PCBA repair process

The PCBA (Printed Circuit Board Assembly) rework process is a procedure for locating faults in assemblies with poor soldering or functional failures, removing defective components, and re-soldering qualified components. Statistics show that approximately 5%-15% of PCBA require rework during electronic product manufacturing.

Rework addresses issues such as soldering defects and component failures during production, with the repaired product needing to meet original production standards; repair deals with faults caused by aging, improper use, etc., in already-used products. An excellent industry standard is to control the rework defect rate within 3%.

The typical process is: fault detection → defect location → component removal → pad cleaning → new component soldering → inspection and verification. Among them, component removal and soldering account for 60%-70% of the total process time.

Even in advanced SMT production lines, there is still a soldering defect rate of 0.1%-1% (such as cold soldering and bridging). Rework can improve product qualification rates, reduce production costs, and avoid scrapping the entire board.

It can improve product first-pass yield, reduce production costs, ensure product quality and reliability, and lower after-sales maintenance costs. Studies show that good rework processes can increase product reliability by 20%-30%.

Mainly includes hot air rework stations, infrared rework stations, BGA rework stations, desoldering pumps, microscopes, etc. Among them, BGA rework stations have a temperature control accuracy of ±1℃, suitable for high-precision BGA component rework.

It generates hot air through a heating tube, and blows the hot air onto the components to be reworked through a nozzle, melting the solder to achieve removal or soldering. The hot air temperature is generally adjustable from 200-450℃, with an airspeed of 5-50L/min.

BGA rework stations have independent temperature control functions for multiple temperature zones, enabling complex temperature curve control, suitable for packaged devices such as BGA and CSP; common hot air rework stations are mostly used for conventional packages like QFP and SOP. The price of a BGA rework station is about 3-5 times that of a common hot air rework station.

They are divided into manual desoldering pumps, electric desoldering pumps, and vacuum desoldering guns. Manual desoldering pumps are suitable for removing a small number of solder joints, electric desoldering pumps are more efficient, and vacuum desoldering guns are suitable for multi-pin components. Electric desoldering pumps remove solder 3-5 times faster than manual ones.

For tiny packaged devices such as 0201 and 01005, a microscope with a magnification of 50-100 times is required; for conventional packaged devices, 10-30 times magnification is sufficient. High-magnification microscopes are about 2-3 times more expensive than low-magnification ones.

Set according to component packaging and solder type. For Sn63Pb37 solder, the removal temperature is generally 350-380℃, and the soldering temperature is 320-350℃; for lead-free solder (such as SAC305), the removal temperature is 380-420℃, and the soldering temperature is 350-380℃. Excessively high temperature easily damages components, while too low temperature prevents the solder from melting.

It usually includes a preheating zone (heating rate 1-3℃/s, temperature 120-150℃), a soaking zone (150-180℃, 60-120s), a reflow zone (peak temperature 217-235℃, maintained for 30-60s), and a cooling zone (cooling rate 2-4℃/s). Improper setting of the temperature curve can cause problems such as BGA cold soldering and solder ball cracking.

Excessively high airspeed can blow away small-sized components or cause solder splashing; too low airspeed results in insufficient heat transfer. Generally, the airspeed for 0402 and above packages is set at 10-20L/min, and for 0201 and below, it is 5-10L/min.

It is recommended that the soldering time for a single solder joint does not exceed 3 seconds, and continuous soldering does not exceed 10 seconds. Excessively long soldering time increases the risk of PCB copper foil peeling off by 30% and the probability of component damage by 25%.

Adjust according to PCBA size and component density, generally with a power density of 1-3W/cm². Excessively high power can cause local overheating and deformation of the PCB, while too low power results in low heating efficiency.

Use a hot air rework station, aim the nozzle at the pins, heat at 350-380℃ with an airspeed of 15-20L/min, and remove the component with tweezers after the solder melts. After removal, clean the pads with desoldering wick.

First, set an appropriate temperature curve. After the solder balls are completely melted, carefully remove the BGA with a vacuum suction pen; clean the residual solder on the pads and reball using solder paste. The success rate of BGA removal is 85% due to the matching of the temperature curve.

Record the polarity direction of the component to avoid reverse installation; pay attention to uniform heating during removal to prevent component explosion due to local overheating. Incorrect polarity installation increases product failure rate by 40%.

In such cases, X-ray inspection is required to determine the solder joint positions, and local heating methods (such as laser heating) are used for removal. It is quite difficult, with a success rate of only 60%-70%.

