2022-12-16
What are the requirements for pcba rework and repair?
Today, I will tell you what are the requirements for pcba rework and repair? The conditions and specifications for pcba rework and repair. There will be rework and rework in PCBA processing. Only reasonable operation based on scientific guidelines can guarantee the quality of PCBA boards. Next, I will introduce the rework and rework guidelines for PCBA processing.
pcba rework and rework conditions and specifications
1. Basis for PCBA processing and rework
PCBA processing rework and rework must be carried out in accordance with PCB design documents and rework regulations, and there must be a unified rework and rework process procedure.
2. Allowable rework times per solder joint
Rework is allowed for defective solder joints, and the number of rework for each solder joint shall not exceed three times, otherwise it will cause damage to the solder joints.
3. Use of removed components
In principle, the removed components should not be used again. If they need to be used, they must be screened and tested according to the original electrical performance and process performance of the components. Only when they meet the requirements can they be installed.
4. Desoldering times on each pad
Each printed pad should only be desoldered once (that is, components are only allowed to be replaced once). The thickness of the intermetallic compound (IMC) of a qualified solder joint is 1.5 to 3.5 µm, and the thickness will increase after remelting, or even When it reaches 50µm, the solder joints become brittle, the welding strength decreases, and there are serious reliability risks under vibration conditions;
And remelting IMC requires a higher temperature, otherwise IMC cannot be removed. The copper plating layer is the thinnest at the exit of the through hole, and the pad is easy to break from here after remelting; with the thermal expansion of the Z-axis, the copper layer is deformed, and the pad is detached due to the obstruction of the lead-tin solder joint.
In the case of lead-free, the entire pad will be pulled up. The PCB will be delaminated after being heated due to the water vapor of the glass fiber and epoxy resin. After repeated soldering, the pad is easy to warp and separate from the substrate.
5. Bow and twist requirements for surface mount and hybrid mount PCBA assemblies after soldering
Surface mount and hybrid mount PCBA assemblies require that bow and twist be less than 0.75% after soldering.
6. Total number of PCB assembly repairs
The total number of repairs for a PCB assembly is limited to six, and excessive rework and modification affect PCBA reliability.
pcba rework and rework conditions and specifications
1. Basis for PCBA processing and rework
PCBA processing rework and rework must be carried out in accordance with PCB design documents and rework regulations, and there must be a unified rework and rework process procedure.
2. Allowable rework times per solder joint
Rework is allowed for defective solder joints, and the number of rework for each solder joint shall not exceed three times, otherwise it will cause damage to the solder joints.
3. Use of removed components
In principle, the removed components should not be used again. If they need to be used, they must be screened and tested according to the original electrical performance and process performance of the components. Only when they meet the requirements can they be installed.
4. Desoldering times on each pad
Each printed pad should only be desoldered once (that is, components are only allowed to be replaced once). The thickness of the intermetallic compound (IMC) of a qualified solder joint is 1.5 to 3.5 µm, and the thickness will increase after remelting, or even When it reaches 50µm, the solder joints become brittle, the welding strength decreases, and there are serious reliability risks under vibration conditions;
And remelting IMC requires a higher temperature, otherwise IMC cannot be removed. The copper plating layer is the thinnest at the exit of the through hole, and the pad is easy to break from here after remelting; with the thermal expansion of the Z-axis, the copper layer is deformed, and the pad is detached due to the obstruction of the lead-tin solder joint.
In the case of lead-free, the entire pad will be pulled up. The PCB will be delaminated after being heated due to the water vapor of the glass fiber and epoxy resin. After repeated soldering, the pad is easy to warp and separate from the substrate.
5. Bow and twist requirements for surface mount and hybrid mount PCBA assemblies after soldering
Surface mount and hybrid mount PCBA assemblies require that bow and twist be less than 0.75% after soldering.
6. Total number of PCB assembly repairs
The total number of repairs for a PCB assembly is limited to six, and excessive rework and modification affect PCBA reliability.
