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Electrical circuit apparatusRelated Patent Categories: Metal Fusion Bonding, ProcessElectrical circuit apparatus description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070119904, Electrical circuit apparatus. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The present application is a divisional patent application of and claims priority to co-pending U.S. patent application having Ser. No. 11/180,188 filed Jul. 13, 2005 by Waldvogel, et al., and titled "ELECTRICAL CIRCUIT APPARATUS AND METHOD FOR ASSEMBLING SAME". FIELD OF THE INVENTION [0002] The present invention relates generally to an electrical circuit apparatus, wherein components are mounted to a circuit board, and have a lower coefficient of thermal expansion than the heat sink to which they are coupled. BACKGROUND OF THE INVENTION [0003] When constructing power amplifiers various components or devices (wherein the terms component and device is used interchangeably herein) must be mounted to a circuit board or substrate. Many of these components are mounted to a top side of the circuit board using a known solder reflow process. For instance, a load resistor having at least one input terminal and having a ground portion (also referred to herein as a ground flange or a ground terminal, wherein these terms may be used interchangeably) may be mounted to the top side of the circuit board. When mounting a load resistor to a circuit board, three factors must be balanced. First, the load resistor must have a proper and sufficient electrical connection to the circuit board, wherein the input terminals are soldered to the top side of the circuit board and the ground terminal is sufficiently coupled to a heat sink that is typically soldered locally to the underside of the circuit board in an area primarily surrounding the load resistor. In addition, a sufficient thermal conduction path must be established between the load resistor and the heat sink. Moreover, load resistors are typically made of a ceramic material, which presents a thermal expansion mismatch between the load resistor and the heat sink since the heat sink typically has a higher coefficient of thermal expansion (CTE) than the ceramic load resistor. This CTE mismatch can result in local distortion or warping of the circuit board after assembly. Solder joint reliability can also be significantly degraded in a thermal cycling application. [0004] There are a number of methods used for mounting devices such as load resistors to a circuit board, including a hybrid manufacturing process using fixtures (i.e., a one pass solder reflow process) and a two pass solder reflow process. The hybrid manufacturing process is typically associated with ceramic circuit boards and possibly with carrier plates that serve as heat sinks. Due to the fragility of the substrate, large fixtures are usually required for its alignment and protection during processing. The use of fixtures usually forces manual processing. [0005] One disadvantage of the hybrid manufacturing process is that it is more costly than other manufacturing methods primarily due to the added cost of the fixtures used in the process and also due to the need for a number of manual steps that generate a lower production throughput. An additional disadvantage is that manufacturing with fixtures produces a significant variation in part placement and solder attachment due to fixture tolerances or due to fixture degradation with repeated use. [0006] Turning now to the two pass solder reflow process. During the first pass of the solder reflow process, a plurality of heat sinks are locally coupled to the ground layer of a circuit board in areas primarily surrounding where power components will be mounted. Thereafter, solder is placed in strategic areas on the board, and a plurality of components, including, load resistors, are mounted onto and soldered to the board in a second pass of the reflow solder process. [0007] A primary disadvantage of the two pass reflow process is that it requires one high-temperature reflow pass with a high melting temperature solder alloy, and a second subsequent reflow pass with a lower melting temperature solder allow. The first pass exposes the circuit board to high temperature, which can result in damage such as distortion. The requirement of two independent passes with different solder temperature settings limits manufacturing throughput. The two pass approach also does not lend itself well to no-lead solder because the first temperature needed to attach the heat sinks would have to exceed the elevated no-lead solder reflow temperature. This is a significant disadvantage because no-lead solder attachment may likely become a key product differentiator in the near future since some markets, especially European markets, are moving toward requiring no-lead solder attachment. [0008] In addition, neither the hybrid manufacturing process nor the two pass solder reflow process addresses the thermal expansion mismatch issues that arise when mounting devices such as ceramic load resistors to a circuit board. [0009] Thus, there exists a need for a cost effective electrical circuit apparatus wherein: components may be mounted to a circuit board without the need for fixtures; the process for assembling the electrical circuit apparatus is compatible with a single pass solder reflow process that is compatible with, but is not limited to no-lead solder; and any thermal expansion mismatch problems in the electrical circuit apparatus are addressed and, when possible, minimized. BRIEF DESCRIPTION OF THE DRAWINGS [0010] The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention. [0011] FIG. 1 illustrates a topside view of a schematic diagram of a portion of a substrate in accordance with embodiments of the present invention; [0012] FIG. 2 illustrates a topside view of a schematic diagram of an adhesive layer in accordance with embodiments of the present invention; [0013] FIG. 3 illustrates an exploded view of electrical circuit apparatus including a heat sink, an adhesive layer, a substrate, and components in accordance with embodiments of the present invention; [0014] FIG. 4 illustrates a flow diagram of a method for assembling an electrical circuit apparatus in accordance with embodiments of the present invention; [0015] FIG. 5 illustrates an assembled topside view of electrical circuit apparatus in accordance with embodiments of the present invention; [0016] FIG. 6 illustrates a cross-sectional view at a section A-A of the electrical circuit apparatus illustrated in FIG. 5 prior to solder wetting; [0017] FIG. 7 illustrates a cross-sectional view at a section A-A of the electrical circuit apparatus illustrated in FIG. 5 subsequent to solder wetting; and [0018] FIG. 8 illustrates an X-Ray image depiction of an assembled electrical circuit apparatus in accordance with embodiments of the present invention after device population and reflow soldering. DETAILED DESCRIPTION OF THE INVENTION [0019] Before describing in detail embodiments that are in accordance with the present invention, it should be observed that the embodiments reside primarily in combinations of method steps and apparatus components related to a method and apparatus for an electrical circuit assembly. Accordingly, the apparatus components and method steps have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. Thus, it will be appreciated that for simplicity and clarity of illustration, common and well-understood elements that are useful or necessary in a commercially feasible embodiment may not be depicted in order to facilitate a less obstructed view of these various embodiments. [0020] In this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises . . . a" does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element. Continue reading about Electrical circuit apparatus... Full patent description for Electrical circuit apparatus Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Electrical circuit apparatus 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. 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