. The reforming process can be divided into four steps: one is to clean the pads on the BGA and the residual solder balls or solder on the surface of the PCB pad; the second is to uniformly apply the flux to the pad; third, prepared solder ball particles corresponding to the diameter of the component solder balls are manually transplanted to the corresponding pads, usually by means of specialized solder ball template; fourth, according to the solder ball and flux temperature requirements, the BGA that has completed the ball placement is soldered in a suitable temperature atmosphere, so that the solder ball and the pad are connected closely and reliably.

(3) PCB pad cleaning. PCB pad cleaning includes pad cleaning and alignment. Pad alignment usually refers to the flattening of the PCB pad surface from which the device has been removed. Pad cleaning is usually done by using a solder cleaning tool, a flat-head soldering iron, and assisted by a copper strip to remove the solder remaining on the pad, and then wiping off the fine substance and residual flux with anhydrous alcohol or an approved solvent ingredient. During the cleaning operation, the tin strip must be carefully held between the soldering iron nozzle and the pad to prevent the soldering iron nozzle from directly contacting the component substrate which will damage the pad.

(4) Mounting and placing components. Checking the reworked PCB with the solder paste printed; using the component placement device of the rework station, selecting the appropriate vacuum nozzle, fixing the rework PCB to be mounted and placed; using the vacuum nozzle to attach the mounted components, through the visual alignment system attached to the rework system, the PCB and the placement arm are pre-positioned to determine the component polarity or the mark pin position; after the pre-positioning is completed, the manual operation of the placement arm is smoothly moved down, so that the device pins or the solder ball directly contacts the pad to which the solder paste has been coated, and the component to be attached is placed down to complete the component mounting and placement process.

(5) Welding. The welding process of rework can be basically classified into manual soldering and reflow soldering processes, which need to be carefully considered according to the characteristics of components and PCB layout, and the characteristics of solder materials used. Manual soldering is relatively simple and is mainly used for rework soldering of small components.

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