¿Por qué es fundamental la prevención de rayones de PCB en la fabricación??

¿Por qué es fundamental la prevención de rayones de PCB en la fabricación??

/en /por

In the precision-driven production chain of the electronics manufacturing industry, scratches are one of the leading causes of PCB product scrap, rehacer, and customer complaints. Their impact goes far beyond cosmetic defects.

For products such as High-Density Interconnect (HDI) PCBS, PCB flexibles (FPCS), and boards with advanced surface finishes (P.EJ., Aceptar, immersion silver), even hairline surface damage can trigger a chain reaction of failures. Minor scratches may lead to solder mask peeling and reduced insulation performance; more severe damage can expose copper layers to oxidation, resulting in short circuits, signal transmission interference, and other functional failures — potentially causing end-product malfunction during operation.

A comprehensive PCB scratch prevention system is not a “point-based protection” at a single stage. En cambio, it requires systematic control across the entire value chain — including design (DFM), raw materials, equipo de producción, operating standards, warehousing, and logistics — to eliminate scratch risks at the source and achieve a “prevention-first, fully controlled” manufacturing objective.

This article outlines a step-by-step implementation framework that can be directly applied in practice. By combining industry case experience and technical standards, it aims to help PCB/PCBA manufacturers establish a scientific and efficient scratch prevention management system, thereby steadily improving yield rates and market competitiveness.

The Five Core Causes of PCB Scratches

Based on defect data analysis from multiple PCB factories, the vast majority of scratch defects are not accidental. En cambio, they originate from five recurring and preventable scenarios. Equipment-related and human factors account for more than 70% of cases and therefore represent the primary focus of scratch prevention control.

1. Human Factors

This is one of the most common causes and includes:

  • Direct hand contact with PCB surfaces (sweat and oil accelerate oxidation; fingernails and skin texture may cause micro-scratches)

  • Improper holding methods (P.EJ., gripping the board edge with one hand, causing bending and friction against work surfaces)

  • Dragging boards during handling, especially large-size PCBs, leading to edge friction against floors or shelves

  • Using hard metal tools such as tweezers during rework that directly contact the PCB surface

Además, insufficient systematic training and inconsistent operating discipline significantly increase the frequency of human-induced scratches.

2. Equipment and Tooling

Aging equipment and inadequate maintenance are “hidden killers” in scratch generation.

Examples include:

  • Worn conveyor rails developing burrs

  • Sharp fixture edges without chamfering or passivation

  • Hard suction nozzles (P.EJ., metal nozzles directly contacting PCB surfaces)

  • Accumulated metal debris or dust inside equipment

These issues can cause continuous scratching during board transfer and positioning.

Improper tooling design — such as insufficient contact area or excessive localized pressure — further increases the risk of localized scratches.

3. Materials and Design

Diseño de PCB flaws and raw material characteristics directly determine scratch resistance capability.

Typical issues include:

  • Solder mask thickness below 15 µm, resulting in insufficient surface hardness

  • Board-edge clearance less than 3 mm, placing traces or pads too close to edges and making them vulnerable during handling

  • Large exposed copper areas without protection (copper has relatively low hardness and is prone to abrasion)

  • Poor surface flatness of copper clad laminate (CCL) or the presence of micro-contaminants

These factors increase susceptibility to scratches during production.

4. Factores ambientales

Dust, metal particles, and fiber debris in the production environment are primary causes of “particle-induced scratches.”

These contaminants may originate from:

  • Workshop air

  • Equipment wear

  • Raw material packaging debris

Once attached to PCB surfaces or conveyor rails, they create a “grinding effect” during board movement or pressing, resulting in dense micro-scratches.

Excessive static electricity in the workshop can further attract dust onto PCB surfaces, significantly increasing scratch probability — especially during dry seasons.

5. Logistics and Handling

Scratch risks extend throughout the entire logistics chain, from production completion to customer delivery.

Common issues include:

  • Excessive horizontal stacking in warehouses, causing deformation and friction on lower boards

  • Transfer racks without separators, leading to board-to-board collision and sliding

  • Insufficient shockproof and anti-friction packaging during transportation

  • Truck vibration causing internal movement within cartons, resulting in friction between boards or packaging materials

PCB Scratch Prevention System Implementation Plan

3.1 Scratch Prevention in the DFM Design Stage (Source Control)

DFM is the first line of defense against PCB scratches. Risks should be mitigated at the design stage according to the following specifications:

Reserve a 3–5 mm board-edge keep-out zone:
Set a protective margin along board edges where routing, almohadillas, and other critical features are prohibited, ensuring a safe handling area. For large PCBs (≥500 mm × 500 mm), expand to 5 mm.

