What Are The Guidelines for Electrical Refurbishment?

1. Rework rework basis: rework rework does not have the design documents and regulations, not approved in accordance with the relevant provisions, no dedicated rework rework process protocols.

2. The number of rework allowed for each solder joint: rework is allowed for defective solder joints, and the number of rework for each solder joint shall not exceed three times, otherwise the solder part is damaged.

3. The use of removed components: removed components in principle should not be used again, if you need to use, must be in accordance with the original electrical properties of components and process performance screening test, meet the requirements before allowing the installation.

4. The number of desoldering on each pad: each printed pad should only be desoldering operation (that is, only allow one replacement of components), a qualified solder joint intermetallic compound (IMC) thickness of 1.5 to 3.5µm, the thickness will grow after remelting, even up to 50µm, the solder joint becomes brittle, the welding strength decreases, there are serious reliability risks under vibration conditions; and remelting IMC requires higher temperature, otherwise it is not possible to remove IMC. The copper layer at the exit of the through-hole is the thinnest, and the pad is prone to fracture from here after remelting; with the thermal expansion of the Z-axis, the copper layer deforms, and the pad detaches due to the obstruction of the lead-tin solder joint. Lead-free case will pull up the entire pad: PCB due to glass fiber and epoxy resin with water vapor, after heat delamination: multiple welding, the pad is easy to buckle, and the substrate separation.

5. Surface mount and mixed installation PCBA assembly after welding bowing and distortion requirements: surface mount and mixed installation PCBA assembly after welding bowing and distortion of less than 0.75% of the requirements

6. Total number of PCB assembly repair: the total number of repair of a PCB assembly is limited to six, too much rework and modification affect reliability.