Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
1999-11-12
2002-11-19
Cuneo, Kamand (Department: 2827)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C228S180100, C361S773000, C174S263000
Reexamination Certificate
active
06483041
ABSTRACT:
BACKGROUND OF THE INVENTION
Some connection systems between electronic components such as printed circuit boards (PCBs), backplanes, cables, integrated circuits (ICs), IC connectors and the like, use metal pins and metallic, plated-through cylinders called vias. Often, such a system includes one electronic component which has a set of metal pins and another component which has a corresponding set of vias. In general, the component with the pins includes a housing which positions the pins such that the pins extend from the housing in a grid-like manner (e.g., in rows and columns). Similarly, the component with the vias typically arranges the vias in a complementary manner such that holes of the vias align with ends of the pins when the two components are brought into alignment with one another.
In general, to connect the two components, the housing of the pin-providing component is positioned relative to the via-providing component such that the end of each pin properly aligns with a corresponding via hole. Then, the housing of the pin-providing component and the via-providing component are brought together so that the metal pins evenly insert into the via holes. There are different conventional approaches to making sure that the connections between the pins and the vias are secure.
One conventional approach is called “reflow soldering” or the “wave soldering”. In this approach, wave soldering machinery typically solders the pins and vias together once the pins have been inserted into the vias. In general, molten solder flows through the remaining voids between the pins and the vias to form electrical pathways for carrying signals between the pins and the vias.
Typically, the reflow approach uses a grid pattern pitch of approximately 0.100 of an inch or 0.100″ (often pronounced “100 mils”). That is, the pins are arranged generally in rows and columns such that the center axis of each pin is approximately 0.100″ away from the center axes of pins in adjacent rows and columns. Similarly, the vias typically are arranged in complementary rows and columns such that the center axis of each via is approximately 0.100″ away from the center axes of vias in adjacent rows and columns.
For the reflow soldering approach, the diameters of the holes of the vias typically are 100% larger than the maximum cross-sectional dimension of the pins in order to promote solder flow within the vias once the pins have been inserted. For example, for a round pin having a maximum diameter of 0.030″, the inner diameter of the via hole is generally 0.060″.
In general, pins having a square cross-section, which are stamped from flat metal stock, are also suitable for use in the reflow soldering approach. Such square cross-sectioned shaped pins generally are less expensive than pins having a circular cross-section or pins with rounded corners since the square cross-sectioned pins typically do not need to undergo a tumbling, coining or turning process to round the comers of the pins. Rather, the pin manufacture can simply cut/punch/stamp the square cross-sectioned pins from a sheet of metal stock. Accordingly, the thickness of each pin is essentially the width of the metal stock. Although flat pins are less expensive than rounded pins, better soldering results typically are obtained with pins having circular cross-sections or rounded corners than with pins having a square or rectangular cross-section and sharp comers.
Another approach to forming secure connections is the “intrusive reflow soldering” approach. In this approach, automated equipment typically provides portions of solder and flux for each pin/via combination prior to insertion of the pins into the via holes. Often, the equipment partially inserts these solder portions (sometimes in the form of a paste and sometimes as solder pre-forms assembled to the pin base) into the via holes of a component prior to pin insertion. Then, the equipment brings the pin-providing component and the via-providing component together by inserting the pins of the pin-providing component into the via holes of the via-providing component. The equipment then provides heat to melt the solder portions and additional solder to fill any remaining voids between the pins and the vias.
Typically, the grid pattern for the intrusive reflow approach has a pitch that is similar to that used in the reflow soldering approach (i.e., 0.100″), or a finer pitch in the range of 0.080″ to 0.100″. Furthermore, for the intrusive reflow soldering approach, the diameters of the vias holes typically are not 100% larger than the maximum cross-sectional dimension of the pins, as in the reflow soldering approach. Rather, the via holes for the intrusive reflow approach generally can be 25% larger than the maximum cross-sectional dimension of the pins for sufficient solder distribution since pre-placement of the solder portions facilitates solder delivery into the via holes.
For the intrusive reflow soldering approach, as in the reflow soldering approach, square or round cross-sectioned pins are generally preferred. Pins having a round cross-section are ideally suited for intrusive reflow soldering. Pins having a square cross-section are generally suitable but require more solder. Pins having a rectangular (but non-square) cross-section typically are not used in the reflow soldering approach since such pins provide little or no additional benefit over pins having a square cross-section.
Another approach to forming secure connections between two components is called the “compression fit” approach. This approach is also known as the “compliant fit”or the “eye-of-the-needle” approach. In this approach, no solder is used. Rather, each pin typically is flat (i.e., each pin has a square or rectangular cross-section) and has a hole (or eye) stamped through it (i.e., the “eye-of-the-needle”) allowing the pin to compress when inserted into a via to form a secure connection. In particular, each pin has a cross-sectional diameter that is sized to be larger than the cross-section diameter of its corresponding via hole to provide an interference fit when inserted into that via hole. Accordingly, when the pins are inserted into the holes of the vias, the pins compress to fit within the via holes and apply pressure against the inner metallic surfaces of the vias (e.g., copper-plated surfaces). As a result, the connections formed between the pins and vias are secure.
Typically, the compression fit approach uses a finer grid pattern pitch than either the reflow soldering approach or the intrusive reflow soldering approach. One example of a pitch that is suitable for the compression fit approach is an 0.080″ by 0.060″ grid. Connection systems which used grids of this size are often called “high-density” due to the large number of connections (i.e., pin/via connections) that can be formed in such a small area.
Typically, pins which have a rectangular or even square cross-section are used in the compression fit approach. The range for a typical width for a rectangular pin suitable for use in the compression fit approach is 0.012″ to 0.015″. The range for a typical pin length is 0.026″ to 0.028″. The sides of the compression-fit pin typically are allowed to vary by 0.002″ in either direction. A particular characteristic of compression fit pins is their central portions which have a bulging shape. That is, the shape of the eye and the pin material around the eye is designed to provide a particular form factor, and a particular size reduction when inserted into a via.
SUMMARY OF THE INVENTION
Unfortunately, there are disadvantages to the conventional reflow soldering, compression fit and intrusive reflow soldering approaches. For example, the conventional reflow soldering approach generally is not used in high-density connection applications (e.g., in connection arrangements having rows and columns less than 0.100″ apart) for several reasons. In particular, reflow soldering connection systems are susceptible to tail shorts, i.e., s
Chaplin & Huang, L.L.C.
Cuneo Kamand
Huang, Esq. David E.
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