Patent Publication Number: US-2004041002-A1

Title: Alignment weight for floating pin field design

Description:
[0001] This application is a continuation of U.S. patent application Ser. No. 09/754,714, filed Jan. 4, 2001, which is a divisional of U.S. patent application Ser. No. 09/288,486, filed Apr. 8, 1999, which is now U.S. Pat. No. 6,206,272, which are incorporated herein by reference. 
    
    
     
       TECHNICAL FIELD OF THE INVENTION  
       [0002] Embodiments described herein relate generally to the field of electronic circuits and, in particular, to an alignment weight for an electronic circuit with a floating pin field design.  
       BACKGROUND  
       [0003] Integrated circuits are a common part of modern electronic equipment. Integrated circuits typically include a large number of transistors and other circuit elements that are interconnected on a common semiconductor chip or die. Typically, integrated circuits are packaged independently and interconnected on a printed circuit board for installation in an electronic system, such as a computer.  
       [0004] A printed circuit board can be connected to an electronic system in a number of ways. For example, a printed circuit board can include a “floating pin field” on one side of the printed circuit board. The floating pin field includes a number of pins that are held in a fixed spatial relation by a pin field carrier through which the pins pass. The pins are electrically connected to circuit elements on the printed circuit board. A floating pin field design may be used, for example, with a printed circuit board containing an upgraded processor for a computer.  
       [0005] When a floating pin field design is used, the printed circuit board may be connected to a system through a socket such as a socket located on a mother board of a computer system. The socket typically includes a number of receptacles that are placed around a perimeter of the socket. The receptacles receive the pins of the floating pin field.  
       [0006] One problem with printed circuit boards that use a floating pin field design may arise when pins are soldered to the bottom of the printed circuit board. Generally, the pins are held in place with a pin field carrier. The printed circuit board is patterned with solder paste at the locations where the pins are to connect to the printed circuit board. The pins and the pin field carrier are placed on the board and the solder undergoes a reflow process. Unfortunately, sometimes not all of the solder joints created with this reflow process provide acceptable connection between the pin and the circuit elements on the printed circuit board. So-called “solder bridges”—solder material that extends over a significant distance between a pin and the printed circuit board—can be formed, for example, when a pin moves away from the printed circuit board during the reflow process. These solder bridges provide a poor, brittle mechanical connection for the pin and can lead to open solder joints during use. Furthermore, when an open solder joint is detected after production, the part is typically thrown away since rework of the open solder joints is overly burdensome. This can result in a significant waste of resources when fabricating electronic modules using floating pin fields.  
       [0007] For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a more reliable technique for producing acceptable solder joints in an electronic module using a floating pin field design.  
       SUMMARY  
       [0008] The above mentioned problems with electronic modules using a floating pin field design and other problems are addressed by the various embodiments disclosed, as will be understood by reading and studying the following specification. An alignment weight is described that may be used to hold the pins in place during a reflow process.  
       [0009] In an embodiment, an alignment weight is provided. The alignment weight includes a body of material having first and second opposing surfaces. A number of depressions are formed in the first surface. The depressions receive pins of a floating pin field when placed on a floating pin field during connection of the floating pin field to a printed circuit board. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0010]FIG. 1 is a perspective view of an illustrative embodiment of an alignment weight according to the teachings of various embodiments.  
     [0011]FIG. 2 is a bottom view of the alignment weight of FIG. 1.  
     [0012]FIG. 3 is a cross-sectional view of a portion of an electronic module during production with an alignment weight in place according to various embodiments.  
     [0013]FIG. 4 is a perspective view of an electronic system module with a floating pin field constructed using the alignment weight according to various embodiments. 
    
