วิธีทดสอบ PCB: เปรียบเทียบ 7 วิธี [ICT, Flying Probe, FCT, AOI]

# วิธีทดสอบ PCB: เปรียบเทียบ 7 วิธี

การทดสอบ PCB และ PCBA เป็นขั้นตอนสำคัญในการรับประกันคุณภาพ บทความนี้เปรียบเทียบ 7 วิธีหลัก

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สารบัญ

1. ภาพรวมการทดสอบ
2. Visual Inspection
3. AOI
4. X-ray
5. ICT
6. Flying Probe
7. FCT
8. Burn-in
9. ตารางเปรียบเทียบ

---

ภาพรวมการทดสอบ {#overview}

```

PCB/PCBA Test Flow

═══════════════════════════════════════════════════════════

PCB Fabrication Stage:

├── Electrical Test (E-Test) ─────► Opens/shorts on bare PCB

└── Visual/AOI ───────────────────► Surface defects

SMT Assembly Stage:

├── SPI (Solder Paste Inspection) ► Before reflow

├── Pre-reflow AOI ───────────────► After placement

├── Post-reflow AOI ──────────────► After reflow

└── X-ray (if BGA/QFN) ───────────► Hidden joints

Electrical Test Stage:

├── ICT or Flying Probe ──────────► Component values, shorts

└── FCT (Functional Test) ────────► Board function

Final Stage:

├── Burn-in (if required) ────────► Infant mortality

└── Final Visual ─────────────────► Cosmetic check

═══════════════════════════════════════════════════════════

```

---

1. Visual Inspection {#visual}

Manual Visual Inspection

Limitations

• Human error
• Fatigue
• Not repeatable
• Cannot see hidden joints

---

2. AOI (Automated Optical Inspection) {#aoi}

```

AOI Capabilities

═══════════════════════════════════════════════════════════

Detects:

├── Missing components

├── Wrong components

├── Polarity errors

├── Tombstoning

├── Solder bridges

├── Insufficient solder

├── Excess solder

├── Component shift

├── Solder balls (visible)

└── Foreign material

Cannot Detect:

├── BGA/QFN hidden joints ──────► Need X-ray

├── Component values ───────────► Need ICT

├── Functional problems ────────► Need FCT

└── Internal cracks ────────────► Need X-ray

═══════════════════════════════════════════════════════════

```

AOI Specifications

---

3. X-ray Inspection {#xray}

When X-ray is Required

```

X-ray Required Components

═══════════════════════════════════════════════════════════

Always Need X-ray:

├── BGA (Ball Grid Array)

├── QFN (Quad Flat No-lead)

├── LGA (Land Grid Array)

├── CSP (Chip Scale Package)

└── Hidden solder joints

Recommended:

├── High-reliability products

├── Medical Class II/III

├── Aerospace

├── Automotive safety-critical

└── BGA rework verification

═══════════════════════════════════════════════════════════

```

X-ray Defect Detection

---

4. ICT (In-Circuit Test) {#ict}

How ICT Works

```

ICT Test Fixture

═══════════════════════════════════════════════════════════

┌─────────────────────────────┐

│ Test Head │

│ ┌─────────────────────┐ │

│ │ Spring Probes │ │

│ │ │ │ │ │ │ │ │ │ │ │

│ │ ▼ ▼ ▼ ▼ ▼ ▼ ▼ ▼ │ │

│ │ ┌─────────────────┐ │ │

│ │ │ │ │ │

│ │ │ PCB Under │ │ │

│ │ │ Test (UUT) │ │ │

│ │ │ │ │ │

│ │ └─────────────────┘ │ │

│ │ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ │ │

│ │ │ │ │ │ │ │ │ │ │ │

│ │ Bottom Probes │ │

│ └─────────────────────┘ │

└─────────────────────────────┘

ICT Tests:

├── Shorts/Opens

├── Resistance values

├── Capacitance values

├── Inductance values

├── Diode polarity

├── Transistor function

├── IC pin connections

└── Analog measurements

═══════════════════════════════════════════════════════════

