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Thu 25 Oct 2007, 19:00
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]](/articles/2007/10/25/CL2-45_nm_Penryn_Processors_will_be_100_Percent_Lead_Free/Intel-Getting_the_Lead_Out_presentation-sheet11-cropped-500x317.png "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]](/articles/2007/10/25/CL2-45_nm_Penryn_Processors_will_be_100_Percent_Lead_Free/Intel-Getting_the_Lead_Out_presentation-sheet14-cropped-500x219.png "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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