Use solder mask thickness ≥15–20 μm:
Conventional ink thickness is only 10–12 μm. Increased thickness improves wear resistance. Select ink with hardness ≥6H and qualified adhesion per IPC-SM-840.

Round board corners:
Replace right angles with rounded corners (radius ≥2 mm) to eliminate sharp edges and prevent collision scratches during handling and stacking.

Offset or protect gold finger areas:
Reserve a 0.5–1 mm offset margin or apply peelable protective film to prevent contact damage.

Avoid large exposed copper areas; use grid copper instead:
Cover copper with solder mask whenever possible. If thermal dissipation requires exposure, use grid copper (grid spacing ≥1 mm) to reduce friction area.

3.2 Raw Materials and Incoming Inspection Control

100% inspection of copper clad laminates (CCL) before storage:
Inspect for scratches, dents, and surface defects. Use 40× magnification to check micro-defects. Ensure warpage ≤0.3%.

Protective film maintained throughout storage and cutting:
Keep original protective film intact. Add PE film for temporary storage. Use soft padding on both sides during cutting.

Vertical storage on anti-static racks:
Insert boards vertically with spacing ≥5 mm. Horizontal stacking and compression are prohibited, especially for thin boards.

Incoming cleaning treatment:
Before production, remove dust using soft brushes and industrial vacuum cleaners. High-pressure air guns are prohibited.

3.3 Scratch Control at Key Production Processes

Corte / V-Scoring / Enrutamiento

Use top-cut blades:
Reduce bottom surface friction. Maintain blade sharpness and replace every 20,000 paneles.

Install foam backing board:
Place ≥5 mm high-density foam board on worktable. Clean and replace regularly.

Frequent debris cleaning:
Pause every 100 panels to remove debris from blades and work surfaces.

Drilling Process

Apply aluminum entry sheet:
Cover top surface with 0.1–0.2 mm aluminum foil to prevent drill scratches.

Use backup board underneath:
Use phenolic resin backup boards and replace every 500 panels to reduce burrs.

Clean spindle and worktable:
Before each batch, clean spindle and guide rails; inspect locating pins for burrs.

Enchapado / Desarrollo & Aguafuerte (DES)

Use coated or rubber-lined fixtures:
Contact surfaces should use polyurethane or rubber; control clamping force.

Control conveyor speed:
Maintain 1–2 m/min. For thin boards, install silicone guide wheels with 0.1–0.2 mm clearance.

Regular roller maintenance:
Polish weekly with fine sandpaper. Replace when wear exceeds 0.1 mm.

Máscara de soldadura y serigrafía

Use mild micro-etching process:
Control micro-etch depth at 0.5–1.0 μm to avoid adhesion reduction from over-etching.

Use soft squeegee:
Polyurethane squeegee (Shore hardness 60–70), pressure 0.1–0.3 MPa.

Ensure full ink curing:
Strictly follow curing parameters. Hardness ≥6H; cross-hatch adhesion ≥4B.

Insert separators during curing:
When placed flat, use 1–2 mm high-temperature silicone spacers between boards.

Acabado de superficies (Aceptar, Sangrar, Estaño de inmersión, etc.)

Use soft conveyor rails:
EVA (Shore 30–40) or silicone (Shore 40–50) rails with 0.1–0.2 mm clearance.

Avoid direct metal contact with finished surfaces:
Use plastic or ceramic fixtures and anti-static rubber gloves.

Precisely control temperature and tension:
HASL temperature 245–255°C; ENIG tension 5–10 N to prevent abrasion.

3.4 Inspection and AOI Stage

Install cushioning under test probes:
Use 5–8 mm silicone or polyurethane pads; replace every 1,000 paneles.

Control probe pressure:
For sensitive boards (P.EJ., Aceptar), single probe pressure ≤50 g.

Use non-abrasive test fixtures:
Contact areas made of nylon or polyurethane with rounded edges; conduct scratch testing before use.

Enable side-light AOI inspection:
Use angled lighting to detect micro-scratches (width ≥0.01 mm) and mark for analysis.

3.5 Handling and Operational Standards (Obligatorio)

Mandatory anti-static finger cots/gloves:
Must be worn at all times and replaced daily. Bare-hand contact is prohibited.

Vertical handling of boards:
Hold board edges and lift vertically. No sliding or dragging. Large boards require two operators.

Use anti-static dust-free racks with partitions:
Single-board slots with soft separators, spacing ≥10 mm, stacking ≤3 layers.

Limit stacking height:
Strict height limits by board thickness. Insert PE film or EVA foam every 10 tablas.

Use ceramic or plastic-coated tweezers for rework:
Metal tweezers are strictly prohibited.

