This invention relates generally to the field of electronic devices packaging and more particularly to a method and apparatus for attaching solder members to a substrate. 
Modern electronic components utilize numerous integrated circuits.  Often, these integrated circuits must be electrically connected to each other or to other electronic components.  One method for connecting integrated circuits to electronic components utilizes an area array electronic package.  Some examples of area array electronic package designs are a ball grid array electronic package and a flip-chip electronic package.  With a ball grid array electronic package, various input and output ports of an integrated circuit are typically connected via wire bonds to contact pads on the ball grid array electronic package.  Solder balls formed on the contact pads of the ball grid array electronic package are used to complete the connection to another electronic component, such as a printed circuit board.  Integrated circuits are also connected to electronic components through a flip-chip electronic package design.  The flip-chip electronic package is similar to the ball grid array electronic package in that solder balls are used to make a connection with other electronic components, such as a printed circuit board.  However, solder balls in a flip-chip design are attached directly to the input and output ports on the face of the integrated circuit.  Flip-chip packages do not require wire bonds.  One important step in the above described methods for interconnecting electronic components is the formation of solder balls on the ball grid array package or flip-chip electronic package. 
Several conventional methods exist for attaching solder balls to a ball grid array or flip-chip electronic packages.  Flip-chip solder bumps may be fabricated on the integrated circuit by evaporation or plating while the solder necessary for a ball grid array electronic package may be achieved by solder paste printing or vacuum loading preformed solder balls onto a substrate through the use of a vacuum chuck.  The use of a vacuum chuck to transfer preformed solder balls to the contact pads on the ball grid array package suffers several disadvantages.  For example, the minimum distance between solder balls that this method allows may be unacceptable in some applications.  Additionally, this conventional method may require two vacuum chucks because while one vacuum chuck is transferring solder balls to the ball grid array electronic package, the other is being filled.  The use of one or more vacuum chucks increases the expense associated with this method for forming solder balls on an electronic package.  Furthermore, if a solder ball is not transferred properly, any adjustment, such as adding a missing solder ball, must be made by hand. 
Another conventional method for attaching solder to a ball grid array or flip-chip electronic package utilizes a stencil placed on top of the package.  In a typical application, solder paste is applied on top of the stencil and then a squeegee is moved across the top of the stencil forcing the solder paste down through the holes until contact is made with the contact pads of the ball grid array or flip-chip electronic package.  This method also suffers several disadvantages.  For example, the stencil requires cleaning.  Additionally, the stencils tend to deteriorate because the solder paste may wear on the stencils.  Furthermore, the use of solder paste may be more expensive than the use of solder balls. 
Therefore, a need has arisen for a new method and apparatus that overcomes the disadvantages and deficiencies of the prior art.  The invention comprises a method and apparatus for attaching solder members to a substrate. 
According to one aspect of the invention, the method comprises the step of forming a decal.  The decal comprises a plurality of solder members.  The method further comprises aligning the decal with a substrate and transferring the solder members on the decal to the substrate. 
According to another aspect of the invention, a method for forming a decal for transferring solder member to a substrate comprises the step of forming a plurality of apertures in a substrate and placing a plurality of solder members on the substrate.  The method further comprises allowing the plurality of solder members on the substrate to enter the plurality of apertures to form a decal having a plurality of solder members. 
The invention provides a method for attaching solder members to a substrate that facilitates precise alignment of the solder members with desired locations on the substrate.  Because only the decal requires alignment, in contrast to aligning multiple solder members with desired locations on a ball grid array package, precise alignment of all solder members with desired locations on the ball grid array package may be made through one alignment process.  Missing balls are often a problem in conventional ball grid array production lines.  The invention may enhance the production efficiency and yield of non-missing balls by screening out defective decals before shipment to a vendor.  This screening process contrasts with conventional screening that may take place after attachment of solder balls to the ball grid array package. 
The invention also allows for the formation at a central site of solder member decals that may be shipped to remote locations for transferring the solder members to the ball grid array package.  Therefore, much of the equipment conventionally used to place solder on a ball grid array can be eliminated, which may reduce the cost of forming solder balls on ball grid arrays.  Any equipment required to produce the solder member decal may reside solely at a centralized location.  Formation of a solder member decal also facilitates delegation to third parties of a portion of the solder ball attachment process, which may further reduce costs.  Because the solder member decals may be formed without solder paste, the use of solder member decals does not expose the ball grid array package or other substrate to which solder members may be attached to the harshness of such a chemical process.  The use of preformed solder members eliminates the expense of using environmentally unfriendly chemicals.  The use of solder balls rather than solder paste also provides a more uniform distribution of solder and allows the use of various types of solder alloys.