Method for adjusting differential thermal expansion between an electrical socket and a circuit board

• US 6,196,871 B1
• Filed: 04/26/1999
• Issued: 03/06/2001
• Est. Priority Date: 02/02/1999
• Status: Expired due to Fees

• Current Assignee: Hon Hai Precision Industry Co., Ltd.
• Original Assignee: Hon Hai Precision Industry Co., Ltd.
• Inventors: Szu, Ming-Lun
• Primary Examiner(s): Nguyen, Khiem
• Assistant Examiner(s): HYEON, HAE M
• Application Number:
  US09/299,334
• Time in Patent Office: 680 Days
• Field of Search: 439/571, 439/525, 439/330, 439/572, 439/573, 439/876
• US Class Current: 439/571
• CPC Class Codes: H01R 43/0256 for soldering or welding connectors to a printed circuit board
• CPC Class Codes: H01R 43/0263 for positioning or holding parts during soldering or welding process
• CPC Class Codes: H05K 2201/0129 Thermoplastic polymer, e.g. auto-adhesive layer; Shaping of thermoplastic polymer
• CPC Class Codes: H05K 2201/068 wherein the coefficient of thermal expansion is important
• CPC Class Codes: H05K 2201/10325 Sockets, i.e. female type connectors comprising metallic connector elements integrated in, or bonded to a common dielectric support
• CPC Class Codes: H05K 2203/167 Using mechanical means for positioning, alignment or registration, e.g. using rod-in-hole alignment
• CPC Class Codes: H05K 3/303 Surface mounted components, e.g. affixing before soldering, aligning means, spacing means H05K3/32 takes precedence
• CPC Class Codes: H05K 3/305 Affixing by adhesive
• CPC Class Codes: H05K 3/3436 having an array of bottom contacts, e.g. pad grid array or ball grid array components
• CPC Class Codes: Y02P 70/50 Manufacturing or production processes characterised by the final manufactured product

Abstract

The present invention relates to a method for adjusting differential thermal expansion between an electrical socket and a circuit board by means of secure and accurate interconnection of an adjusting device therebetween before a heating step. The adjusting device is made of an adhesive fusible material and fixed to the housing for absorbing most of the fracture stress exerted on the solder balls and for eliminating a misalignment between the electrical socket and the circuit board during the heating step. The adjusting device can be designed according to practical requirements to be a number of adjusting posts, an adjusting frame, or an adjusting chip.

Claims

1. A method for mounting a ball-grid-array (BGA) electrical socket to a circuit board, said electrical socket and circuit board having different coefficients of thermal expansion (CTE), said method comprising the steps of:

(a) manufacturing an electrical socket and a circuit board, a plurality of contacts received in the electrical socket, a plurality of contact pads formed on the circuit board corresponding to the contacts of the electrical socket, a plurality of holes defined in the electrical socket surrounding the contacts, and a plurality of positioning holes defined in the circuit board and corresponding to the holes of the electrical socket;

(b) planting a plurality of solder balls onto the corresponding contacts of the electrical socket;

(c) disposing a plurality of posts made of adhesive fusible material into the holes of the electrical socket and the positioning holes of the circuit board; and

(d) subjecting the electrical socket and the circuit board to a heat treatment process to cause the solder balls of the electrical socket to be soldered to the contact pads of the circuit board and the posts to melt and then solidify to fix the electrical socket to the circuit board, said posts absorbing most of fracture stress exerted on the solder balls by the socket and the circuit board due to the different CTEs of the electrical socket and the circuit board thereby preventing misalignment between the contacts of the electrical socket and the contact pads of the circuit board.

2. The method as claimed in claim 1, wherein the posts are made of thermoplastic material.

3. An electrical socket for electrically connecting a modular chip and a circuit board, comprising:

an insulative housing forming a mating face for connecting to the modular chip, a jointing face for connecting to the circuit board, a plurality of engaging slots and holes defined between the mating face and the jointing face, the holes being located around the edges of the housing;

a plurality of matrix type contacts received in the corresponding engaging slots and a plurality of solder balls planted on bottom ends of the contacts, the contacts being adapted to be soldered to the circuit board after undergoing a heating procedure; and

a plurality of adjusting posts made of adhesive fusible material and fixed in the holes of the housing, at least a portion of each adjusting post extending outside of the housing and being adapted to be fixed to the circuit board after undergoing the heating procedure, the adjusting posts circumferentially enclosing the contacts of the electrical socket in a limited space and absorbing most of the fracture stress exerted on the solder balls by the socket and the circuit board when the socket is mounted to the circuit board and subject to a thermal load, thereby preventing misalignment between the contacts of the electrical socket and the circuit board.

4. The socket as claimed in claim 3, wherein the adjusting posts are made of a thermoplastic material.

5. A method for mounting an electrical socket to a circuit board, comprising the following steps:

preparing an adjusting device made of thermoplastic material;

preparing a circuit board having a corresponding plurality of contact pads and a positioning hole;

preparing an electrical socket having a hole and a corresponding plurality of ball-grid-array (BGA) contacts with corresponding solder balls attached thereto, bringing the adjusting device to be received in the hole of the electrical socket, and positioning the socket together with the adjusting device to the circuit board to cause the contacts of the socket to contact the pads, and the adjusting device to engage the positioning hole of the circuit board;

heating the socket together with circuit board to a temperature melting the solder balls and the adjusting device;

solidifying the adjusting device so that it fixedly connects the socket and the circuit board together whereby a large portion of fracture stress which would be exerted on the solder balls during thermal loading due to different coefficients of thermal expansion of the socket and the circuit board is absorbed by the adjusting device.