Patent Application
20100122458
This application is directed, in general, to a connector pin for a printed wiring board and, more specifically, to a printed wiring board connector pin that has an acircular profile.
Many current electronic product assemblies are manufactured from components or sub-assemblies provided to a manufacturer by a vendor/subcontractor. A common method of assembly of such products is to connect leads/terminals of the components or subsystem printed wiring assemblies (PWAs) onto the main system PWB by mass soldering. The two most common continuous mass soldering processes are wave soldering and reflow soldering. Wave soldering is commonly used when a high mix of through-hole components are involved in the product assemblies. Often, in such applications, the sub-assembly is connected to the main system PWB by one or more connector pins that are lathed from a cylindrical, material stock of conductive material, such as copper or aluminum. A segment of the connector pin is lathed from the cylindrical stock material to include a set-off or spacing segment. The spacer segment is lathed to have a diameter larger than the connecting via that goes through the PWB.
The spacer segment is typically seated against the surface of the main system and covers the connecting via. Due to this configuration, it is often difficult to get a lead-free solder to flow into the space between the wall of the via and the connector pin. This can result in a poor or inoperative connection. This flow problem has arisen recently due to the shift in the industry from lead based solders, which have a greater affinity of wetting the PWB than lead-free solders.
One aspect of this disclosure provides an electrical connector pin for a printed wiring board. This embodiment includes an unmachined, collar having an acircular configuration and including a side wall and first and second opposing planar faces perpendicular to a longitudinal axis of the collar. This embodiment further includes a machined first cylindrical connector shaft integrally formed with the collar and extending from the collar along the longitudinal axis, and a machined second cylindrical connector shaft integrally formed with the collar and extending from the collar and along the longitudinal axis in a direction opposite to that of the first cylindrical connector shaft.
Another aspect provides an electrical printed wiring board assembly. This embodiment comprises a first printed wiring board (PWB) having a via located therethrough and an electrical connector pin extending through the PWB. In one embodiment, the electrical connector pin comprises a collar having a sidewall that defines a perimeter of the collar. The sidewall has a bar stock profile that has a cross-section dimension perpendicular to a longitudinal axis of the bar stock that is less than a diameter of the via that forms a vent space between the via and a portion of the cross-section dimension. The connector pin further includes a machined first cylindrical connector shaft extending from the collar along the longitudinal axis. At least a portion of the connector shaft is received within the via and electrically connected to the PWB by a conductive material located within the via. The pin further includes a machined second cylindrical connector shaft extending from the collar along the longitudinal axis in a direction opposite to that of the first cylindrical connector shaft.
Another embodiment provides a method of fabricating an electrical assembly. This embodiment comprises providing a bar stock of a conductive material, wherein the bar stock has an acircular profile. Portions of the bar stock are removed to leave a collar having a sidewall that defines a perimeter of the collar and an acircular profile. The removal step forms a machined first cylindrical connector shaft integrally formed with the collar and extending from the collar along the longitudinal axis and a machined second cylindrical connector shaft integrally formed with the collar and extending from the collar along the longitudinal axis in a direction opposite to the first cylindrical connector shaft. The method further includes placing the first cylindrical connector shaft into a via of a first printed wiring board (PWB), such that at least a portion of the first cylindrical connector shaft is located within the via and electrically coupling the first cylindrical connector shaft to the PWB.
Reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
As discussed below, the collar 120 has an acircular cross-sectional profile such that a portion of the perimeter of the collar 120 is less than a diameter of a via in which the connector pin 110 is inserted. The acircular profile provides a vent through which air may escape, which allows solder to more readily flow between the connector pin and the via. Since the acircular profile can be achieved without the need of machining, the cost and time of manufacture is advantageously reduced.
