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45 nm Penryn Processors will be 100 Percent Lead-Free

Flip-chip bumps now built of copper columns and lead-free solder

October 25, 2007 - With the transition to the 45 nm process, Intel has officialy removed the last lead (Pb) from its manufacturing process. It has taken the chip manufacturer six years and over 100 million dollars to accomplish this. In 2008, the company will also transition its 65 nm chipset products to a 100 percent lead-free manufacturing process.

Lead has been used in electronics to form the electrical and mechanical connections between chip, package, and system circuitry. Finding suitable replacements for the lead/tin solder has been a technical challenge for the entire industry. Also, the huge number of components, the simultaneous availability, the reliability at higher temperatures, and the manufacturability at higher temperatures made this transition complex.

Chip Interconnects

The last lead in Intel's chip manufacturing process was part of the lead/tin solder in the flip-chip bumps. These First Level Interconnects (FLIs) connect the die through the package substrate with the underlying balls, leads, or pads.

Even though the Second Level Interconnects (2LIs) already had to be lead-free to comply with the RoHS legislation (Restriction of Hazardous Substances), there is an exemption for the FLI flip-chip bumps. By replacing the solder in the bumps with a tin/silver/copper alloy, Intel no longer requires the use of any exemptions.

The First Level Interconnects (FLIs) connect the die through the package substrate with the underlying balls, leads, or pads [Intel]

Copper Column

The use of lead-free solder increases stress during the manufacturing process. While the lead/tin solder requires a temperature of 183 °C, this temperature must be over 220 °C for lead-free solder. Since the package shrinks more than the die, the higher reflow temperature causes extra stress when heating and cooling the component.

Since the package shrinks more than the die, the higher reflow temperature causes extra stress when heating and cooling the component. [Intel]

To avoid the risk of cracks, solders containing lead have been replaced with a copper column and lead-free solder. Since copper is a better conductor than the previously used lead/tin solder, it also can carry more current.

Solders containing lead have been replaced with a copper column and lead-free solder. [Intel]

Other materials that had to be adjusted were the passivation (the material that seals the die surface and protects the underlying microcircuits), the flux (the material that helps forming a consistent solder bond in the reflow process), and the underfill (the adhesive epoxy between the die passivation and the solder metallurgy).

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