Work machines such as agricultural tractors, combines, construction and forestry equipment continually rely to a greater extent upon electronics and electronic controls. Work machines may operate in extreme environments compared to other applications. Among other concerns, it is necessary for on-board electronics to be designed from an electronics packaging standpoint with vibration, heat transfer and electro-magnetic interference (EMI) in mind. Thus, electronics for work machines must be generally of a robust design.
A common method of mounting a daughterboard to a motherboard is using a commercially available plastic circuit board guide, such as available from RichCo (see http://www.richco-inc.com). Referring to FIG. 1, these circuit board guides snap through slots in the motherboard and project up from the surface of the motherboard. The daughterboard slides down in grooves formed on the edges of the circuit board guides. Small wings near the base of the guide, seen more clearly in FIG. 2, extend out and make contact with the motherboard to provide some stability (limits side-to-side movement). Flaps on the bottom of the base act like a harpoon head, first pushing through the mother board and then snapping out to prevent inadvertent removal.
Another type of commercially available circuit board guide referred to as a vertical mount card guide is more rigid in that is made of metal and mounts by screwing tightly into the motherboard. A number of screws pass through holes in the motherboard and screw into the base of the vertical mount card guide.
Commercially available circuit board guides as described above include certain inherent problems. For example, with a circuit board guide as described above, there is a certain amount of “float” of the circuit board in the tracks of the guide. This float can be back and forth in the track or up and down (away from and toward the motherboard).
Moreover, known circuit board guides do not guarantee a high degree of perpendicularity between the daughterboard and motherboard. Although a vertical mount card guide may do a better job of guaranteeing perpendicularity by requiring screws to mount the guides to the motherboard, the screws add cost to the unit, both in material cost for the screws, and in labor to attach the screws to the board. Further, circuit board guides available off-the-shelf today are designed for taller circuit boards and computer cards. The typical application of these guides is to fit various circuit boards into a predefined volume of space, such as the casing for a personal computer, and perpendicularity is not necessarily required. Few if any are available for a short profile board which must be rigidly perpendicular to the motherboard.
The electrical connection at the interface between the daughterboard and motherboard can be of various known types, such as with a plug-in edge connector, soldered pins, soldered pads, etc. For example, to complete the electrical connection between the daughterboard and motherboard, solder may be applied between metal pads on one board and similar pads on the second board. The end of the daughterboard is placed such that the pads carried thereby are in close proximity to the pads on the motherboard. Solder “bridging” is when solder flows between two adjacent pads and causes an electrical short circuit. It is not easy to control the placement of solder to form the joint between the two boards. Because the placement of solder is difficult, and because the daughterboard is placed at a 90-degree angle to the motherboard (minimizing surface contact), the solder joints can be weak. If the circuit card guides allow even a small amount of side to side movement, the solder joint can break (causing an open circuit or intermittent contact).
What is needed in the art is a circuit board arrangement in which perpendicularity and electrical contact between the daughterboard and motherboard is ensured, and relative movement between the daughterboard and motherboard is minimized.