SAC305 solder
Tin–silver–copper solder selection across paste, wire, and bar forms, with product-specific thermal, flux, storage, and safety limits.
Tags: consumables, soldering, solder-alloys, electronics
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Indium lists Indalloy 256 (SAC305) at 217°C solidus and 220°C liquidus, with nominal 96.5% Sn, 3.0% Ag and 0.5% Cu by mass. Reflow peak, time above liquidus and residue acceptance depend on the paste formulation and assembly. Qualify them separately from the alloy melting interval. Indium solder-alloy reference
Alloy identity and scope
Indium supplies solder alloys as paste, preforms, wire, bars and spheres. Specify the physical form and flux system for the actual heating process. Indium solder-alloy reference
A useful purchasing description includes manufacturer/product, alloy, form, diameter or powder type, flux formulation/classification, package, shelf-life conditions, and applicable assembly requirements. SAC305 alone does not identify a flux or a qualified thermal profile. For example, MG Chemicals sells both 4900 resin-flux-cored wire and 4900P paste; they are different consumables despite sharing the alloy designation. MG 4900 wire, MG 4900P paste
Form and flux are separate decisions
| Form | Selection consequence | Bounded example |
|---|---|---|
| Flux-cored wire | Wire diameter and flux core accompany the metal; specify both for hand or automated wire-fed work. | MG 4900-227G is listed as a 227 g spool, 0.81 mm diameter, with 2.2% flux core. |
| Paste | Metal powder is dispersed in flux; printing/dispensing and reflow depend on the formulation. | MG 4900P is a no-clean paste for electronic assembly, including copper OSP surfaces. |
| Solid bar | A solder bath needs a separately selected flux and bath-control process. | ALPHA VACULOY SAC305 is offered for wave and selective soldering. |
MG identifies the 4900 wire's synthetic resin flux as REL0 under J-STD-004B. Its product claims about nonconductive and noncorrosive residues apply to that product; they are not properties conferred by the SAC305 metal composition. MG wire specification, MG paste overview, ALPHA VACULOY technical sheet, September 6, 2023
Thermal processing: melting is only one boundary
Kester's NP505-HR technical sheet, issued October 20, 2021, gives a starting convection profile with 235–250°C peak, typical 45–90 seconds in its labeled reflow zone, and a ramp below 2.5°C/s. It explicitly says the final profile depends on board mass and component combination. Do not turn the graph into a universal SAC305 recipe, equate its reflow-zone label with a separately defined time-above-liquidus specification, or assume an oven controller reading is the temperature of every joint. Kester NP505-HR profile
Wave and selective soldering use different process conditions. The ALPHA VACULOY sheet recommends 255–265°C solder-pot temperature for wave soldering and 280–320°C for selective soldering with its listed SAC alloys. These are bath recommendations for that product/process, not reflow peaks or iron-tip settings. The sheet also identifies copper-depleted replenishment alloys used when process conditions require correction of bath copper content. Maintain the specified bath chemistry rather than assuming additions of any SAC-family bar are equivalent. ALPHA application guidelines
Residues, cleanliness, and reliability
“No-clean” describes a formulation intended to leave acceptable residues under its specified process; it is not a statement that every assembly can skip cleaning. Kester says NP505-HR residues are designed to remain after reflow and provides for automated cleaning when removal is required. Its sheet reports surface-insulation-resistance and electrochemical-migration tests under named humidity, temperature, voltage, and duration conditions. Those tests do not establish unlimited field life, compatibility with every coating, or acceptance of an improperly reflowed residue. Kester residue and reliability data
MG's 4900P TDS, October 2, 2025, version 4.0, separately identifies ROL0 flux, 88% metal loading, and specified corrosion and insulation tests. Metal loading is the proportion of metal in paste, not the silver percentage of the metal alloy. Preserve that distinction when comparing paste specifications or calculating deposited material. Product-level test results should remain attached to the formulation and test method instead of being presented as generic SAC305 performance. MG 4900P technical data
Storage and handling
For 4900P, MG specifies storage at 2–10°C, upright with the syringe tip down, to limit flux separation and trapped air. Its 2025 TDS gives unopened-container shelf life of 3.5 years at 2–10°C or one year at 20–25°C, and directs users to let refrigerated paste reach room temperature before use. These limits belong to 4900P; transferring them to another SAC305 paste, opened material, or wire is unsupported. Retain the label and lot information and check the supplier's current instructions for the purchased package. MG 4900P storage instructions
Safety and compliance boundaries
Lead-free does not mean hazard-free or chemically pure. The ALPHA sheet specifies maximum lead of 0.07%, with an ultra-low-lead version at 0.05% maximum. Use the actual product declaration and applicable requirements when evaluating compliance; an alloy nickname alone does not establish the compliance of an entire assembly. ALPHA composition limits
The live UK 4900P SDS is version 4.00, revised May 12, 2026. It identifies serious eye irritation, suspected reproductive toxicity, possible nervous-system damage from prolonged/repeated exposure, and aquatic toxicity. These are formulation-specific hazards: use the current regional SDS, appropriate exposure controls and protection, and specified waste handling. The SDS expressly advises against high-temperature torch soldering/brazing or torch welding. Neither the term solder nor a lead-free label authorizes substituting a brazing process. MG 4900P UK SDS