Qué pruebas hacer con PCB？

What Tests Are Required for PCB Manufacturing?

In the manufacturing process of electronic products, the quality of PCB (Placa de circuito impreso) directly determines the performance and reliability of the final product. There may be hundreds of components and thousands of solder joints on a circuit board, and any minor defects may cause the entire system to fail. How to ensure product quality, reducing production costs, and improving market competitiveness is very important.

The Benefits of PCB Testing

PCB testing is a critical part of ensuring board quality and reliability

1. Early Detection of Design Defects: Comprehensive testing identifies functional and manufacturability issues in PCBs, allowing designers to make timely adjustments and optimizations.
2. Significant Cost Reduction: Discovering problems during the prototyping phase saves over 90% of costs compared to identifying issues after mass production, avoiding catastrophic batch failures.
3. Shorter Time-to-Market: Quickly pinpointing root causes accelerates design iterations, enabling faster launch of mature products than competitors.
4. Enhanced Brand Reputation: Reducing return rates to below 1% improves customer satisfaction and builds market credibility.
5. Ensured Safety: Prevents accidents like fires or electric shocks caused by PCB failures, protecting users’ lives and property.

What PCBs are mainly tested for？

The purpose of PCB testing and inspection is to check the performance of PCBs against standard printed circuit boards. It ensures that all PCB manufacturing processes are functioning properly and without any defects as per the project specifications. A PCB consists of different elements, components, each of which affects the overall performance of the electronic circuit. These elements are analyzed in detail to ensure PCB quality and improve product reliability.

1. Pore wall quality

Hole walls are typically analyzed in environments with cycling and rapid temperature changes to understand their response to thermal effects. This ensures that the vias will not crack or delaminate when the PCB is put into service, which could cause the PCB to fail.

2. Copper Plating

Copper foils on printed circuit boards are affixed to the board to provide electrical conductivity. The quality of the copper is tested, and the tensile strength and elongation are analyzed in detail to ensure that the circuit is smooth.

3. Cleanliness

The cleanliness of a printed circuit board is a measure of the board’s ability to withstand environmental factors such as weathering, corrosion, and humidity, which may allow the PCB to last longer.

4. Solderability

Solderability tests are performed on materials to ensure that components can be securely attached to the board and to prevent soldering defects in the final product.

5. Electrical Testing

Conductivity is critical to any PCB, as is the ability to measure the PCB’s minimum leakage current.

6. Environmental Testing

This is a test of the PCB’s performance and quality changes when operating in a humid environment. Weight comparisons are usually made before and after placing the PCB in a humid environment, and if the weight changes significantly, it is considered scrap.

8 Key Testing Methods in PCB Manufacturing

1. Visual Inspection

As the most basic detection method, visual inspection requires experienced technicians to examine obvious surface defects using magnifiers or microscopes (typically 5-10x magnification).

Key Inspection Points:

• Pad oxidation and contamination
• Complete circuit etching, checking for open or short circuits
• Even solder mask coverage, checking for bubbles or peeling
• Correct component placement and polarity
• Solder joint glossiness and shape compliance with standards

Ventajas: Extremely low cost, no specialized equipment needed, suitable for businesses of all sizes.

Limitaciones: Manual inspection is slow (~2-5 minutes/board), detects only ~70% of surface defects, is ineffective for hidden solder joints like BGAs, and is highly dependent on operator experience and condition.

2. Inspección óptica automatizada (AOI)

AOI systems use high-resolution cameras (up to 50μm precision) to capture PCB images from multiple angles. Image processing algorithms compare these with standard templates to detect most surface assembly defects.

Typical Detection Capabilities:

• Missing, wrong, or reversed components
• Excessive or insufficient solder
• Lifted leads, tombstoning
• Abnormal solder ball diameter or pitch
• Incorrect markings or silkscreen

Parámetros técnicos:

• Inspection speed: 0.5-2 seconds/board
• Minimum detectable size: 0201 components (0.6×0.3mm)
• False alarm rate: <3%

Implementation Recommendation: AOI should be deployed at two critical stations—post-reflow and post-wave soldering—and integrated with SPC systems for real-time process adjustment.

3. In-Circuit Test (ICT)

ICT uses custom bed-of-nails fixtures to contact predefined test points on PCBs, verifying electrical parameters of each component with >95% fault coverage.

Test Items Include:

• Short/open circuit tests
• Resistance, capacitance, and inductance measurements
• Diode/transistor polarity verification
• IC power current checks
• Connector continuity tests

Equipment Configuration:

• Test channels: 512-2048
• Measurement accuracy: 0.1%-0.5%
• Test voltage: 5V-250V
• Test speed: 3-10 seconds/board

Economic Analysis: Fixture costs ~$5,000-$20,000, suitable for stable designs with monthly production >5,000 units, typically achieving ROI in <6 months.

