Metal fusion bonding – Including means to apply flux or filler to work or applicator
Reexamination Certificate
1999-02-08
2001-07-24
Dunn, Tom (Department: 1725)
Metal fusion bonding
Including means to apply flux or filler to work or applicator
C228S260000, C228S262000
Reexamination Certificate
active
06264090
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a jet soldering system.
Various soldering schemes have been developed for bonding semiconductor integrated circuit (IC) chips to a substrate (e.g., a printed circuit board). In some schemes, a semiconductor IC chip is bonded to a substrate by applying a small solder bump to the bottom surface of the chip, aligning the solder bump with a bond pad on the surface of the substrate, and heating the solder bump until it reflows. In some other schemes, solder bumps are applied to bonding pads on a substrate; afterwards, electronic components are bonded to the substrate by positioning the components over the solder bumps and by heating and reflowing the solder bumps. Some schemes bond IC chips to a patterned layer of solder created by applying a thin layer of solder paste to a substrate through holes in a stencil, leaving a selected solder pattern on the substrate. Recently, solder jet systems have been proposed for depositing solder droplets onto a substrate in a selected pattern. Such systems include a solder droplet ejector, which may eject solder droplets on-demand or continuously. In one proposed continuous solder jet system, a droplet generator vibrates to form a stream of solder droplets; an electrical charge is applied to the droplets and the charged droplets are passed between charged deflection plates which selectively direct the droplets to a target surface or to a catcher system.
SUMMARY OF THE INVENTION
In one aspect, the invention features depositing a selected pattern of solder droplets onto a substrate on which one or more electronic components are to be mounted. There is relative movement between the substrate and a solder ejector along a scan axis. The droplets from the ejector are deflected along a fan axis that is transverse to the scan axis by selectively applying a charge to each droplet and passing the charged droplets through an electric field. The position on the substrate along the scan axis at which a droplet is placed is determined by the relative position of the substrate with respect to the ejector at the time at which a charge is applied, and the position of the droplet along the transverse fan axis is determined by the magnitude of the charge applied to the droplet. The substrate can be moved or the ejector can be moved to provide the relative movement along the scan axis.
In preferred embodiments, the substrate is continuously moved along the scan axis, which avoids delays that would otherwise be introduced by moving the substrate step-wise and reduces the time taken to deposit the pattern of solder droplets. In order to permit placing of droplets on a substrate axis (i.e., in a row, which might very well be parallel to a substrate edge and might otherwise be oriented parallel to the fan axis), the substrate axis is oriented at an acute operating angle with respect to the fan axis.
The components generating the electric field (e.g., plates) can be rotatable about an axis which is normal to the substrate in order to orient the substrate with respect to the fan axis by rotating the fan axis with respect to the scan axis. Alternatively, the substrate can be mounted at an angle with respect to the scan axis on its movable support in order to adjust the angle between the substrate axis and the fan axis.
Preferably the pattern of solder droplets is defined by coordinate pattern data (e.g., CAD data) referenced with respect to the substrate, and these data are transformed to coordinate pattern data referenced with respect to a substrate support. The coordinate pattern data, which are generally referenced with respect to perpendicular axes, are also transformed to angle-adjusted coordinate pattern data according to the acute operating angle.
The acute operating angle is desirably determined by transforming the coordinate pattern data to angle-adjusted coordinate pattern data for a plurality of potential acute operating angle values, determining positions of droplets and spacings between droplets along the scan axis for angle-adjusted coordinate pattern data for each of the potential acute operating angle values, and selecting the acute operating angle from the plurality of potential acute operating angle values based upon the spacings between droplets. By selecting the operating angle that has the largest value for the smallest spacing between two droplets, the permitted velocity along the scan axis can be maximized to minimize processing time. In addition, the spacings along the scan axis can be increased (with a corresponding increase in velocity) by adjusting the scan axis position values for the angle-adjusted data to accommodate an allowable error for placement of each droplet; the allowable error is determined by the difference between the user-specified maximum error for placing droplets and the significantly smaller maximum error of the printing equipment.
After selecting an acute operating angle, the angle-adjusted coordinate pattern data are used to control when charges are applied to the solder droplets being ejected and to control the magnitude of the charges.
In another aspect the invention features depositing a selected pattern of solder droplets onto a substrate by directing molten solder droplets from a solder ejector through an electrical field, selectively applying charges to the solder droplets prior to passage through the field in order to control deflection of the solder droplets to a desired position along a fan axis, and creating relative movement between the substrate and the fan axis. In some embodiments the fan axis is moved (e.g., by rotating plates providing the field with the ejector either fixed or rotatable) and in some others the substrate is moved (e.g., rotated). Preferably the relative motion is continuous.
Other features and advantages of the invention will become apparent from the following description of preferred embodiments and from the claims.
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Balog Robert J.
Muntz Eric Phillip
Orme-Marmarelis Melissa E.
Pham-Van-Diep Gerald C.
Dunn Tom
Mintz Levin Cohn Ferris Glovsky and Popeo P.C.
Speedline Technologies, Inc.
Stoner Kiley
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