```

ICT Pros & Cons

---

5. Flying Probe Test {#flying-probe}

Flying Probe vs ICT

```

Flying Probe Operation

═══════════════════════════════════════════════════════════

┌──────────────────────────────────────────────────┐

│ │

│ ╔═════╗ ╔═════╗ │

│ ║Probe║ ──────────────────────── ║Probe║ │

│ ║ 1 ║ PCB ║ 2 ║ │

│ ╚══╤══╝ ╚══╤══╝ │

│ │ ┌──────────────────┐ │ │

│ │ │ │ │ │

│ ├────► Test Points ◄───────┤ │

│ │ │ │ │ │

│ │ └──────────────────┘ │ │

│ ╔══╧══╗ ╔══╧══╗ │

│ ║Probe║ ║Probe║ │

│ ║ 3 ║ ║ 4 ║ │

│ ╚═════╝ ╚═════╝ │

│ │

└──────────────────────────────────────────────────┘

Typical: 4-8 probes moving independently

═══════════════════════════════════════════════════════════

```

Comparison: ICT vs Flying Probe

---

6. FCT (Functional Test) {#fct}

FCT Types

FCT Architecture

```

FCT Test System

═══════════════════════════════════════════════════════════

┌─────────────────────────────────────────────────────────┐

│ Test Controller │

│ ┌──────────┐ ┌──────────┐ ┌──────────┐ ┌──────────┐ │

│ │ Power │ │ Signal │ │ Load │ │ Data │ │

│ │ Supply │ │ Gen │ │ Box │ │ Capture │ │

│ └────┬─────┘ └────┬─────┘ └────┬─────┘ └────┬─────┘ │

└──────┼────────────┼────────────┼────────────┼───────────┘

│ │ │ │

└────────────┴────────────┴────────────┘

│

▼

┌─────────────┐

│ UUT │

│ (Board) │

└─────────────┘

FCT Tests:

├── Power consumption

├── Voltage levels

├── Communication (UART, SPI, I2C)

├── Sensor readings

├── Motor control

├── Display output

├── User interface

└── Full system function

═══════════════════════════════════════════════════════════

```

---

7. Burn-in Test {#burnin}

Purpose

จำลอง aging เพื่อค้นหา early failures (infant mortality)

When Required

• Medical devices (Class II/III)
• Aerospace/Defense
• High-reliability industrial
• Automotive safety systems
• Server/Datacenter

---

ตารางเปรียบเทียบ {#comparison}

Summary Comparison

*For hidden joints only

**Depends on test program

Decision Guide

```

Test Method Selection Guide

═══════════════════════════════════════════════════════════

Volume < 100 units:

├── Visual + Flying Probe + FCT

└── X-ray if BGA

Volume 100-500 units:

├── AOI + Flying Probe + FCT

└── X-ray if BGA

Volume 500-5,000 units:

├── AOI + ICT + FCT

└── X-ray if BGA

Volume > 5,000 units:

├── Inline AOI + ICT + FCT

├── X-ray (sampling or 100%)

└── Consider Burn-in for high-rel

═══════════════════════════════════════════════════════════

```

---

คำถามที่พบบ่อย

Q1: ต้อง test ทุกวิธีไหม?

A: ไม่จำเป็น เลือกตาม:

• Minimum: AOI + FCT
• Standard: AOI + ICT/Flying Probe + FCT
• High-rel: All above + X-ray + Burn-in

Q2: Test coverage 100% ได้ไหม?

A: ไม่มีวิธีเดียวที่ได้ 100% ต้องผสมหลายวิธี:

• AOI: Visual defects
• ICT: Component values
• FCT: Function
• X-ray: Hidden joints

Q3: ICT fixture คุ้มค่าตั้งแต่กี่ชิ้น?

A: โดยทั่วไป:

• Fixture cost: $10K
• Flying probe: $5/board
• ICT: $0.50/board
• Break-even: ~2,000 boards

---

บทสรุป

> สรุปจากผู้เชี่ยวชาญ: "ไม่มี one-size-fits-all สำหรับ testing การเลือกวิธีต้องดู volume, budget, และ acceptable defect rate อย่าประหยัดเรื่อง test ถ้า application เป็น safety-critical" — Hommer Zhao

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บริการของเรา

PCB Thailand มีบริการทดสอบครบวงจร:

• AOI - 2D/3D inspection
• X-ray - BGA/QFN inspection
• ICT - High volume
• Flying Probe - Prototype/low volume
• FCT - Custom test development

ติดต่อเรา สำหรับ testing requirements

---

บทความที่เกี่ยวข้อง

• SMT Defects Troubleshooting
• IPC Standards Guide
• DFM Guide