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Method and device to elongate a solder jointRelated Patent Categories: Metal Fusion Bonding, ProcessMethod and device to elongate a solder joint description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070114266, Method and device to elongate a solder joint. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICATION [0001] This application is a divisional of U.S. application Ser. No. 10/667,008, filed on Sep. 17, 2003. The disclosure of this prior application from which priority is claimed is incorporated herein by reference. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates generally to solder joints. More particularly, the present invention relates to a method and device to elongate a solder joint. [0004] 2. Description of the Related Art [0005] A solder joint is formed when a solder deposit between two substrates is subjected to reflow soldering. During reflow soldering, the solder deposit is heated such that it melts and wets a solderable surface on a substrate. The solder deposit solidifies upon subsequent cooling, forming the solder joint. [0006] Solder joints serve two functions in an electronic assembly; they provide mechanical support to hold various components in the electronic assembly together and electrical support to form electrical connections within a circuit. Examples of solder joints include chip-to-interposer connections such as controlled collapse chip connections (C4 joints), package-to-board connections in, for example, Surface Mount Technology (SMT), and chip-to-board connections such as in chip-on-board (COB) technology. [0007] During field application, the electronic assembly undergoes a temperature cycle each time it powers on or off. Due to differences in coefficients of thermal expansion (CTEs), substrates in the electronic assembly expand and contract to different degrees during the temperature cycle. This differential expansion and contraction of the substrates results in a movement of one end of a solder joint relative to another, which puts a strain on the solder joint. Because the electronic assembly undergoes numerous temperature cycles over its service life, the solder joints are subjected to repeated applications of strain, resulting in fatigue failure of the solder joints, which shortens the service life of the electronic assembly. [0008] Studies have shown that the fatigue life of a solder joint, that is, the number of applications of strain that a solder joint can sustain before fatigue failure, can be improved by elongating the solder joint. An elongated solder joint is more compliant and is therefore better able to absorb the strain caused by the temperature cycling. Consequently, various methods to elongate a solder joint have been proposed. [0009] One such method is disclosed in U.S. Pat. No. 4,545,610 issued to Lakritz, et al, wherein a solder extender on a substrate is positioned over a solder mound on a semiconductor chip and reflowed to form an elongated solder joint. A spacer is used to maintain a predetermined spacing between the semiconductor chip and the substrate. [0010] A drawback of this method is that it involves numerous processing steps. Each processing step increases the complexity of the manufacturing process and adds to the cost of production. In particular, the processing steps involving the use of vapour deposition techniques to form the solder extender on the substrate and then to deposit a layer of low melting metal onto a top surface of the solder extender make this method of elongating a solder joint expensive. [0011] In addition, because the probability of defects occurring in the solder joint increases with each processing step, the reliability of an elongated solder joint formed with this method is compromised. [0012] Another method for elongating a solder joint is disclosed in U.S. Pat. No. 5,968,670 issued to Brofman, et al. In this method, the solder joint is elongated when a spring, restrained in a compressed state by solder, is released during solder reflow. [0013] Unfortunately, this method also involves numerous processing steps which, as discussed previously, increase the complexity of the manufacturing process and the cost of production, and reduce the reliability of the solder joint. [0014] Additionally, because some of the components involved in this method are of an infinitesimal dimension, the handling of these components poses a problem. For example, it is difficult to manipulate the tiny spring into a suitable orientation for insertion into a minute cavity in a graphite boat mold to form an expandable solder bump. This difficulty in the handling of the components contributes to the complexity of the process. [0015] In view of the foregoing, it is desirable to have a method for elongating a solder joint that involves a minimal number of processing steps. It is also desirable to have a method that does not involve the handling of minute components. SUMMARY OF THE INVENTION [0016] The present invention fills these needs by providing a method and device to elongate a solder joint. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device or a method. Several inventive embodiments of the present invention are described below. [0017] One embodiment of the present invention provides a method to elongate a solder joint. The method begins by forming an elongator on a first substrate. The elongator comprises an expander and an encapsulant to encapsulate the expander. A solder joint is formed to connect the first substrate to a second substrate. Thereafter, the encapsulant is softened to release the expander from a compressed state to elongate the solder joint. [0018] The elongator may be formed on the first substrate by providing a mold having a first mold cavity and a second mold cavity. The first substrate is disposed in the first mold cavity, while an expander is disposed in the second mold cavity. The expander is compressed and an encapsulant is introduced into the mold to encapsulate the expander to form the elongator on the first substrate. [0019] The first substrate may be one of group consisting of a chip, an interposer, a package, a board, a series of interposers, a series of packages and a wafer. The first substrate may be subjected to singulation. [0020] The elongator may be formed on the first substrate by one of a group consisting of an injection molding process, a compression molding process, a transfer molding process and a casting process. [0021] The solder joint to connect the first substrate to the second substrate may be formed by melting a plurality of solder deposits to wet a solderable surface to form the solder joint. Continue reading about Method and device to elongate a solder joint... Full patent description for Method and device to elongate a solder joint Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method and device to elongate a solder joint patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Method and device to elongate a solder joint or other areas of interest. ### Previous Patent Application: Mesotube electode attachment Next Patent Application: Supporting device of a transport device of a soldering apparatus Industry Class: Metal fusion bonding ### FreshPatents.com Support Thank you for viewing the Method and device to elongate a solder joint patent info. 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