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Reliable printed wiring board assembly employing packages with solder joints and related assembly techniqueRelated Patent Categories: Semiconductor Device Manufacturing: Process, Packaging (e.g., With Mounting, Encapsulating, Etc.) Or Treatment Of Packaged SemiconductorReliable printed wiring board assembly employing packages with solder joints and related assembly technique description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20080064139, Reliable printed wiring board assembly employing packages with solder joints and related assembly technique. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE AND PRIORITY CLAIM TO RELATED APPLICATION [0001] This application is a division of, claims priority to, and wholly incorporates by reference U.S. patent application Ser. No. 10/956,405 filed Sep. 30, 2004. FIELD OF THE INVENTION [0002] The present invention relates to semiconductor package assembly. More specifically, the invention relates to printed wiring board assembly techniques involving packages having solder bumps and other solder joints. BACKGROUND OF THE INVENTION [0003] Packaging arrangements employing solder bumps are known. Examples include ball grid arrays ("BGAs") and chip-scale packages ("CSPs"). By way of illustration, BGAs have a series of solder bumps (or "balls") typically arranged on the bottom of the package. The solder balls are used to attach the BGA package to a printed wiring board ("PWB") using a reflow technique. During the reflow process, the solder balls are melted, and upon melting, the solder balls electrically and mechanically join various of the BGA package traces to various of the system PCB traces. [0004] A PWB generally exhibits some degree of flexibility depending on its structural composition and its operating environment, whereas the packages mounted on the PWB remain relatively rigid by comparison. This difference can result in significant mechanical stresses being asserted between the PWB and the package, causing the physical connection between the package and the PWB to fail. An example of a severe failure is when the solder ball is disconnected from a corresponding contact on the PWB, resulting in an interruption of the connection between appropriate contacts of the package and the PWB. Such failures are typically remedied by way of expensive and time-consuming tear down and reassemble of the package and PWB, resulting in undesirable expense and inconvenience to both manufacturer and consumer. [0005] Existing approaches for resolving this problem have a number of drawbacks. For example, the use of expensive rigid boards significantly raises costs. In addition, such rigid boards typically employ insulating layers comprising epoxy and glass, which, among other problems, are difficult to drill, e.g., for forming vias. Consequently, assembly productivity is reduced. Another approach is to increase the size of the solder balls used to connect packages and PWBs. However, increasing the volume of the solder balls between the surface of the package and the PWB can result in bridging adjacent solder balls, thereby undesirably shorting contacts, which can result in malfunctions and/or damage. [0006] Accordingly, there remains a strong need in the art to provide a cost effective and reliable assembly for printed wiring board and packages employing solder joints. SUMMARY OF THE INVENTION [0007] An assembly for printed wiring boards and packages employing solder joints and related assembly technique are disclosed which address and resolve one or more of the disadvantages associated with conventional assembly arrangements, as discussed above. [0008] By way of illustration, an exemplary assembly comprises a printed wiring board having a first surface, and a package including a plurality of solder joints, such as solder balls, on one surface of the package. An anchor via is defined through the first surface of the printed wiring board, and conductive material situated in the anchor via is connected to or integral with a respective solder joint of the package. In one embodiment, the solder joint connected to the conductive material in the anchor via is situated proximate a periphery or corner of the package. As discussed below, the particular arrangement of this assembly significantly improves reliability. [0009] Other features and advantages of the present invention will become more readily apparent to those of ordinary skill in the art after reviewing the following detailed description and accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS [0010] FIG. 1 illustrates an exemplary assembly employing a package with solder balls according to one embodiment of the present invention. [0011] FIG. 2 illustrates a sectional view of the exemplary assembly of FIG. 1. [0012] FIGS. 3A through 3D illustrate exemplary assembly arrangements according to various stages of assembly according to one embodiment of the present invention. [0013] FIG. 4 illustrates an exemplary assembly employing a package with solder balls according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION [0014] The drawings and their accompanying detailed description are directed to merely exemplary embodiments of the invention. To maintain brevity, other embodiments of the invention which use the principles of the present invention are not specifically described herein and are not specifically illustrated by the present drawings. It is noted that, for ease of illustration, the various elements shown in the drawings are not drawn to scale. [0015] Referring first to FIG. 1, there is shown a top view of exemplary assembly 100 including PWB 102 and package 104 according to one embodiment of the invention. PWB 102 comprises a multi-layer wiring board. For example, PWB 102 may comprise a plurality of conductive layers, typically metal, each conductive layer being separated by a dielectric layer, typically epoxy. Package 104 is mounted on surface 103 of PWB 102. In certain embodiments, PWB 102 is capable of receiving a plurality of packages, e.g., two or more packages on the same surface or one package on a top surface and a second package on a bottom surface. [0016] Package 104 may be any package having a plurality of solder joints, such as solder balls, for attaching to PWB 102. When mounted on PWB 102, the solder joints provide an electrical connection and a conductive path between elements of package 104 and elements attached to PWB 102, such as a supply voltage or a reference voltage, for example. In addition, the solder joints mechanically attach package 104 to PWB 102. [0017] In an example embodiment where package 104 employs solder balls, package 104 is typically attached to PWB 102 using a reflow process, whereby the solder balls are melted, and upon melting, the solder balls are mechanically and electrically attached to corresponding bump attach sites on PWB 102. By way of illustration, bump attach sites 106a through 106e, and 121 are depicted and referenced in FIG. 1. Generally, bump attach sites comprise a metal layer formed and patterned on surface 103 of PWB 102. Certain bump attach sites are also connected to electrical traces formed on surface 103 for routing electrical signals to other elements (not shown). For example, bump attach site 106d is connected to electrical trace 107. Other bump attach sites, such as bump attach site 106c and 121 are electrically connected to intermediate metal layers of PWB 103 or other metal layers on a surface (such as an opposite surface to surface 103, for example) of PWB 102. For example, bump attach site 106c and 121 may be connected to an intermediate metal layer by way of interconnect vias 120 and 122, respectively. [0018] Interconnect vias 120 and 122 are generally formed by drilling through bump attach site 106c and 121, respectively, and through a dielectric layer below bump attach sties 106c and 121 to the intermediate metal layer. Interconnect vias 120 and 122 are subsequently filled or plated with conductive material for providing an electrical connection between bump attach sites 106c and 121 and their respective intermediate metal layer. The respective intermediate metal layers are then electrically connected to respective elements, typically through other traces and other metal interconnects. Continue reading about Reliable printed wiring board assembly employing packages with solder joints and related assembly technique... 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