Method of reforming reformable members of an electronic package and the resultant electronic package

#The invention relates generally to electronic packages and more particularly to assemblies for connection of integrated circuit chips to chip carriers, chip carriers to printed circuit boards, modules to printed circuit cards, and the like.

#Various ceramic ball grid array packages, leadless chip carriers, laminated chip carriers, tape ball grid array packages, and overmolded, globtop, and plastic ball grid array packages are known today. Such packages typically contain a semiconductor device (a chip) and provide for electrical and thermal connection paths to and from the chip, while protecting the chip from extraneous environmental factors, processing chemicals, and handling.

#Such packages typically include connections known in the art as solder reflow (or melt) connections. These connections provide for both electrical and thermal conduction paths. It is known from prior art that a reformable solder ball 107 can be attached to contact pad 105 on substrate 103 of electronic package 101, as depicted in FIG. 1. Further, as depicted in FIG. 2, it is known from prior art that solder ball 207 can be attached to contact pad 206 of substrate 204. Typically substrate 204 is circuitized. Solder ball 207 provides a standoff distances between contact pads 205 and 206; this standoff provides mechanical compliance between the two substrates. It is also known that a higher standoff, with resulting increased compliance, can result in improved resistance to fatigue. The connections may be formed between a chip and a circuitized substrate, serving as a chip carrier package. Examples of circuitized substrates include printed wiring boards, flexible circuit cards, laminated chip carriers, metallized ceramic substrates, and multi-layer ceramic substrates. When a chip is connected to a circuitized substrate with numerous solder reflow connections, this form of connection is also known in the art as “flip-chip” or controlled collapse chip connection (C4), and results in a flip chip package.

#FIG. 1 is a partial side sectional view, in elevation and on a much enlarged scale, of an electronic package in accordance with prior art.

#FIG. 2 is a partial side sectional view, in elevation and on a much enlarged scale, of the electronic package of FIG. 1 connected to a circuitized substrate in accordance with the prior art.

#FIG. 3 is a partial side sectional view, in elevation and on a much enlarged scale, of an electronic package with a reformable solder ball positioned to receive an elastic sleeve in accordance with the present invention.

#Referring now to the drawings in detail, FIGS. 3-5 illustrate a process for making an electronic package according to one embodiment of the present invention. The electronic package 301 comprises a substrate 303, a contact pad 305, and a reformable ball 307. By way of example, reformable ball 307 is a solder ball. An elastic sleeve 309 is formed from rubber, plastic or a shaped memory alloy and is initially apart from electronic package 301. When relaxed, an inner diameter (shown in phantom) of elastic sleeve 309 is less than an outer diameter of reformable solder ball 307. In FIG. 4, elastic sleeve 309 has been positioned around reformable solder ball 307 by stretching the elastic sleeve from its relaxed state to an unrelaxed state conforming to the outside diameter of the reformable solder ball 307. To ease application of the elastic sleeve, a lubricant such as a solder flux may be employed. A girdling (or squeezing) pressure now exists between elastic sleeve 309 and reformable solder ball 307, while ball 307 is in a solid condition. By heating reformable solder ball 307 to its softening temperature, the solder ball responds to the girdling pressure exerted by elastic sleeve 309. Consequently, reformable solder ball 307 takes a new elongated shape depicted in FIG. 5 as reformed, nipple-shaped solder 507, which shape is predetermined and held by now-relieved elastic sleeve 309. After reshaping, the stiffness of the reformed solder 507 may be increased by reducing temperature. In particular, an increased standoff distance h' between contact pad 305 and the tip of reformed solder 507 is evident (as compared to distance h in FIG. 3).

#The method for making and utilizing an elongated reformed slug may be varied somewhat depending on the materials chosen, so several examples will be given to illustrate how to best implement the present invention.

#Softening of many materials such as plastics, epoxies, metals, and organic materials is known to occur at increased temperature. With some materials, such as solder, a phase change from solid to a melt or molten state of the material can be achieved at a sufficient temperature. The molten state exhibits essentially a zero shear modulus. Eutectic tin-lead solder, for example, has a melting phase transition point of about 183° C. (Centigrade). Higher melting point solders can be obtained with various ratios of tin and lead: about 3% tin and about 97% lead is a common high-melt (about 310° C.) alloy.