Electrical connectors – Metallic connector or contact having part permanently... – Adapted to be secured to conductor formed on printed circuit...
Reexamination Certificate
2000-07-10
2001-07-17
Sircus, Brian (Department: 2839)
Electrical connectors
Metallic connector or contact having part permanently...
Adapted to be secured to conductor formed on printed circuit...
C439S083000
Reexamination Certificate
active
06261136
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to terminals adapted to be soldered to contact pads to form electrical connections, particularly terminals with attached solder masses. The terminal is placed in contact with a pad and heated so that the solder melts and flows into the interface between the terminal and the pad to form a soldered connection.
DESCRIPTION OF THE PRIOR ART
In the electronics industry it is conventional to mount highly miniaturized circuits on flat substrates. Electrical connections are established between the circuits and spaced pairs of contact pads extending along one or more edges of the substrate. The pads are closely spaced together in order to provide the number of electrical connections required by the circuit on the substrate. In many applications, it is desirable to attach elongate leads to each pair of opposed contact pads extending along a substrate edge. Clip type terminals may be fitted over pairs of opposed pads and then soldered to the pads.
It is now conventional to manufacture solder clip terminals with individual solder masses secured to solder contacts on opposed sides of the substrate so that after the clip is physically mounted on the substrate the soldering operation is completed by heating the clips and the solder masses to melt the solder and form reflowed solder connections with the pads. Solder clips of this type are disclosed in U.S. Pat. Nos. 4,367,910, 4,679,889 and 5,688,150.
Solder clip terminals are conventionally manufactured by stamping thin strip metal stock. The terminals include leads extending laterally from a carrier strip with clips on the ends of the leads. The leads and terminals are closely spaced along the length of the strip. Solder masses are conventionally joined to the clip terminals by extending a continuous solder wire along the terminals, parallel to the carrier strip, attaching the wire to each terminal and then severing and discarding portions of the solder wire located between adjacent terminals. The remaining sections of solder wire are attached to the terminals by bending or folding a portion of the terminal around the solder wire or by forming the severed portion of the wire around the terminal. In either case, the solder terminal is expensive to manufacture because a large percentage of the solder wire used in making the terminals is cut away and discarded.
In terminals where a portion of the terminal is wrapped around a short length of solder wire to hold the solder wire in place the solder wire does not engage the contact pad. Rather, the contact engages the pad and separates the solder a distance from the pad. In some cases, difficulty is encountered in flowing molten solder from the length of wire across the thickness of the terminal and into the interface between the pad and contact. This problem can cause a poor or failed solder connection between the terminal and the pad.
Further, reflow soldering heats the entire terminal, including the contact and the terminal tail, to a high temperature. When the solder melts the molten solder tends to wick along the heated metal and away from the contact pad, reducing the volume of solder available for establishing the desired electrical connection. This problem can result in weak or malformed soldered connections with the pads. Wicking of molten solder to a portion of the terminal away from the contact undesirably changes the dimensions of the portion and can prevent subsequent use of the portion.
In conventional solder terminals where a solder mass is held on the terminal and directly engages the contact pad when the terminal is mounted on the pad, melting of the solder mass may weaken the physical connection between the contact and the pad and permit undesired relative movement between the solder terminal and the pad.
Thus, there is a need for an improved solder terminal for forming an electrical connection with a substrate contact pad where a mass of solder is secured to the terminal, the terminal is stably mounted on the pad during soldering, both the terminal and the mass of solder engage the contact pad when the terminal is mounted on the pad and when the mounted terminal and pad are heated the solder melts and flows reliably to the connection between the terminal and the pad, without wicking along the terminal away from the pad. The terminal should be inexpensive to manufacture without solder waste.
SUMMARY OF THE INVENTION
The invention is an improved solder terminal for forming reliable soldered electrical connections with substrate contact pads. The terminal includes a solder contact with a pair of contact arms or bridges facing the pad, a pair of base members joined to the ends of the arms and a gap between the base members. One of the base members is attached to a lead extending away from the terminal for forming an electrical connection with another circuit element. A mechanically formed solder mass is extruded into the contact through the gap, fills the space between the arms and extends outwardly beyond the arms. The shape of the solder mass conforms to the shape of the arms.
The contact is soldered to a pad by placing the arms in engagement with the pad and then heating the terminal and the pad. Heating melts the solder, which includes resin as a flux. The molten solder flows onto the pad and around the arms to form a reliable solder connection. During soldering the arms are maintained in contact with the pad and the contact is stable. The opening between the base members prevents molten solder from wicking away from the contact and along the lead to reduce the volume of solder available at the solder connection and alter the shape of the lead.
The solder contacts are preferably used in double sided edge clip terminals and engage opposed pairs of contact pads on the edge of a substrate. Insertion of a clip onto the edge of a substrate stresses the clip slightly to form a physical connection between the clip and the pads. This connection is maintained during soldering, and assures that the terminal is held tightly in place until the reflowed solder cools and solidifies. The spaced arms engage the pads and hold the terminal stably in place without pivoting or wobbling during soldering.
The solder terminal is manufactured by cutting successive slugs of solder from the ends of solder wires and cold flowing the slugs through the gaps or openings between the base members in the two contacts and into the space between and to either side of the arms, without waste of solder. The cost of manufacturing the terminal is reduced.
Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings illustrating the invention, of which there are four sheets and two embodiments.
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Die Tech, Inc.
Hooker, P.C. Thomas
Prasad Chandrika
Sircus Brian
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