Establish deep-cleaning schedule for worktables:
Vacuum every 2 horas; wipe daily with isopropyl alcohol.

3.6 Cleaning and Environmental Control

Use industrial vacuum cleaners with soft brushes:
High-pressure air guns are prohibited to avoid secondary contamination.

Maintain cleanroom standards at final inspection:
Class 1,000–10,000 cleanroom with air shower and HEPA filtration.

Static and humidity control:
Relative humidity 45%–65%; conexión a tierra adecuada; wrist straps required; body static ≤100 V.

Daily cleaning of rails, fixtures, and worktables:
Before and after production, wipe contact areas with lint-free cloth and isopropyl alcohol.

3.7 Embalaje, Warehousing, and Transportation

Individual packaging for each board:
Cover with PE film, then place in anti-static bag. Use pearl cotton for high-end boards.

Anti-static tray + shockproof carton packaging:
Line tray grooves with EVA pads; carton lined with pearl cotton; ≤3 trays per carton.

Prefer vertical storage; limit stacking weight:
Store vertically; carton stacking ≤2 layers; environment 18–25°C, 45%–65% RH.

Use anti-shock and anti-friction materials for long-distance transport:
Add wooden outer box with foam lining; use enclosed trucks with anti-static floor mats.

Clear outer labeling:
Mark “Fragile,” “No Stacking,” “Anti-Static,” and upward arrows clearly on outer packaging.

PCB Scratch Prevention Critical

PCB Scratch Prevention Critical

Equipment and Tooling Maintenance System

Más que 70% of scratch defects are related to equipment aging, wear, or untimely cleaning. Establishing a standardized equipment and tooling maintenance system is the core measure to ensure the long-term effectiveness of scratch prevention controls.

Daily Inspection: Rails, Rollers, Carriers, Fixtures, and Nozzles

Before daily production, maintenance personnel must conduct a comprehensive inspection of all equipment parts that come into contact with PCBs.

Key inspection points include:

  • Whether guide rails are smooth and free of burrs or wear marks

  • Whether rollers rotate smoothly and have no dents or surface contamination

  • Whether coatings on carriers and fixtures are peeling and whether rubber components are aging

  • Whether suction nozzles have hardened or contain surface residues

Any issues identified (such as rail burrs or coating delamination) must be corrected immediately through polishing or replacement. Production may only begin after confirming compliance with scratch prevention requirements.

During production, operators must continuously monitor equipment status. If abnormalities occur (such as board transfer jams or unusual noise), production must be stopped immediately and maintenance personnel notified.

Weekly Maintenance: Polishing and Replacement of Worn Components

A comprehensive maintenance procedure shall be conducted weekly, focusing on high-wear components.

  • Lightly polish guide rails and rollers with ≥800-grit sandpaper to remove minor wear marks and residues, then clean with isopropyl alcohol.

  • Inspect coatings on fixtures and carriers. If coating wear exceeds 30% of the surface area, replace the coating or the entire component.

  • Clean internal residues from suction nozzles. If nozzle hardness exceeds Shore 60, replace with soft nozzles.

  • Inspect lubrication systems and apply dust-free, non-corrosive specialty lubricants to ensure smooth operation and minimize friction-induced wear.

Monthly Calibration: Presión, Speed, and Positioning Accuracy

Critical equipment parameters must be calibrated monthly to ensure compliance with scratch prevention standards.

Calibration items include:

  • Conveyor transmission speed (tolerance ≤ ±5%)

  • Fixture clamping pressure (tolerance ≤ ±10%)

  • Drilling machine positioning accuracy (tolerance ≤ ±0.02 mm)

  • Test probe pressure (tolerance ≤ ±5 g)

Calibration must be performed by qualified technicians using professional instruments (P.EJ., laser measuring devices, pressure sensors). Results shall be recorded in equipment maintenance logs.

Equipment that fails calibration must be shut down and adjusted until parameters meet standards before resuming production.

Maintenance Records and Traceability

An independent maintenance log shall be established for each production machine and tooling set. Records must include:

  • Daily inspection results

  • Weekly maintenance activities

  • Monthly calibration data

  • Component replacement history

Each record must include maintenance date, responsible personnel, issue description, corrective action, and effectiveness verification.

By analyzing maintenance logs, wear patterns can be identified and preventive maintenance plans implemented. Por ejemplo, if a specific rail model shows severe wear every three months, proactive replacement can be scheduled to prevent scratch defect outbreaks.

Maintenance records must be archived and retained for no less than one year to support quality traceability and equipment optimization.

Quality Management and Continuous Improvement

Establishing a comprehensive quality management system to monitor and continuously improve scratch defect control is an essential part of the PCB full-process scratch prevention system.