4. Flying Probe Test

Flying probe testers use 4-8 programmable moving probes instead of traditional fixtures, ideal for low-volume, high-mix production.

Technical Features:

• Test coverage: Up to 98%
• Minimum test pitch: 0.2mm
• Test speed: 30-120 seconds/board (complexity-dependent)
• Capacitance range: 0.1pF-100μF
• Resistance accuracy: ±0.5%

Aplicaciones típicas:

• New product prototype verification
• High-reliability boards (military/aerospace)
• Low-volume premium products (medical devices)
• Development phases with frequent design changes

Latest Advancements: Modern flying probe testers integrate 3D laser height measurement for inspecting coplanarity, solder paste thickness, and other mechanical characteristics.

5. Automated X-ray Inspection (AXI)

AXI leverages differential X-ray absorption by materials to inspect hidden solder joints like BGAs and QFNs.

Detection Capability Matrix:

Equipment Selection Guide:

• 2D AXI: For simple BGA inspection, ~$150,000
• 3D AXI: Layer-by-layer imaging, from $300,000
• CT scanning: 3D volumetric data for failure analysis, >$500,000

6. Burn-in Test

Burn-in screens early failures through accelerated stress conditions. Common methods include:

Temperature Cycling: -40°C~+125°C, 50-100 cycles
High-Temperature Burn-in: 125°C powered operation for 96 hours
Voltage Stress: 1.5× rated voltage for 48 hours
Humidity Test: 85°C/85%RH for 1000 hours

Data Analysis: Weibull distribution models predict product lifespan, typically requiring MTBF>100,000 hours.

7. Functional Test (FCT)

FCT simulates real operating environments to validate complete board functionality. Test systems typically include:

• Programmable power supplies (0-30V/0-20A)
• Digital multimeters (6.5-digit precision)
• Function generators (100MHz bandwidth)
• Digital I/O modules (64-256 channels)
• Load banks (simulating actual loads)

Test Development Essentials:

1. Create test plans based on product specifications
2. Design test fixtures and interface adapters
3. Develop automated test scripts (LabVIEW/Python)
4. Establish pass/fail criteria
5. Integrate data traceability systems

8. Boundary Scan Test

Based on the IEEE 1149.1 standard, utilizes chips’ built-in test circuits to check interconnects, especially suitable for high-density boards.

Ventajas:

• No physical test points needed
• Can test the BGA bottom pins
• Supports Flash programming and CPU debugging
• Achieves ~85% test coverage

Typical Toolchain:

• BSDL file validation
• Test vector generation
• Result analysis software
• System-level test integration

Five Common PCB Testing Challenges & Solutions

Q1: How to balance test costs with quality requirements?

A: Implement tiered testing—basic AOI+FCT for all boards, add AXI sampling (10-20%) for critical products, and 100% inspection for military/medical applications. Statistics show this combination maintains defect escape rates <200ppm while keeping testing costs under 5% of total product cost.

Q2: Should low-volume production use ICT or flying probe testing?

A: Flying probe is more economical for batches <500/month. Actual cases show that for 300-unit/month orders, flying probe total costs (depreciation + labor) are about 1/3 of ICT, with product changeover time reduced from 8 hours to 30 minutes.

Q3: How to effectively inspect BGA solder quality?

A: Recommended three-stage approach: 3D AXI for solder shape/bridging, boundary scan for electrical connectivity, then functional test for actual performance. A telecom equipment manufacturer reduced BGA failure rates from 1.2% to 0.05% using this method.

Q4: How to reduce false test failures?

A: Control false alarm rates below 2% by:

1. Optimizing AOI algorithm parameters
2. Creating dynamic reference templates
3. Implementing machine learning classifiers
4. Adding verification stations for suspicious results
5. Regular equipment calibration

Q5: How to use test data for process improvement?

A: Establish test data traceability systems with key steps:

1. Assign unique IDs to each PCB
2. Record all raw test data
3. Perform CPK analysis using Minitab
4. Create SPC control charts for key parameters
5. Hold regular quality improvement meetings

Conclusión

PCB test is to ensure the reliability of electronic products is a key link, and needs to be based on product characteristics, production scale, and cost budget to design a reasonable test program. Through the scientific and systematic testing strategy, enterprises can control the PCB failure rate of 50 parts per million or less, which can enhance the competitiveness of the product market and brand reputation!