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Solder Alloy

FlipChip offers several different solder alloys to mach your needs. By using pre-mixed solder paste and pre-formed solder balls, alloy composition is very tightly controlled. This means that your solder balls have predictable and reliable reflow characteristics.

Basic Physical Properties of Solder Paste Alloys

The SFC-Ball on I/O, SFC-Repassivation, and SFC-Redistribution processes use pre-mixed solder paste to form the final solder bumps. The table below gives the basic properties of the paste alloys.

Table 1. Physical Proprieties of Paste Alloys

Alloy / Property Sn/Ag/Cu Lead Free-2 (SAC 3.5) 63Sn37Pb Standard Eutectic 5Sn95Pb High Lead* 63Sn37Pb Low Alpha 63Sn37Pb Ultra Low Alpha
Alloy Composition Sn 95.5%
Ag 3.5%
Cu 1.0%		 Sn 63%
Pb 37%		 Sn 5%
Pb 95%		 Sn 63%
Pb 37%		 Sn 63%
Pb 37%
Melting 217°C Eutectic 183°C Eutectic 300°C - 314°C 183°C Eutectic 183°C Eutectic
Reflow Temperature 235°C to 255°C 215°C to 225°C 330°C to 340°C 215°C to 225°C 215°C to 225°C
Alpha Emissions (counts/cm2 /hr) <0.002 N/A N/A <0.02 <0.002

* Production Ready

Basic Physical Properties of Pre-Formed Solder Ball Alloys

The UltraCSP, Spheron, and Polymer Collar WLP processes use pre-formed solder balls. The standard solder ball sizes are 0.25mm (250µm), 0.3mm (300µm), 0.35mm (350µm), 0.4mm (400µm), and 0.5mm (500µm). The basic physical properties of the pre-formed solder balls are listed on the table below.

Table 2. Physical Proprieties of Pre-Formed Solder Ball Alloys

Alloy / Property Sn/Ag/Cu Lead Free (LF2) (SAC 2.6) 63Sn37Pb Eutectic 63Sn37Pb Low Alpha Eutectic 95Pb5Sn High Lead
Alloy Composition Sn 96.8%
Ag 2.6%
Cu 0.6%		 Sn 63%
Pb 37%		 Sn 63%
Pb 37%		 Sn 5%
Pb 95%
Melting Point 218°C - 220°C 183°C Eutectic 183°C Eutectic 308°C - 314°C
Reflow Temperature 235°C to 255°C 215°C to 225°C 215°C to 225°C 325°C to 335°C
Alpha Emissions
(counts/cm2 /hr)		 <0.002 N/A 0.02 N/A