Design Feature: June 22, 1995

One of the first places where OEMs requiring PCMCIA functions can look for cost reductions is in the area of connector components and their associated manufacturing costs. Unfortunately, the rousing success of the PCMCIA standard has all but eliminated the ability to reduce costs of the connector component itself. Limited capacity of the few quality suppliers and the scanty availability of one-to-one second sources are preventing price reductions.

Although capacity and second sourcing will improve, the current pricing structure is unfortunately at a point of minimum flexibility. Given this pricing scenario, the only viable cost-reduction avenue open to OEMs is in manufacturing.

One of the principal ways to secure any connector product to a pc board is to use nuts and bolts, which prov ide mounting stability against board movement during soldering. They also provide a strain relief against the stress that arises in normal use. Unfortunately, because of the small hardware size and multiple hold-down locations needed for PCMCIA applications, the installation of nuts and bolts is arduous at best. Eject-type sockets require four hold-downs, and non-eject sockets typically require two.

Fig 1 shows the typical placement and hardware needed to secure sockets to the pc board. To install the necessary M2-type nuts and bolts, you must manually insert the bolt from the bottom of the board, while simultaneously providing some method to manually align the corresponding nut in the top slot of the socket. This balancing act becomes somewhat easier if you first prepare the nut with some kind of adhesive to help in securing the optimum alignment position for the corresponding bolt. What's painfully obvious is that in applications needing moderate- to high-quantity component placement, and in which automatic pick-and-place is necessary, the manual procedure all but eliminates any cost advantage the use of nuts and bolts could provide.

Scrapping the nuts and bolts

In the effort to facilitate automatic pick-and-place of these sockets and thereby reduce costs, several objectives are necessary to provide a viable alternative to the hand-placement procedures. First, the alternative process must be suitable for all varieties of pick-and-place equipment, from the current Fuji lines to Dynapert equipment. Because of the large variations in parameters (such as placement tolerances and pushdown forces) of these pick-and-place machines, the need exists for an inherent solder-retent clip that you can install with zero insertion force (ZIF).

This ZIF solder-retent clip (Fig 2) must be inherent in the sense that it must be an integral, preinstalled option on the PCMCIA socket. Preinstallation eliminates the need for costly hand insertion into the socket, and also eliminates the need to order and stock an additional part. To facilitate pick-and-place procedures, the solder-retent clip must also provide alignment to the pc board via its mounting through holes. Therefore, the solder-retent clip must extend beyond the insulator or body of the socket to provide this necessary alignment.

As you can see inFig 2, the solder-retent clip is a true ZIF part, with the latching member entirely encapsulated by the high-temperature plastic body. The socket manufacturer then installs the body into the existing hold-down holes of the socket insulator, as shown inFig 3. Note that the solder-retent clip extends beyond the flush body of the PCMCIA socket by 0.110 in. (on average) to provide alignment. The design and manufacturing departments at most users' facilities require the solder-retent clip to fit into existing through holes currently used for hold-down hardware on the pc boards. To accommodate this need, the solder-retent pin is designed to fit into the same 0.086-in. hole a typical M2 bolt would require.

The final aspect of the solder-retent clip to consider is the retent member itself. Based on current user applications, the retent clip must accommodate pc-board thicknesses ranging from 0.040 to 0.093 in. An additional requirement is that the clip provide a minimum hold-down force of 5 lbs, a figure deemed necessary to keep the socket stabilized during the soldering process. The solder clip must also be easy to activate without the use of special tools or hardware.

Because many applications require the use of an ESD-clip system (which typically carries the ground path through the mounting hardware) in the socket, the retent clip should be conductive and should make contact with the ESD clips. Finally, the retent clip should be able to adequately wick solder so that, once soldered, the clip provides a hold-down strength of at least 10 lbs. This 10-lb force is adequate to provide the necessary retention of the socket on the pc board, in order to resist any forces in the x- or y-axis during insertion and extraction of PC Cards, either into an eject or non-eject socket.

Fig 4 provides an overview of how the retent-clip system meets the cited requirements. As shown, you activate the metallic retent clip by pushing down on its head with a simple screwdriver or any other flat-tip device. This downward motion causes the inherent plastic beam of the solder-retent-clip body to spread the two independent "legs" of the solder clip. This simultaneous downward and outward motion of the retent clip's legs provides the necessary retention forces needed to stabilize the socket during the reflow process. Because the retent clip is made of stamped metal, it provides you with a solderable clip that is also conductive.

As you can see in Fig 5, the head of the activated retent clip rests squarely on the extension of the socket's ESD clip, and, thus, provides the needed ground path. The user's cost averages about $0.04 per solder-retent clip, or $0.16 total for an eject socket. If you compare this cost with current manufacturing direct-labor costs, the savings are at least $0.50 per socket. This conservative calculation assumes an average manufacturing labor cost of $14 per hour, or $0.23 per minute. The calculation uses an optimistic rate of 2.87 minutes to install four M2 nuts and bolts.

As the need for keeping costs down extends to all areas of consumer-electronics design and manufacturing, savings such as those achieved by using solder-retent clips become significant. In a marketplace where every cent counts, such cost savings become particularly crucial if your competitor enjoys them and you don't.

Bill Kuypers is product-marketing manager at Robinson Nugent Inc in New Albany, IN, where he's worked for two years. He obtained BS, BA, and MBA degrees from the University of Florida, Gainesville, FL. He qualified as a CPA at Florida Atlantic University, Boca Raton, FL. Kuypers is a member of PCMCIA.