Control the heating temperature and time, and avoid repeated heating of the same position; use appropriate tools, such as using a pry bar to assist in removing large-sized components to reduce pulling on the PCB. Correct operation can reduce PCB damage rate by 50%.

Clean residual solder on pads using desoldering wick with a soldering iron: soak the wick in flux, place it on the pad, and heat with the iron to absorb the solder. Match the wick width to the pad to avoid excessive or insufficient cleaning.

Gently sand the oxidized layer with fine sandpaper, apply flux, and heat to restore solderability. Untreated oxidized pads can cause an 80% soldering defect rate.

For partial detachment, use jumper wires; for complete detachment, remake the pad (copper plating, solder mask coating) and test electrical performance after repair.

Use a chisel-shaped soldering iron tip to level excess solder, and sand if necessary. Flatness error must be within ±0.05mm to avoid soldering issues.

Yes. Use anhydrous ethanol or specialized cleaning agents to remove residual flux and impurities, avoiding a 20% increase in soldering defects and PCB corrosion.

Check component specifications, tin the pads, and prepare appropriate tools and flux. Inadequate preparation can cause a 30% rework rate.

Use a microscope and hot air rework station or pointed soldering iron. Fix one pin first, then solder the rest to ensure accurate positioning.

Use X-ray to inspect solder ball connections (void rate ≤5%) and a multimeter for electrical continuity. X-ray detects over 90% of defects.

Fix components with adhesive or flux before soldering, and heat evenly to avoid thermal stress. Shifting accounts for 15%-20% of soldering defects.

Copper leads are highly solderable; iron leads require pre-tinning; alloy leads need matching flux. Untreated iron leads have a 70% soldering defect rate.

Includes visual inspection, electrical performance tests (continuity, insulation resistance), and functional testing. Visual inspection finds 70%-80% of obvious defects.

Check for full, smooth solder joints without cold soldering, bridging, or icicles; ensure leads are fully soldered and undamaged. Compliance with IPC-A-610 standards is required.

Detects internal solder joint quality of BGA/CSP components, identifying cold soldering, cracked solder balls, and voids, with over 95% defect detection rate for internal issues.

Tests electrical performance via bed-of-nails fixtures, detecting shorts, opens, and component parameter issues, covering 80%-90% of electrical connections.

Integrate the PCBA into a system to simulate real working conditions and test functionality, identifying 90% of welding-induced functional failures.

Causes: unclean pads, insufficient temperature, ineffective flux. Solutions: reclean pads, adjust temperature/time, and replace flux with high-quality alternatives.

Remove excess solder with desoldering wick/iron, adjust soldering temperature and airspeed to prevent splashing. Proper handling achieves a 95% repair rate.

Possible causes: component damage, overheating during soldering, reverse polarity. Statistics show component damage accounts for 40%, overheating for 30%.

Correct minor deformation by heating; replace PCBs for severe deformation. Controlling temperature/time reduces deformation rate by 60%.

Use ESD-safe workbenches, wrist straps, and tweezers; maintain 40%-60% RH humidity to reduce ESD damage by 90%.

Operators must wear protective glasses/gloves to prevent burns; ground equipment to avoid electric shock; mark high-temperature equipment with warning signs.

Waste components, solder, and flux are hazardous waste, requiring disposal by qualified units; cleaning wastewater must meet GB 8978 discharge standards.

Most fluxes are flammable and should be stored in cool, ventilated areas away from fire sources; avoid skin/eye contact and flush with water immediately if exposed.

Regularly clean solder residue and flux from equipment; install overheat protection to automatically power off when temperature limits are exceeded.

Must comply with RoHS directives, restrict hazardous substances like lead/mercury/cadmium, minimize flux volatilization, and use eco-friendly cleaning agents.

Optimize processes, adopt automated equipment, and train operators. Automated equipment can increase efficiency by 30%-50%.

Reduce secondary rework due to improper operation, select tools/materials rationally, and optimize processes to lower initial defect rates. Secondary rework accounts for 25%-35% of total costs.

Optimize process parameters, select appropriate flux/solder, and strengthen first-article inspection and in-process sampling. Process improvements can reduce defect rates by 40%-60%.

Improves quality stability, reduces human error, facilitates new employee training, and enhances efficiency. Standardization can narrow defect rate fluctuations by 50%.

Conduct aging tests (24-100 hours) and environmental tests (high temperature/humidity/vibration) on reworked products to evaluate long-term reliability.

It is necessary to consider the rework requirements of both SMT and THT components. When removing THT components, attention should be paid to the impact on SMT devices. The rework difficulty is 30%-50% higher than that of pure SMT boards.

