Electrical connectors – Heat responsive contact pressure control
Reexamination Certificate
2002-05-20
2004-07-20
Duverne, J. F. (Department: 2839)
Electrical connectors
Heat responsive contact pressure control
C361S773000
Reexamination Certificate
active
06764325
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to an apparatus and method for securing components to carrier substrates. In particular, the present invention relates to a zero insertion force heat-activated retention pin that ensures a good electrical connection between the component and the carrier substrate, and minimizes the potential for open electronic connections.
BACKGROUND OF INVENTION
Decreasing packaged circuit board size, decreasing packaging costs, and increasing component packaging density are ongoing goals of the computer industry, and specifically the substrate packaging industry. Accordingly, various components are typically connected to the carrier substrate, for example printed circuit boards, through an electronic connection made by a conductive material, such as solder. Some components connect directly to the carrier substrate, such as capacitors, resistors, CPUs and the like. Other components detachably connect to the carrier substrate through various connectors, which are connected to the carrier substrate. Connectors come in a variety of sizes and mount to carrier substrates to enable various memory modules and input output devices to electrically connect to the carrier substrate. Example connectors include Dual In-line Memory Module Sockets (“DIMM Sockets”) and card edge connectors for secondary boards.
The effectiveness of the components that connect to the carrier substrate depends largely on the integrity of the electrical connection between the carrier substrate and the particular connector or component. Two primary techniques to attach components to carrier substrates are Through hole mount technology (“THM”), and surface mount technology (“SMT”).
THM has been the standard way of attaching components, especially connectors, to carrier substrates for over forty years. In THM components, the component leads consist of individual pins that engage a corresponding electrical interface pattern, which are holes in the carrier substrate (see
FIG. 6A
for an example of a THM connector) that form a hole pattern. THM technology, however, limits the density that components can be placed on a carrier substrate because the holes penetrate all layers of the carrier substrate, which in turn restricts or blocks routing channels on every layer.
SMT is a newer technology, but has been used for over fifteen years. SMT differs from THM in that the electrical interface pattern on the carrier substrate are not holes, but rather consists of pads that reside on the surface of the carrier substrate. The component, then, sits on top of the carrier substrate with its component leads in contact with or close proximity to the carrier substrate electrical interface pattern. This maximizes the available routing space on the carrier substrate and allows denser packing of components.
Currently, both THM and SMT components are typically fixed to the board through a soldering process. THM components typically go through a wave soldering process, which is well known to those skilled in the art. Briefly, in a wave soldering process, THM components are placed on the carrier substrate, the carrier substrate enters the wave solder machine, encounters a preheat region, and is passed over the top of a molten solder wave. When the solder wave contacts the portion of the component leads protruding through the electrical interface pattern holes, the solder is drawn up into the hole and the component lead via capillary action. As the board moves beyond the solder wave, the temperature is reduced and the solder solidifies, securing the connection between the component lead and the electrical interface pattern hole in the carrier substrate.
SMT components are typically connected to the carrier substrate through a solder reflow process. The solder reflow process is also well known in the art of carrier substrate packaging. A conductive material is placed on the carrier substrate at designated spots to which the leads of the component are to attach. The component is placed onto the carrier substrate with conductive material (e.g. solder) residing between the component leads and the electrical interface pattern of the carrier substrate. The carrier substrate then passes through a reflow oven where it encounters a profile of gradually rising temperature, reaching a peak temperature above the solder reflow temperature where the conductive material melts and makes the electrical connection. The process is concluded with a cool down period where the conductive material solidifies. The solder reflow process is more desirable than the wave solder process in that it is generally more efficient, environmentally friendly, and cost effective.
A problem exists, however, with both the wave solder process and the solder reflow process. As the board passes through the higher temperatures, the carrier substrate tends to sag. When dealing with longer components, for example card edge connectors and DIMM sockets, the sag of the substrate creates a space between the connector and substrate, resulting in potentially open connections (see FIG.
7
A).
In order to prevent carrier substrate sag in both the solder reflow and the wave soldering processes, state of the art components include retention pins that forcibly engage holes in the carrier substrate. These retention pins come in a variety of shapes and designs, including barbed or tapered as shown in
FIGS. 7B and 7C
, respectively. The state of the art retention pins require a certain amount of insertion force to cause the retention pin to snap (barbed tip) or wedge (tapered tip) into the carrier substrate hole such that it retains the carrier substrate in a coplanar relationship with the connector and prevents sag as the carrier substrate passes through a soldering process.
Though the state of the art retention pins may help prevent sag, they present other problems in the carrier substrate packaging process including the occupational safety concern of repetitive motion injuries for human placed components, most SMT placement machines are not designed to apply the necessary force to a component as it is placed on the board, and forcibly inserting components onto a carrier substrate increases the risk of damaging component leads.
It would thus be advantageous to develop a retention pin that can be used with either THM or SMT components that would require no force to insert the retention pin and yet would prevent board sag while the board passes through an increasing temperature profile, as encountered, for example, in the solder reflow or wave solder processes.
These and other variations as well as the invention itself will become more readily apparent upon reference to the following detailed description.
REFERENCES:
patent: 4487465 (1984-12-01), Cherian
patent: 4505532 (1985-03-01), Hine et al.
patent: 6617522 (2003-09-01), Tabacutu
Arrigotti George
Aspandiar Raiyomand
Combs Christopher D.
Pearson Tom E.
Duverne J. F.
Intel Corporation
Schwabe Williamson & Wyatt P.C.
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