Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Configuration or pattern of bonds
Reexamination Certificate
2000-08-31
2001-10-30
Clark, Sheila V. (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Configuration or pattern of bonds
C257S777000, C257S780000, C257S778000, C438S110000
Reexamination Certificate
active
06310403
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to electronics, in general, and to substrate assemblies, in particular.
BACKGROUND OF THE INVENTION
Many electronic components are comprised of different substrates that are assembled together. Typically, each substrate has a different Coefficient of Thermal Expansion (CTE). As an example, an electronic component can include a semiconductor substrate or chip mounted on an organic substrate. The CTE difference between the chip and the organic substrate is on the order of 15 parts per million per degree Celsius (ppm/° C.). Bond pads of the chip should be aligned to bond pads of the organic substrate at room temperature, but the large difference in thermal expansion produces a thermal mismatch at a solder reflow temperature that can cause significant misalignment of the bond pads of the chip and the organic substrate.
Interconnect bumps such as solder balls are typically used to electrically connect the bond pads of the chip to the bond pads of the organic substrate, but the thermal mismatch between the chip and the organic substrate distorts the shape and height of the solder balls. The irregular shape and height of the solder balls increases the localized tensile stress within the solder balls at an interface between the solder balls and the bond pads. Experiments have shown that this stress can produce cracks within a solder ball, within a bond pad, and at the interface between a solder ball and a bond pad. These cracks significantly degrade the reliability of the component. Other experiments have shown that the thermal mismatch problem and the reliability problem increase in severity as the size of the chip and the organic substrate increases.
The solder balls used to electrically connect the bond pads are typically comprised of a lead-based solder such as, for example, tin lead solder. These leadbased solders have melting temperatures generally above 180° C. These lead-based solders, however, are toxic. Replacing these lead-based solders with lead-free solders makes the components safer, but also increases the thermal mismatch and reliability problems because the lead-free solders have melting temperatures generally above 220° C. The higher melting temperatures of the lead-free solders increase the severity of the thermal mismatch problem, which degrades the reliability of the components even further due to the increased possibility of interconnect cracking.
Accordingly, a need exists for a method of manufacturing components and a component thereof that reduces the localized tensile stress within the interconnect bumps.
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A. Beikmohamadi et al.—DuPont Co. & G. Hotchkiss et al. —Texas Instruments, Inc., “Tacky Dots™ Technology for Flip Chip and BGA Solder Bumping”, IEEE, Jun. 1998.
Guo Yifan
Li Li
Lin Jong-Kai
Lindsey Scott E.
Zhang Chunsheng
Clark Sheila V.
Motorola Inc.
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