Scratch Classification Standard (Visual + Microscopic Inspection)

To standardize defect evaluation, scratches shall be classified into four levels based on visual and microscopic inspection:

Nivel 1 (Minor Scratch):
Width ≤ 0.01 mm; length ≤ 0.5 mm; no exposed copper; no solder mask peeling; no impact on appearance or function. Acceptable for shipment.

Nivel 2 (Moderate Scratch):
Width 0.01–0.03 mm; length 0.5–1.0 mm; no exposed copper; no solder mask peeling; cosmetically acceptable. Shipment subject to customer approval.

Nivel 3 (Severe Scratch):
Width 0.03–0.05 mm; length 1.0–2.0 mm; or localized copper exposure or solder mask peeling present. Affects appearance. Rework required.

Nivel 4 (Critical Scratch):
Width ≥ 0.05 mm; length ≥ 2.0 mm; or exposed copper area ≥ 0.1 mm². Functional impact. Scrap directly.

Inspection procedure:
First conduct visual inspection at a distance of 30 cm from the PCB surface under illumination ≥500 lux. If a suspected scratch is found, measure with a 40× microscope and classify according to the standard.

100% Inspection for High-End Boards

PCB de alta gama (P.EJ., HDI, FPC, and medical-grade PCBs) requerir 100% inspection due to strict surface treatment and reliability requirements.

Inspection scope includes:

  • Inspección visual (naked eye + microscope)

  • Pruebas de rendimiento eléctrico

  • Adhesion testing

Any scratch defects identified must be marked and isolated immediately. Root cause analysis and corrective actions must be implemented to prevent recurrence.

For standard PCBs, sampling inspection shall follow AQL standards (Appearance Defects AQL = 1.5). Sampling ratios shall increase with batch size.

Core Value of the Full-Process Scratch Prevention System

A scientific and comprehensive PCB scratch prevention system not only reduces defect rates but also delivers multidimensional strategic value.

Reduced Scrap and Rework Costs

Scratch defects are a major cause of scrap and rework. Through full-process control, defect rates can be reduced from the industry average of 3–5% to below 1%, or even achieve “zero scratches.”

For a manufacturer producing 1 million PCBs annually at an average cost of RMB 100 por tablero, reducing the scratch rate from 4% a 1% saves approximately RMB 3 million per year (1,000,000 × 3% × 100), directly improving profitability.

Improved Yield and Process Stability

Full-process control ensures standardization across design, fabricación, and logistics stages, minimizing production interruptions and batch rework caused by scratches.

Higher yield improves raw material utilization and production efficiency, enabling greater output within the same production cycle and enhancing delivery capability.

Reduced Customer Complaints and Return Risk

Scratch defects are a major source of customer complaints, especially in industries such as automotive electronics and medical equipment, where reliability standards are stringent.

Effective scratch prevention can reduce complaint rates by over 80%, improve customer satisfaction and loyalty, and secure long-term partnerships.

Lower Material Waste and Labor Costs

Scratch-related scrap and rework increase material waste and labor costs. A prevention-focused system reduces unnecessary losses and minimizes rework and re-inspection workloads, improving overall operational efficiency.

Support for ISO and IPC Certification

Quality certifications such as ISO 9001 and IPC-A-600 (PCB acceptability standards) impose strict requirements on defect rates and process control.

A full-process scratch prevention system helps meet certification requirements and supports entry into high-end markets such as automotive and aerospace, where stringent defect control capability is mandatory.

Enhanced PCB/PCBA OEM/ODM Competitiveness

In an increasingly competitive PCB market, product quality is a core competitive advantage.

Manufacturers capable of delivering “zero-scratch,” high-reliability PCBs gain stronger recognition in high-end OEM/ODM markets. A robust scratch prevention system provides differentiation and increases opportunities for premium orders and market share growth.

Conclusión

PCB scratch prevention is not a single operational measure but a comprehensive closed-loop management system spanning design, producción, logística, y control de calidad.

From risk elimination at the DFM stage, to process-level protection during manufacturing, to multi-layer packaging in warehousing and transportation, each stage must strictly implement standardized scratch prevention practices. Equipment maintenance, personnel training, and continuous quality improvement mechanisms ensure long-term effectiveness.

For PCB/PCBA enterprises, establishing a full-process scratch prevention system is not only essential for reducing defect rates and improving yield, but also a strategic necessity for transitioning toward high-end manufacturing and strengthening market competitiveness.

As PCB technology advances toward higher density, thinner profiles, and more premium applications, scratch control challenges will intensify. Companies must continuously monitor industry developments, adopt advanced materials, equipo, and inspection technologies, and refine their scratch prevention systems to meet evolving market demands.