Metal fusion bonding – Process – Preplacing solid filler
Reexamination Certificate
1998-04-16
2001-05-22
Dunn, Tom (Department: 3202)
Metal fusion bonding
Process
Preplacing solid filler
C228S041000
Reexamination Certificate
active
06234382
ABSTRACT:
The invention relates to a method for bonding solder balls to connecting points which are provided on a substrate in a predetermined pattern, wherein the solder balls are placed into holes provided in a plate-shaped element, which holes are each capable of accommodating one solder ball, and which are provided in said plate-shaped element in a pattern which corresponds with the pattern of the connecting points on the substrate, and wherein a combination of at least one substrate and a plate-shaped element containing solder balls is passed, by means of a conveying element, through a housing in which the solder balls are subjected to a heat treatment so as to be bonded to the substrate.
U.S. Pat. No. 5,442,852 describes a method for placing balls onto a substrate, wherein a membrane-like element is bonded to the substrate, which membrane-like element is provided with holes in a pattern which corresponds with the pattern of the connecting points on the substrate. Then solder balls can be picked up by means of an element which comprises a number of nozzles, which corresponds with the number of holes, which nozzles are arranged in such a manner as to correspond with the pattern of the holes, by generating a sub-atmospheric pressure in said nozzles, and the solder balls that have been picked up in this manner can be placed into the holes in the membrane that has been bonded to the substrate. The combination of substrate, carrier and solder balls thus obtained must subsequently be heated in order to melt the solder balls, so that the solder balls will bond to the connecting points. The means for carrying out this heating step cannot be derived from said U.S. Pat. No. 5,442,852.
U.S. Pat. Nos. 5,499,487 and 5,551,216 disclose devices for placing solder balls into plate-shaped elements which are provided with recesses for receiving solder balls. Said recessed plate-shaped elements are thereby fixed, together with a further plate-shaped element provided with through holes, to a supporting member which rotates about a horizontal axis of rotation, in such a manner that the two plate-shaped elements are spaced apart by some distance. Then the supporting element is caused to rotate with a view to rotating the plate-shaped element provided with through holes through a container in which solder balls are present, so as to place a solder ball into each of said through holes. Then the two plate-shaped elements are moved together and rotated by means of said supporting element, in such a manner that the recessed plate-shaped element will be positioned under the plate-shaped element provided with through holes, so that the solder balls will be transferred to the recesses of the respective plate-shaped element. The solder balls thus placed into the recessed plate-shaped element as intended can then be joined to a substrate comprising connecting points in some manner which is not described in detail in the aforesaid patent specifications.
U.S. Pat. No. 5,551,148 describes a method for placing solder balls onto a substrate, wherein a membrane-like element is used, which is provided with holes arranged in a predetermined pattern, which holes are filled with a soldering material or the like. Said membrane-like element is placed onto a substrate, in such a manner that the soldering material present in the holes will be positioned opposite the connecting points provided on the substrate. Said soldering material can be transferred to the connecting points by heating and pressing down said soldering material. All this is shown only diagrammatically in the said publication.
Japanese patent application No. 06209415 (publication No. 08056071) furthermore describes a method for providing solder balls, wherein an apertured plate is placed on a substrate. Then a frame-shaped member is placed on the apertured plate, and solder balls are deposited on the plate within the boundaries of said frame-shaped member.
Then the assembly of substrate, plate and frame and the solder balls accommodated therein is tilted in various directions and/or vibrated, in order to place a solder ball into each hole in the plate. Following that the frame and the excess balls are removed, and the substrate and the plate present thereon are passed through an oven in order to cause the solder balls to bond to the substrate.
From U.S. Pat. No. 4,951,401 and European patent applications Nos. 0 461 961 and 0 471 619 devices are known which are provided with endless conveyors, which are guided by pulley elements in such a manner that the conveyor moves along two substantially horizontal, superposed paths. The part of the endless conveyor that moves along the upper horizontal path is thereby passed through an oven construction. Substrates are placed on the upstream end of said upper part so as to be passed through the oven in order for the soldering material present on said substrates to be melted. The substrates must be removed at the end of said upper part.
U.S. Pat. No. 5,431,332 likewise describes a method for positioning solder balls on a substrate by means of an apertured membrane fixed to the substrate, wherein the solder balls are bonded to the substrate by means of a flux. Said patent specification thereby indicates that a substrate present on a pallet can be passed through an oven by means of a roller conveyor after removal of the apertured membrane. Said patent specification does not indicate how all this could be carried out in a controlled manner.
From the foregoing it will be apparent that according to prior art the correct positioning of solder balls and the bonding of said solder balls to a substrate are subdivided into a number of separate, usually complicated steps, whereby besides said separate steps known from the various publications, additional measures will have to be taken and means will be required for transferring the various products from one processing step to the other.
Usually the use of a flux for bonding the solder balls to the substrate is necessary thereby. The use of a flux generally leads to contamination of the substrates, however, so that a cleaning step is required after the soldering of the balls. Furthermore it is very difficult to apply the correct amount of flux at the location of the connecting points.
The object of the invention is to obtain a method of the kind referred to in the introduction, wherein the above drawbacks can be overcome.
According to the invention this objective can be accomplished in that the combinations, which each consist of at least one plate-shaped element and at least one substrate, are passed through said housing by said conveying element via lock mechanisms disposed near an inlet and near an outlet of the housing, in which housing a desired atmosphere is maintained, whilst inside the housing the solder balls are placed into the holes provided in said plate-shaped element.
By using this method it is possible to effect a continuous process of placing solder balls and bonding them in a sealed desired atmosphere, whereby it is generally possible to refrain from using a flux, in particular if the oxide film has been removed from the solder balls that are supplied.
According to another aspect of the invention the conveying element is made to move along two paths, one extending above the other, and on a part of the conveying element that follows a first one of said two superposed paths, at least one substrate is placed on a plate-shaped element supported by said conveying element, after which the combination thus formed, which consists of a plate-shaped element and at least one substrate, is moved by the conveying element and turned upside down at the transition to a second one of said two superposed paths, after which it is moved along the second path through the housing, whilst solder balls are supplied to the combination of a plate-shaped element and at least one substrate near the beginning of said second path, in a position of said combination in which the plate-shaped element is at least substantially positioned above said at least one substrate.
When this method is used, su
Kloosterboer Robert
Menschaar Hugo Franklin
Rischke Jorg Werner
Dunn Tom
MECO Equipment Engineers B.V.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Stoner Kiley
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