The acircular profile is original to the material stock or bar stock that is provided (e.g. either obtained from an internal supplier or from an outside supplier) and from which the connector pin 110 is made. As such, the collar 120 is not machined, or “unmachined,” during the formation of the connector pin 110. That is, the original or bar stock material that makes up the collar 120 is not cut or substantially removed such that the original surface profile of the collar 120 is left substantially unchanged or unaltered. For example, drilling a hole in the collar 120 or merely marring the surface does not substantially change the original surface profile. Moreover, the collar is considered not to be machined in those instances where the collar is merely buffed, polished, otherwise smoothed, or is left substantially unchanged.
This is in contrast to conventional connector pins that are typically formed from a circular stock, which results in a circular collar. In such instances, the manufacturers must perform additional machining steps by removing a portion of or beveling an edge of the collar such that a vent is formed between the via of the PWB and the collar. These additional manufacturing steps add cost and time to the manufacturing, which are undesirable.
As seen in this embodiment, the collar 120 includes a sidewall 245 and first and second faces 250, 255, in which the second face 255 contacts the surface of the PWB 220. For purposes discussed herein, the second face 255 is considered to contact the surface of the PWB 220 even though it does not contact the surface of the PWB 220 directly, for example, a thin layer of solder (not shown) may be located between these two structures.
The presence of the vents or spaces 260 are important because industry standards prefer to not use lead based solder for environmental concerns and have turned to the use of lead-free solders that have a high percentage of tin. Lead based solders had the capacity to wet the inside of the via more readily than lead-free solders. Thus, when lead based solders were used, the solder was still able to move up into the space between the via and the connector pin. However, since lead-free solders do no wet as easily, the vent is necessary to allow the air to escape and thereby allow the lead-free solder to move into the space between the via and connector pin more readily.
In embodiment 310, the collar 120 may have a square-shaped cross-section or configuration. The via 230 in the assembly PWB 200 is shown in a dashed line. As seen in this embodiment, portions of the perimeter of the sidewall of the collar 120 do not over lap the via 230. Thus, the vents 260, as discussed above are formed.
In embodiment 315, the collar 120 may have a triangular-shaped cross-section or configuration. It should be noted that the acircular configurations disclosed herein may also include those embodiments where the sidewalls of the collar 120 may be curved. For example, embodiment 315 may also include a Reuleaux triangle shaped cross-section. The via 230 in the assembly PWB 200 is shown in a dashed line. As seen in this embodiment, portions of the perimeter of the sidewall of the collar 120 do not over lap the via 230. Thus, the vents 260, as discussed above are formed.
In embodiment 320, the collar 120 may have a cross-shaped cross-section or configuration. The via 230 in the assembly PWB 200 is shown in a dashed line. As seen in this embodiment, portions of the perimeter of the sidewall of the collar 120 do not over lap the via 230. Thus, the vents 260, as discussed above are formed. The foregoing examples illustrate different polygon shapes that may be used to construct the connector pin 110.
In another embodiment 325, the collar 120 may have an elliptical or oval-shape cross-section or configuration. The via 230 in the assembly PWB 200 is shown in a dashed line. As seen in this embodiment, portion of the perimeter of the sidewall of the collar do not overlap the via 230. Thus, the vents 260, as discussed above are formed.
As mentioned above, it is important to note that, unlike conventional pins, no additional machining is required to form the collars of these various embodiments, since the virgin or original profile of the bar stock material can be used to form the vent. Further, it should be understood that the foregoing are given as examples only and that many other acircular shapes are within the scope of this disclosure.
It has been found that significant manufacturing costs and time can be saved in manufacturing the connector pins covered by this disclosure. For example, it has been unexpectedly found that the effort to produce the pin is reduced by about 20% when using the principles discussed herein. The savings achieved by this 20% reduction are substantial and particularly advantageous when large numbers of pins must be produced. Moreover, choosing an acircular profile is counter-intuitive to standard manufacturing procedures because it is typically desirable to begin with a circular bar stock since the connector pin is to have circular connector shafts. Thus, those who are skilled in the art would not seek to use a bar stock with an acircular configuration absent the teachings of this disclosure.
Those skilled in the art to which this application relates will appreciate that other and further additions, deletions, substitutions and modifications may be made to the described embodiments.