    
     DETAILED DESCRIPTION  
     [0014] The following detailed description refers to the accompanying drawings which form a part of the specification. The drawings show, and the detailed description describes, specific illustrative embodiments. These embodiments are described in sufficient detail to enable those skilled in the art to practice the teachings disclosed herein. Other embodiments may be used and logical, mechanical and electrical changes may be made without departing from the scope of the disclosure. The following detailed description is, therefore, not to be taken in a limiting sense.  
     [0015]FIG. 1 is a perspective view of an alignment weight indicated generally at  100  and constructed according to the teachings of various embodiments. Alignment weight  100  is used in a process for connecting pins of a floating pin field to a printed circuit board. Specifically, alignment weight  100  is designed to provide a downward force that helps to secure pins in place during a solder reflow process and to maintain the pins in a substantially straight-up alignment. Advantageously, alignment weight  100  also maintains the ends of the pins of the floating pin field substantially in the same plane.  
     [0016] Alignment weight  100  is formed from a material that can withstand the heat of a solder reflow process without significant warping. Further, the material has sufficient weight to provide downward force on the pins to assure the creation of an acceptable solder joint. For example, in one embodiment, alignment weight  100  is formed from Ultem® PolyEtherImide material, e.g., Ultem®2300, commercially available from Ensiger Corporation. Ultem® PolyEtherImide is an amber transparent high performance polymer which combines high strength and rigidity at elevated temperatures with long term heat resistance. Other appropriate materials can be used to produce the body of alignment weight  100 .  
     [0017] Alignment weight  100  includes first and second opposing surfaces  104  and  106 , respectively. Surface  106  includes a number of depressions  108 . Depressions  108  are disposed in surface  106  in positions that correspond to the locations of pins in a floating pin field to be used with alignment weight  100 . In one embodiment, depressions  108  are disposed in rows around the perimeter of surface  106  as shown in FIGS. 1 and 2. However, it is understood that depressions  108  can be disposed at other locations on surface  106  so as to accommodate the layout of other floating pin field designs.  
     [0018] The size of depressions  108  may be selected to assure proper vertical alignment of the pins of the floating pin field. For example, when the pins have a diameter of approximately 0.01±0.001 inches, depressions  108  may be formed with an outer diameter at surface  106  of about 0.065 inches with an interior angle of 82 degrees and an inner diameter of about 0.055 inches.  
     [0019] Alignment weight  100  further includes holes  110  that extend through a thickness of alignment weight  100  in center region  107 . Holes  110  allow heat to flow through alignment weight  100  toward a printed circuit board located below alignment weight  100  during a reflow process. This allows elements other than pins to be soldered beneath the alignment weight when the pins are soldered in place.  
     [0020] In some embodiments, holes  110  are laid out in an array in center region  107 . However, it is understood that holes  110  can be located at other positions in alignment weight  100 . Further, holes  110  are shown as cylindrical passages through alignment weight  100 . Holes  110  can, however, have different sizes and shapes and are not limited to the embodiment shown. In some embodiments, the holes  110  can be omitted when only pins are soldered during a reflow process and no other elements are placed on printed circuit board  304  beneath alignment weight  100 .  
     [0021]FIG. 3 is a cross-sectional view of a portion of an electronic module  300  during production with alignment weight  100  in place according to various embodiments. Alignment weight  100  may be used to assure proper contact between pins  302  and printed circuit board  304  at solder contacts  306 . Advantagously, alignment weight  100  can be used to maintain the ends  314  of pins  302  in substantially the same plane. This reduces the likelihood that solder bridges will form at the base of any of pins  302 .  
     [0022] The pins  302  may be held in a fixed alignment by the field carrier  308 , which may be formed from flame retardant 4 (FR4) material with holes for receiving pins  302 . Field carrier  308  may hold the pins  302  in a position that is substantially normal to surface  307  of field carrier  308 . The floating pin field  310  may comprise the pins  302  and the field carrier  308 .  
     [0023] The floating pin field  310  may be placed in contact with screen printed solder paste on surface  312  of printed circuit board  304  at connection points for pins  302 . With the floating pin field  310  in place, alignment weight  100  may be placed over the ends  314  of the pins  302  such that depressions  108  align with the ends  314  of the pins  302 . Electronic module  300  along with alignment weight  100  may undergo a solder reflow process to form the contacts  306 . The alignment weight  100  may then be removed.  
     [0024] As shown in FIG. 4, additional circuit components  400  can be coupled to the printed circuit board  304  using, for example, surface mount technology. For example, an upgraded microprocessor can be coupled to the printed circuit board for insertion into a computer system on the printed circuit board  304 .  
     [0025] Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement which is calculated to achieve the same purpose may be substituted for the specific embodiments shown. Such applications are intended to cover any adaptations or variations of the various embodiments. For example, the alignment weight can be used with floating pin fields for electronic modules other than a processor upgrade. Further, the location, depth, diameter, and interior angle of the depressions  108  can be varied as necessary for a particular pin field. Further, the alignment weight  100  can be formed without holes  110 . Further, circuit components  400  can be coupled to both sides of the printed circuit board  304 . Other materials that are resistant to warping at elevated temperatures and that provide sufficient weight to aid in improving the solder bonds can be used for the alignment weight  100  in place of the Ultem® PolyEtherImide material described above. Other bonding materials can be used in place of solder to connect the pins  302  to the printed circuit board  304 .  
     [0026] This detailed description is not to be taken in a limiting sense, and the scope of various embodiments is defined only by the appended claims, along with the full range of equivalents to which such claims are entitled. Thus, although specific embodiments have been illustrated and described herein, it should be appreciated that any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. This disclosure is intended to cover any and all adaptations or variations of various embodiments of the invention. Combinations of the above embodiments, and other embodiments not specifically described herein, will be apparent to those of skill in the art upon reviewing the above description.  
     [0027] The Abstract of the Disclosure is provided to comply with 37 C.F.R. § 1.72(b), requiring an abstract that will allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing detailed description, it can be seen that various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments of the invention require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the detailed description, with each claim standing on its own as a separate preferred embodiment.