SMD Resistor Code Calculator and Reference Guide

1. Code Types

SMD resistors use several marking systems:

• 3-digit numerical code (e.g., 103 = 10kΩ)
• 4-digit numerical code (e.g., 1002 = 10kΩ)
• EIA-96 code (e.g., 01A = 100Ω)
• Standard metric sizes (e.g., 0603, 0805)

2. Numerical Code System

For 3 and 4-digit codes:

• First two/three digits: Significant figures
• Last digit: Multiplier (number of zeros)
• Letter R: Decimal point (e.g., 4R7 = 4.7Ω)
• Examples: 472 = 4.7kΩ, 1001 = 1kΩ

3. EIA-96 Code System

The EIA-96 system provides 96 values per decade:

• First two characters: Value code (01-96)
• Last letter: Multiplier (A-Z)
• Higher precision than standard E24 series
• Common in precision applications

4. Size Codes

Common SMD sizes and their dimensions:

• 0201: 0.6mm × 0.3mm
• 0402: 1.0mm × 0.5mm
• 0603: 1.6mm × 0.8mm
• 0805: 2.0mm × 1.25mm
• 1206: 3.2mm × 1.6mm
• 2010: 5.0mm × 2.5mm

5. Power Ratings

Typical power ratings by size:

• 0201: 1/20W (0.05W)
• 0402: 1/16W (0.063W)
• 0603: 1/10W (0.1W)
• 0805: 1/8W (0.125W)
• 1206: 1/4W (0.25W)
• 2010: 3/4W (0.75W)

6. Design Considerations

When using SMD resistors, consider:

• PCB layout and thermal management
• Reflow soldering profile
• Power derating at temperature
• Voltage rating limitations
• Current handling capability
• Environmental protection needs

7. Temperature Coefficient of Resistance (TCR)

TCR is a critical parameter for SMD resistors that indicates resistance change with temperature:

• Standard TCR ranges: ±100 ppm/°C to ±200 ppm/°C
• Precision TCR ranges: ±25 ppm/°C to ±50 ppm/°C
• Ultra-precision TCR: ±5 ppm/°C to ±15 ppm/°C
• Temperature range: -55°C to +155°C typical

8. Tolerance Classifications

SMD resistors are available in various tolerance grades:

• Ultra-precision: ±0.1% (marked with 'B')
• Precision: ±0.5% (marked with 'D')
• Standard: ±1% (marked with 'F')
• General purpose: ±5% (marked with 'J')

9. Special Marking Systems

Additional marking systems used in specific applications:

• Military specification markings (MIL-PRF-55342)
• Automotive grade markings (AEC-Q200 qualified)
• High-reliability space grade markings
• Custom manufacturer-specific codes

10. Application Guidelines

Important considerations for SMD resistor selection:

• Operating temperature range requirements
• Maximum working voltage (MWV)
• Pulse handling capability
• Moisture sensitivity level (MSL)
• Board assembly requirements
• Cost vs. performance trade-offs

11. Reliability Factors

Key reliability parameters to consider:

• Failure rate (FIT - Failures In Time)
• Load life stability
• Moisture resistance
• Thermal cycling performance
• Solderability and terminal strength
• Environmental stress screening (ESS)

12. Industry Standards

Relevant standards for SMD resistors:

• JESD97 for marking codes
• IEC 60115-8 for dimensions
• AEC-Q200 for automotive
• MIL-PRF-55342 for military
• IECQ certification requirements
• RoHS and REACH compliance