What Is SAC305?
SAC305 is the industry-standard lead-free solder alloy. The name is an acronym of its composition:
| Element | Symbol | Percentage | Role |
|---|---|---|---|
| Tin | Sn | 96.5% | Base metal — forms the bulk of the solder joint. Provides wetting and electrical conductivity. |
| Silver | Ag | 3.0% | Strengthening element — improves mechanical strength and thermal fatigue resistance. |
| Copper | Cu | 0.5% | Reduces copper dissolution from PCB pads and component leads. Slows intermetallic growth. |
The key physical properties compared to traditional Sn63/Pb37 (leaded) solder:
| Property | SAC305 | Sn63/Pb37 |
|---|---|---|
| Melting point (liquidus) | 217-220°C | 183°C |
| Reflow peak temperature | 235-250°C | 205-225°C |
| Tensile strength | ~50 MPa | ~40 MPa |
| Shear strength | ~35 MPa | ~28 MPa |
| Thermal fatigue resistance | Better | Good |
| Wetting | Good (requires active flux) | Excellent |
| Joint appearance | Duller, grainy surface | Bright, shiny surface |
| RoHS compliant | ✅ Yes | ❌ No (contains lead) |
SAC305 became the de facto global standard after the EU RoHS directive (2006) banned lead in most consumer electronics. Today, it is used in virtually all commercial electronics manufacturing except for exempted applications (aerospace, military, medical implantables where leaded solder is still permitted for reliability reasons).
Why SAC305 — Not SAC105 or SAC405?
Several SAC variants exist, each with different silver content:
| Alloy | Silver % | Characteristics |
|---|---|---|
| SAC105 | 1.0% | Lower cost, lower strength. Used in low-cost consumer electronics. Poor drop-shock resistance. |
| SAC305 | 3.0% | The industry standard. Balanced strength, thermal fatigue, and wetting. Best all-around choice. |
| SAC387 | 3.8% | Higher strength, higher cost. Used in automotive and high-reliability. Near-eutectic (narrow melting range). |
| SAC405 | 4.0% | Highest silver content — maximum strength, highest cost. Used in extreme environments. |
SAC305 is the best value-for-performance alloy for general PCBA manufacturing. The 3.0% silver content provides sufficient mechanical strength for most applications without the cost premium of SAC405. The 0.5% copper minimizes copper dissolution from pads — important for fine-pitch and small-pad designs where pad integrity is critical.
Our Solder Materials — Original Manufacturer, Never Recycled
The quality of a solder joint depends as much on the quality of the solder material as on the reflow profile. Impurities in recycled solder — lead contamination, oxidized metal, inconsistent alloy composition — cause unreliable joints that pass initial testing but fail prematurely.
At Superb Automation, we source solder materials exclusively from original manufacturers:
Solder Paste
Alloy: SAC305 (Sn96.5/Ag3.0/Cu0.5)
Source: Original manufacturer — not recycled, not reclaimed, not re-blended
Particle size: Type 3 (25-45µm) for general SMT; Type 4 (20-38µm) for fine-pitch (<0.5mm pitch="">
Flux type: No-clean, ROL0 (Rosin, Low activity, Halide-free) per J-STD-004
Batch traceability: Every jar of paste is logged with manufacturer lot number. If a solder-related defect pattern emerges, we can trace it to a specific batch.
Solder Bar (Wave Soldering)
Product: ECO SOLDER BAR M24AQ — Senju Metal Industry (Japan)
Alloy: SAC305
Form: Solid bar, ~350g per bar
Purity: Virgin alloy from original manufacturer. No recycled content.
Dross rate: Low — the M24AQ formulation is designed for reduced dross (oxide) formation in wave soldering, extending pot life and reducing material waste.
Why "Original Manufacturer" Matters
The electronics supply chain has a problem with counterfeit and recycled solder. Solder bars and paste from unknown sources may contain:
Lead contamination: Recycled solder often contains residual lead from mixed waste streams. Even 0.01% lead contamination can cause a RoHS compliance failure.
Inconsistent alloy: Recyclers blend multiple solder sources. The resulting alloy may deviate from SAC305 specification, changing the melting point and mechanical properties.
Oxidized metal: Re-melted solder picks up oxides that create solder balls, poor wetting, and weak joints.
Using original manufacturer materials eliminates these risks. Every batch is certified to composition, particle size, and flux activity by the manufacturer. We maintain certificates of conformance for all solder materials — available to customers on request.
SAC305 Reflow Profile at Superb
The reflow profile for SAC305 is more demanding than leaded solder. The higher melting point means a narrower process window between "fully melted" (217°C) and "component damage" (typically 260°C maximum for most ICs).
Our standard SAC305 reflow profile (TEA-1200-DH 10-zone oven, nitrogen atmosphere):
| Phase | Temperature | Duration | Purpose |
|---|---|---|---|
| Preheat | 25°C → 150°C | 60-120 sec | Gradual ramp; prevents thermal shock |
| Soak | 150°C → 180°C | 60-120 sec | Flux activation; oxide removal |
| Reflow | Above 217°C | 45-75 sec | Solder melting and wetting |
| Peak | 235-245°C | 10-20 sec | Maximum temperature — intermetallic formation |
| Cooling | 245°C → 100°C | Controlled ramp | Fine grain structure; prevent thermal shock |
Time above liquidus (TAL): 45-75 seconds. Peak temperature: 235-245°C for most assemblies. The profile is verified with a sacrificial profiler board for every new board design and periodically re-verified for production boards.
SAC305 and RoHS Compliance
SAC305 is fully RoHS compliant (lead-free by definition). Combined with RoHS-compliant PCB surface finishes (ENIG, immersion silver, immersion tin, or OSP — we do not use HASL with lead), the finished assembly meets EU RoHS Directive 2011/65/EU requirements.
For customers who still require leaded solder (Sn63/Pb37) — typically aerospace/defense applications with RoHS exemptions or legacy designs — we can accommodate on request with segregated tooling and dedicated solder pots to prevent cross-contamination.