The material is soft and easy to deform, so special fixtures are required for fixing; the heating temperature should be 10-20℃ lower than that of rigid PCB to avoid damaging the substrate.

The internal circuit is complex, and the heat transfer is uneven during heating, which is prone to cause short circuit or open circuit of the inner layer; the pad repair is difficult, and the rework success rate is only 50%-60%.

Remove the shielding cover first and protect the internal components. Reinstall it after rework to ensure the shielding effect. Improper operation will affect the electromagnetic compatibility.

It has good thermal conductivity and high brittleness. It needs rapid heating to avoid cracking caused by local stress concentration, and the heating rate is preferably controlled at 5-10℃/s.

They need to master skills such as component identification, welding technology, equipment operation, and fault analysis, and be familiar with standards such as IPC-A-61 The defect rate of professionally trained personnel is 40% lower than that of novices.

It includes theoretical training (process knowledge, standard specifications) and practical training (equipment operation, welding practice), with assessment after training, and the cycle is generally 1-2 weeks.

It includes rework process instructions, equipment operation manuals, quality inspection standards, rework records, etc., which can improve traceability and problem analysis efficiency.

Set key control points (such as component removal, pad cleaning, welding, etc.), and carry out first-piece inspection, patrol inspection and finished product inspection, which can reduce the defect rate by 30%-40%.

Collect rework data to analyze problems, carry out process tests to optimize parameters, and introduce new technologies and equipment, which can increase efficiency by 10%-15% annually.

Select according to the original PCBA solder type, give priority to products with similar composition, and consider performance such as melting point, wettability, and reliability.

They are divided into no-clean flux, water-soluble flux and rosin-based flux. No-clean flux is suitable for occasions with low cleanliness requirements, and water-soluble flux is convenient for cleaning but residual should be noted.

It is used to fix tiny components or prevent displacement during welding, and needs to have good bonding strength (≥5N/mm²) and temperature resistance.

Select according to the flux type (such as isopropyl alcohol for rosin-based), and consider environmental protection, corrosion and volatility.

It is necessary to check the model, specification, appearance, electrical performance, etc. to ensure consistency with the original components. Poor incoming materials will increase the rework failure rate by 20%.

Clean the impurities inside the air nozzle to prevent blockage, check the status of the heating tube and calibrate the temperature regularly, and lubricate the mechanical components. Air nozzle blockage will increase the welding defect rate by about 15%.

The temperature is calibrated once a month (error ≤±1℃), and the Z-axis height is calibrated once a quarter (accuracy ≤±0.05mm). Uncalibrated may increase the welding void rate by 20%.

Insufficient suction: replace the seal ring for manual desoldering pump, check the vacuum pump or clean the blockage for electric desoldering pump; unable to desolder: check whether the nozzle is damaged or blocked, replace and clean the residual solder.

Generally, it is replaced every 1-2 years according to the usage frequency. After aging, the temperature uniformity decreases, and the welding defect rate increases by about 12%.

Regularly clean the lens with special lens paper, avoid collision to prevent the displacement of optical components, and calibrate the focal length every year to ensure clear imaging.

First use chemical solvents (such as acetone) to dissolve the encapsulation material, rework according to the conventional process after removal, and re-encapsulate after completion, paying attention to the fluidity and curing conditions of the material.

Priority is given to removing large-size and high-heat-generating components to avoid affecting the repaired parts; follow the principle from easy to difficult to reduce risks.

Special equipment (such as flip chip rework station) is required, and laser heating or ultrasonic welding technology is used. Parameters are determined through pre-testing, and the success rate is usually 60%-70%.

Use a multimeter for continuity testing to locate the short circuit point, and check and solve problems such as solder residue bridging, component pin misalignment, and PCB circuit damage.

Check whether the grounding is good and the shielding cover is installed in place, check whether the signal line is damaged during welding, use a spectrum analyzer to detect the interference source, and take measures such as shielding and filtering.

Analyze rework data through machine learning to predict defects, use visual recognition to automatically locate defective components, and intelligently adjust equipment parameters to improve efficiency and quality.

It will develop towards high-precision and multi-function integration (such as integrating X-ray inspection, automatic ball planting, welding, etc.), and realize interconnection with MES system to improve intelligent management.

Promote environment-friendly flux and cleaning agents, develop low-energy consumption equipment, and explore non-destructive rework technology to reduce pollution and resource waste.

It can quickly manufacture fixtures for rework to reduce costs, and is used to repair local damage of PCB (such as printing conductive lines) to simplify complex processes.

Realize digital control and remote monitoring of rework equipment, optimize processes through big data analysis, and establish product rework traceability systems to improve quality control.