Metal fusion bonding – Process – Preplacing solid filler
Reexamination Certificate
2000-01-21
2001-02-13
Ryan, Patrick (Department: 1725)
Metal fusion bonding
Process
Preplacing solid filler
C228S180220, C228S248500, C438S613000
Reexamination Certificate
active
06186392
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to semiconductor manufacture, and more particularly to an improved method and system for forming contacts on a semiconductor component by aligning and attaching ferromagnetic balls to bonding sites on the component.
BACKGROUND OF THE INVENTION
Semiconductor components, such as wafers, dice and packages can include external contacts in the form of solder balls. For some components, such as chip scale packages, the balls can be arranged in a dense array, such as a ball grid array (BGA), or a fine ball grid array (FBGA). The balls provide a high input/output capability for a component, and permit the component to be surface mounted to a mating component such as a printed circuit board (PCB).
One conventional method for attaching the balls to a component substrate uses a solder reflow process. With this method the substrate can include bonding sites, such as bond pads, or land pads, on which layers of flux are deposited. A platen can be used to hold the substrate, while the flux is deposited on the bonding sites in a required pattern. After depositing the flux layers, the solder balls can be placed on the flux layers, and a convection furnace used to reflow the flux layers. After cooling, a permanent solder bond is formed between the bonding sites and solder balls.
Because the solder balls have a natural attraction for the flux layers, the alignment step is facilitated. One problem with this method is that during the heating step, the flux can liquefy prior to the balls. As the flux liquefies, the balls are free to move and can roll off the bonding site. This can cause missing and mis-aligned balls, and also defective components. Defects can lower throughput in a production process, and necessitate expensive rework procedures.
In order to maintain the balls in alignment with the bonding sites, a ball retaining plate is sometimes employed during the aligning and heating steps. For example, the ball retaining plate can include separate cavities for retaining each solder ball. A vacuum can also be applied to the cavities to provide a positive force for holding the balls in the cavities. U.S. Pat. No. 5,118,027 to Braun et al. discloses a reflow process in which a ball retaining plate and vacuum are used to hold the solder balls.
In general this method, can be performed on balls that have a diameter of about 0.012-in (0.305 mm) or larger. A center to center pitch of the balls can be about 0.018-in (0.457) mm. However, as the balls become smaller, and the spacing between the balls become tighter, it becomes more difficult to align and attach the balls.
Another problem with prior art aligning and attaching methods is the difficulty of fabricating ball retaining plates with the required feature sizes. For example, for fine ball grid array (FGBA) components, the balls can have a diameter as small as 0.005-in (0.127 mm), and a center to center pitch of only about 0.008-in (0.228 mm). It is difficult to make ball retaining plates with the required features sizes using conventional machining processes.
Balls can also be attached to bonding sites by laser reflow, soldering, brazing, welding, or applying a conductive adhesive. In each case some method must be employed to align and maintain the alignment of the balls to the bonding sites. A solder ball bumper, for example, employs a tool to precisely position pre-formed balls on a bonding site, and a laser to initiate reflow. However, solder ball bumpers, and similar apparatus, are relative expensive to purchase and maintain, and can have a limited throughput for volume semiconductor manufacture.
The balls, rather than being pre-formed members, can also be formed directly on the bonding sites using a deposition process such as screen printing, evaporation through a mask, or chemical vapor deposition. These deposition methods each have limitations with respect to the size and spacing of the balls, and also require relatively expensive equipment.
In view of the foregoing, there is a need in the art for improved methods and apparatus for forming contacts on semiconductor components.
SUMMARY OF THE INVENTION
In accordance with the present invention, an improved method and system for forming contacts on a semiconductor component are provided. The semiconductor component can comprise a semiconductor wafer, a semiconductor die, a semiconductor package, a chip scale package, or a separate substrate (e.g., BGA substrate, PCB) for a semiconductor component. The semiconductor component includes a pattern of bonding sites, such as bond pads, wherein the balls will be attached to form the external contacts for the component.
The method, simply stated, comprises aligning and attaching ferromagnetic balls to the component using magnetic force. The method can be performed using a holder that includes magnets having a pattern matching that of the bonding sites on the component. The holder can also include an alignment opening configured to retain the component, and to contact peripheral edges of the component to align the bonding sites to the magnets.
In an illustrative embodiment the balls are spherically shaped, and include a ferromagnetic core such as iron, steel, nickel, cobalt, titanium, aluminum or magnetic stainless steel, embedded in an outer solder layer. Alternately, the balls can comprise ferromagnetic particles embedded in a bondable matrix material, such as a polymer adhesive, or a solder alloy. As another alternative, the balls can comprise a unitary ferromagnetic metal formed in a spherical shape. As yet another alternative, the balls can comprise a ferromagnetic material covered with an electroconductive polymer adhesive.
In the illustrative embodiment the bonding step is performed by placing the component and the holder in a furnace heated to a temperature sufficient to reflow the balls. Alternately the bonding step can be performed using a focused energy source such as a laser, or a beam of high energy xenon light. In either case, because the balls are aligned with the bonding sites, and held on the bonding sites by magnetic force, solder flux does not need to be applied to the balls, or to the bonding sites. In addition, the balls can be pre-treated to remove surface oxides that inhibit the bonding process.
A system for performing the method includes the holder, a ball placement mechanism for placing the balls on the bonding sites, and a bonding mechanism, such as an oven, for heating and bonding the balls to the bonding sites. An alternate embodiment system includes a bonding mechanism which includes a focused energy source such as a laser, or a high-energy xenon light source. Another alternate embodiment system includes a focused energy source and a focused magnetic source.
REFERENCES:
patent: 3960279 (1976-06-01), Hartleroad et al.
patent: 4004261 (1977-01-01), Klingenberg
patent: 4346516 (1982-08-01), Yokuchi et al.
patent: 4801065 (1989-01-01), Colquitt et al.
patent: 4830264 (1989-05-01), Bitaillou et al.
patent: 4983804 (1991-01-01), Chan et al.
patent: 5118027 (1992-06-01), Braun et al.
patent: 5299730 (1994-04-01), Pasch et al.
patent: 5346775 (1994-09-01), Jin et al.
patent: 5401911 (1995-03-01), Anderson et al.
patent: 5447886 (1995-09-01), Rai
patent: 5531942 (1996-07-01), Gilleo et al.
patent: 5539153 (1996-07-01), Schwiebert et al.
patent: 5620927 (1997-04-01), Lee
patent: 5643831 (1997-07-01), Ochiai et al.
patent: 5674785 (1997-10-01), Akram et al.
patent: 5739585 (1998-04-01), Akram et al.
patent: 5816482 (1998-10-01), Grabbe
patent: 5839641 (1998-11-01), Teng
patent: 5841198 (1998-11-01), Chia et al.
patent: 5867082 (1999-02-01), Van Zeeland
patent: 5872400 (1999-02-01), Chapman et al.
patent: 5899737 (1999-05-01), Trabucco
patent: 5986348 (1999-11-01), Fukano
patent: 6100175 (2000-08-01), Wood et al.
Gratton Stephen A.
Johnson Jonathan
Micro)n Technology, Inc.
Ryan Patrick
LandOfFree
Method and system for forming contacts on a semiconductor... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and system for forming contacts on a semiconductor..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and system for forming contacts on a semiconductor... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2571978