Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
1998-12-10
2001-02-13
Pyon, Harold (Department: 1722)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S347000, C228S254000, C228S033000
Reexamination Certificate
active
06186216
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to connectors for electrical and microelectronic devices and, in particular, to an apparatus and method for extracting a cast column grid array and bonded substrate from the column grid array mold.
2. Description of Related Art
Cast column grid array (CCGA) connections are used in place of conventional solder balls to electrically connect microprocessors and other electronic components to supporting substrates. With the need for increasing cast column grid array densities, such as recent products having a pitch or column-to column spacing of one millimeter, the process of extracting the CGA substrates from the graphite casting mold becomes more difficult. Present methods for extracting the CCGA substrates from casting molds are labor-intensive, and subject the mold and CCGA product to damage.
Prior art methods specifically directed at CCGA extraction have been tried with only limited success. Using a clamp to pull or unplug the assembly often results in tensile failure of the soft cast pins, as well as imposing a requirement for relief features on the carrier side of the mold that weakens it. The employment of interstitial or edge bearing pins that bear on the carrier have also been tried with limited success due to the lack of clearance between pins and/or part damage from limited bearing surface. Implementation of close tolerance injection molding also eliminates the option of providing clearance holes for extraction within the area of the feature array, since all features in this area will be filled with solder or other casting material. If the extraction forces do not lift the array out in a perpendicular fashion, the cast pins tend to bind in the mold bores. The resulting jamming causes pin and mold damage as well as terminally jamming the cast array in the mold.
Extraction of molded structures by use of multiple ejector pins typically utilize a set of pins integral to the mold structure itself and do not address electronic assemblies. Prior patents such as U.S. Pat. No. 5,429,492 to Taniyama, U.S. Pat. No. 5,236,364 to Herbst, U.S. Pat. No. 4,009,979 to Martin, U.S. Pat. No. 3,899,282 to Jesse, and U.S. Pat. No. 4,661,055 to Prince disclose a variety of pin-type extraction schemes that do not address extraction of remotely filled molds/castings that have been subject to a secondary casting/attachment step.
Accordingly, there is a need for a process and apparatus which overcomes the aforementioned problems and extracts CCGA substrates from the casting mold with very little operator effort, and may further be utilized with automated tooling.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide an improved process and apparatus for extracting from a casting mold.
It is another object of the present invention to provide a CCGA substrate extraction process and apparatus which is less labor-intensive.
A further object of the invention is to provide an extraction process and apparatus which is less susceptible to damaging the CCGA substrate and/or interconnect on the array.
It is yet another object of the present invention to provide a CCGA substrate extraction process and apparatus which may accommodate various grid arrays and can be automated.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
SUMMARY OF THE INVENTION
The above and other objects and advantages, which will be apparent to one of skill in the art, are achieved in the present invention which is directed to, in a first aspect, an apparatus for removing a casting comprising an electronic package or other type substrate and an array of columns, such as a bonded cast column grid array, extending therefrom from the corresponding openings of a mold. The apparatus includes a frame and a compression plate secured to the frame. The compression plate includes an opening therein for receiving the substrate without interference. The apparatus also includes a graphite or other type mold containing a plurality of openings, preferably more than 2, for casting a corresponding array of columns and bonding the columns to the underside of a substrate when the substrate is disposed on the mold and a stripper plate on the frame for receiving the mold. The stripper plate contains openings therein corresponding to at least some of the openings in the mold. The apparatus further includes an ejector assembly on the frame including a plurality of ejector pins extending therefrom, with at least some of the ejector pins corresponding to openings in the mold and the stripper plate. At least one of the compression plate and the ejector assembly is movable on the frame toward the other to cause at least some of the ejector pins to engage cast columns in the mold openings and push the engaged cast columns and substrate out of the mold.
Preferably, the ejector pins have a length at least as long as the sum of the thickness of the stripper plate at the stripper plate openings and the thickness of the mold at the column casting openings, although the ejector pins may have a length less than the sum of the thickness of the stripper plate at the stripper plate openings and the thickness of the mold at the column casting openings. Preferably, the compression plate opening is larger than the substrate. The apparatus may further include pins for aligning the mold to the stripper plate, with the mold being removable from the stripper plate.
The stripper plate is adapted to be movable relative to the ejector pins away from the ejector assembly after the ejector pins push the cast columns and substrate out of the mold, and preferably the apparatus further includes means for separating the stripper plate and the ejector assembly.
The number of ejector pins in the ejector assembly may be less than, equal to, or greater than the openings in the mold for the cast columns and wherein at least one ejector pin is not able to engage a cast column in the mold openings. The apparatus may further include one or more recesses in the ejector assembly corresponding to the at least one ejector pin not able to engage a cast column in the mold openings to enable the at least one ejector pin to avoid engagement with the mold as the compression plate and the ejector assembly move relatively toward the other. The ejector pins may have heads for bearing against the ejector assembly as at least some of the ejector pins engage cast columns in the mold openings, and the recesses in the ejector assembly may be larger than the ejector pin heads.
Preferably, the compression plate has a periphery surrounding the opening adapted to contact the stripper plate as at least one of the compression plate and the ejector assembly are moved on the frame toward the other, and further includes pins for aligning the mold to the stripper plate, with the pins being in substantial alignment with the compression plate periphery.
In a related aspect, the present invention provides an apparatus for removing a casting comprising an electronic package substrate and an array of cast solder columns having a column pitch of less than 2 mm extending therefrom from the corresponding openings of a mold. The apparatus includes a frame and a removable mold containing a plurality of openings through a thickness thereof for casting a corresponding array of more than 2 solder columns having a column pitch of less than 2 mm and bonding the columns to the underside of an electronic package substrate when the substrate is disposed on the mold. A stripper plate is disposed on the frame for receiving the mold, the stripper plate containing more than 2 openings through a thickness thereof corresponding to at least some of the openings in the mold. An ejector assembly on the frame includes more than 2 ejector pins extending therefrom, with the ejector pins having a length at least as long as the sum of the thickness of the stripper plate at the stripper plate openings and the thickness of the mo
Bolde Lannie R.
Covell II James H.
Ahsan Aziz M.
DeLio & Peterson LLC
International Business Machines - Corporation
Pacheco Liza
Peterson Peter W.
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