This invention relates to surface mount connectors, processes for preparing surface mounted connectors, and subassemblies for preparing surface mounted connectors. More particularly, the invention pertains to processes and subassemblies that facilitate a reliable and durable attachment of a connector body to the surface of a circuit board.
The commercial use of surface mount connectors for electrically connecting an electrical device to a circuit substrate has been avoided due to unacceptable reliability. In particular, surface mount connectors used for automotive electronics have exhibited unacceptably high failure rates, which are primarily due to breakage of solder connections between the circuit board and the connector.
The reliability of the solder connections between a circuit board and a surface mount connector can be greatly improved by bonding the connector body to the circuit board. However, bonding of the connector body to the circuit board requires additional manufacturing process steps such as underfilling and/or overmolding.
It would be desirable to achieve the improved reliability associated with underfilling and/or overmolding without the additional manufacturing steps required for underfilling and/or overmolding.
The invention achieves an objective of reliably and durably mounting a connector body to a surface of a circuit board without utilizing conventional underfilling and/or overmolding steps.
In accordance with an aspect of the invention, a process for securing a connector body to a circuit board utilizing a preformed solid mass of adhesive material is provided. The process includes steps of providing the preformed solid mass of adhesive material with a predefined pattern of openings corresponding with a pattern of solder balls on a mounting surface of the connector body. The preformed solid mass of adhesive material is positioned on the mounting surface of the connector body with the openings aligned with the solder balls so that the solder balls project into the openings. The resulting subassembly is positioned on the circuit board with the solder balls aligned with a pattern of contact pads on the circuit board, and with the preformed solid mass of adhesive material disposed between the circuit board and the mounting surface of the connector body. Thereafter, the preformed solid mass of adhesive material is activated to cause it to securely adhere the connector pin carrier to the circuit board.
In accordance with another aspect of the invention, a process for securing a connector body to a circuit board using a liquid adhesive material is provided. The liquid adhesive material is applied to the mounting surface of the connector body, with the liquid adhesive being applied in a pattern that surrounds solder balls on the mounting surface of the connector body. The liquid adhesive is then partially cured to form a subassembly in which the liquid adhesive is converted to a solid adhesive material. The subassembly is positioned on a circuit board with the solder balls aligned with a pattern of contact pads on the circuit board, and with the solid adhesive material disposed between the circuit board and the mounting surface of the connector body. Thereafter, the adhesive is activated to cause it to securely adhere the connector body to the circuit board.
In accordance with another aspect of the invention, a self-adhering connector subassembly is provided. The self-adhering connector subassembly includes a connector body having a mounting surface and a pattern of solder balls on the mounting surface, and an activatable solid adhesive disposed on the mounting surface of the connector body, with the activatable solid adhesive having a pattern of openings into which the solder balls project from the mounting surface.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
This invention provides a process and subassembly 30 for securely attaching a connector body 12 to the surface of a circuit board. The processes of this invention involve preparation of a self-adhering connector subassembly comprising a connector body having a mounting surface, and a solid adhesive disposed on the mounting surface, positioning of the subassembly on the surface of a circuit board, and activation of the solid adhesive to securely attach the connector body to the circuit board.
The connector body may comprise a pin carrier 12 holding a plurality of pins 16, as shown in
The circuit board can be generally any suitable substrate on which electrically conductive pathways or traces can be defined and on which electrical components may be mounted and electrically connected to the conductive pathways or traces to define electrical circuitry. However, the invention is particularly beneficial for use with circuit boards defined on a ceramic substrate, such as a low temperature cofired ceramic (LTCC) substrate, wherein there is a larger difference or mismatch between the coefficient of thermal expansion of the substrate and the connector body.
The expressions “solid mass of adhesive material” and “solid adhesive material” as used to describe and claim the adhesive material disposed on the self-adhering connector assemblies of this invention refers to a material that will not run or flow from the mounting surface of the connector body under the influence of gravity at normal ambient conditions or due to ordinary handling. It does not mean that the adhesive material is necessarily completely devoid of liquid, or that it cannot be caused to liquefy or melt under conditions different from normal ambient conditions. To the contrary, in accordance with certain embodiments of this invention, the solid adhesive is a thermoplastic polymer material that is heated to at least its softening temperature and/or melting temperature to wet the surface of the circuit board, and subsequently cooled to resolidify the adhesive material and form a reliable and durable bond between the connector body and the circuit board.
The term “solder ball” as used herein encompasses solder bumps, solder columns, and the like which are used for mechanically and electrically connecting a surface mount device to a substrate, and is not limited to spherically-shaped solder masses.
The step of activating the activatable solid adhesive disposed on the mounting surface of the connector body refers to a step in which properties of the solid adhesive are modified to induce tackiness of the adhesive material and/or promote wetting of the circuit board and/or subsequent adhesion with the circuit board. In the case of hot-melt adhesives, activation generally refers to melting and/or softening of the adhesive material to form a pliable or deformable mass of material after it is brought into contact with the circuit board, followed by cooling and resolidification of the adhesive to bond the connector body to the circuit board. In the case of thermosettable adhesive compositions, activation may refer to heating or any other activation step which induces chemical cross-linking of polymers or prepolymers in the adhesive composition.
Shown in
As shown in
Adhesive 24 may be preformed and provided with a plurality of openings 26 arranged in a pattern corresponding with the solder ball pattern on connector body 12. Preferably, openings 26 have a diameter that is greater than the diameter of solder balls 18.
As an alternative, adhesive 24 may be applied as a liquid, such as by utilizing an ink jet printing technique, to define an adhesive layer 24 having openings 26.
Suitable hot-melt adhesive compositions that may be employed, and that can be activated (e.g., softened or melted) to develop tackiness and/or bond to a surface, and subsequently solidify to reliably and durably attach connector body 12 to circuit board 14 include polyolefins, polyamides, ethylene-propylene copolymers, styrene-butadiene copolymers, ethylene-propene copolymers, ethylene-vinyl acetate copolymers, and the like.
Suitable thermosettable adhesive compositions include epoxy resins, phenolic resins, and polyimides. Preferred thermosettable resin compositions include partially cross-linked polymer compositions (e.g., so-called B-stage resins).
The thermosettable resins are typically heat activatable, although it is conceivable that other activating techniques may be employed, such as activation by electromagnetic radiation.
In order to improve heat dissipation, it may be desirable to utilize an adhesive material which comprises a thermally conductive particle filler such as carbon black, alumina or zinc oxide, in an amount sufficient to provide a thermal conductivity in the range from about 0.5 to about 1.0 w/M−K.
While it is conceivable that activation of the adhesive and solder reflow may be achieved in separate steps, it is preferable that solder reflow and activation of the adhesive material occurs concurrently upon application of heat to the device 10 after subassembly 30 has been properly positioned on the circuit board with solder balls 18 properly aligned with contact pads 20. Such heating can be achieved in an oven or by use of infrared radiation.
The invention provides a product that exhibits decreased sensitivity to handling damage, lower transmitted forces to the solder joints during connector engagement and disengagement, and lower stresses during temperature excursions. These advantages provide increased component solder joint reliability and durability. Application of the adhesive to the connector body prior to mounting the connector body on the circuit board results in savings in the production process, such as by eliminating underfill manufacturing processes. Because the adhesive joint may be formed during the solder reflow process, additional curing process steps may be eliminated.
It will be understood by those who practice the invention and those skilled in the art that various modifications and improvements may be made to the invention without departing from the spirit of the disclosed concept. The scope of protection afforded is to be determined by the claims and by the breadth of interpretation allowed by law.