Introduction
Copper strip temper is one of the most critical yet often overlooked variables in SMT lead frame manufacturing. The temper designation — half-hard, full-hard, or spring temper — directly determines the strip’s mechanical behavior during progressive die stamping: how easily it forms, how much it springs back, and how much wear it imposes on tooling. For procurement and process engineers sourcing bare copper strip in Southeast Asia, understanding temper selection means the difference between consistent high-yield stamping and costly die rework.
Understanding Copper Strip Temper Designations
What Temper Actually Means
Temper refers to the degree of cold working applied to copper strip after the final a
ealing cycle. As copper is rolled thi
er, its grain structure elongates and work-hardens, increasing strength and hardness while reducing ductility. The ASTM B152 / B152M standard defines standardized temper designations for copper and copper alloy strip.
Key Temper Grades for SMT Applications
| Temper | Hardness Range | Tensile Strength | Typical Application |
|---|---|---|---|
| Half-Hard (H02) | 60-80 HV | 240-300 MPa | Deep-drawn lead frames, complex bends |
| Full-Hard (H04) | 85-105 HV | 300-370 MPa | Standard SMT lead frames, moderate forming |
| Spring (H08) | 105-125 HV | 370-420 MPa | High-retention co
ectors, flat springs |
Half-Hard (H02): Best for Complex Forming
Half-hard copper strip retains approximately 50% of the cold work between a
ealed and full-hard conditions. It offers the best balance of formability and strength for lead frames requiring multiple bends, deep draws, or tight-radius features. The lower yield strength means less springback after stamping — typically 2-4 degrees for a 90° bend in 0.3mm thick strip — making it easier to hold tight dimensional tolerances.
However, half-hard strip generates more burr during blanking and punching due to its softer matrix. Progressive die clearance must be maintained at 4-6% of material thickness (versus 6-8% for full-hard) to minimize burr height. Tool maintenance intervals are typically 20-30% shorter compared to harder tempers.
Full-Hard (H04): The Industry Workhorse
Full-hard temper (also designated H04) is the most commonly specified temper for SMT lead frame stamping. It provides sufficient ductility for standard pin-forming operations while offering improved strength, better flatness, and reduced burr formation during high-speed stamping. Tensile strength in the 300-370 MPa range makes it suitable for most QFP, SOIC, and TSSOP lead frame designs.
Springback for a 90° bend in full-hard 0.25mm C11000 copper strip averages 5-8 degrees, which progressive die designers compensate for through over-bending features in the tooling. The moderate hardness also provides adequate wear resistance against the stamping die, extending tool life to 500,000-1,000,000 strokes between regrinds in well-maintained production environments.
Spring Temper (H08): Maximum Strength, Minimum Formability
Spring temper copper strip is cold-worked to near maximum hardness. With tensile strengths exceeding 370 MPa and elongation typically below 4%, this temper is reserved for applications where the strip functions as a mechanical spring element — such as battery contacts, SIM card co
ectors, and EMI grounding fingers — rather than a lead frame requiring significant forming.
The key challenge with spring temper is embrittlement risk. At hardness levels above 110 HV, copper strip becomes susceptible to edge cracking during blanking, especially when punch-to-die clearance falls below 6% of thickness. Progressive die design for spring temper requires larger clearance (8-10% of thickness) and polished punch/die surfaces to Rₐ ≤ 0.2 μm to prevent micro-crack initiation.
Temper Selection Decision Matrix
| Criterion | Half-Hard (H02) | Full-Hard (H04) | Spring (H08) |
|---|---|---|---|
| Bend radius capability | ≤ 0.5T | 0.5-1.0T | ≥ 1.5T |
| Springback (90° bend) | 2-4° | 5-8° | 10-15° |
| Burr tendency | Medium-High | Low-Medium | Low |
| Tool wear rate | High | Medium | Medium-High |
| Contact normal force | Low | Medium | High |
Procurement Considerations for Southeast Asian Manufacturers
When sourcing copper strip from regional suppliers, always request a temper certification per ASTM B152/B152M that includes measured Vickers hardness values, tensile test results, and grain size measurement per ASTM E112. Beware of “nominal temper” claims — actual hardness can vary ±10 HV within a lot. For high-volume SMT lead frame production, specify a hardness range of ±8 HV maximum to ensure consistent stamping behavior across coils.
Conclusion
Half-hard for complex forming, full-hard for general lead frame stamping, and spring temper for contact retention — each temper serves a distinct purpose in SMT electronics manufacturing. Matching the temper to the application geometry and production volume is not just a material specification exercise; it is a manufacturing cost optimization decision that affects die life, scrap rate, and ultimately per-unit lead frame cost.
