Metal fusion bonding – With means to juxtapose and bond plural workpieces – Plural discrete workpieces
Reexamination Certificate
2000-02-07
2001-01-30
Ryan, Patrick (Department: 1725)
Metal fusion bonding
With means to juxtapose and bond plural workpieces
Plural discrete workpieces
C228S004100, C228S013000, C228S044300, C228S051000
Reexamination Certificate
active
06179196
ABSTRACT:
FIELD OF INVENTION
The present inventions relates to soldered connection between bumps of area array components, and contacts on circuitized rigid organic substrates. More particularly the invention is related to replacing such components including removing area array components, redressing area array component sites, placing replacement components on the sites, and reflowing to solder the bumps of the replacement area array components to the contacts.
The following background is provided to assist those skilled in the art to utilize the invention of the Application and is not an admission regarding priority or statement that a search has been conducted.
BACKGROUND
U.S. Pat. Nos. 3,401,126 and 3,429,040 to Miller suggest connecting integrated computer (IC) chips by a grid array of C4 joints to ceramic substrates.
Fabrication of rigid organic circuit boards are suggested in U.S. Pat. Nos. 3,554,877; 3,791,858; and 3,554,877.
U.S. Pat. No. 5,024,372 to Altman suggests forming solder pads by using a squeegee to force paste onto contact pads at holes in a thick layer of solder resist; and U.S. Pat. No. 5,211,764 to Degani suggests printing solder through a stencil for connecting flip chips.
“Ball Grid Arrays: the Hot New Package” by Terry Costlow and “Solder Balls Make Connections” by Glenda Derman both in
Electronic Engineering Times
, Mar. 15, 1993, suggest using solder balls to connect ceramic and flexible chip carriers to circuit boards.
U.S. Pat. No. 5,207,372 to Funari et al. suggests a head for heating a semiconductor chip and applying force against the top surface of the semiconductor chip to form solder joints between 97/3 Pb/Sn solder bumps on the bottom surface of the chip and contacts on top of an epoxy resin circuit board reinforced by fiberglass. A backing plate is shown on the opposite side of the board from the connection.
U.S. Pat. No. 5,178,315 to Konno et al. suggests a pusher for pushing a push head against a component (IC chip) on a substrate and a supporting device with a support head and spring 42 for supporting the substrate on the opposite side of the substrate from the component. During soldering using light beams, “the push head and support head restrain the substrate from thermal deformation.”
U.S. Pat. No. 5,317,803 to Spigarelli et al. suggests a device for pressing the peripheral leads of and IC device against a printed circuit board during soldering.
U.S. Pat. No. 4,552,300 to Zovko et al. suggests a soldering-desoldering device including a ceramic housing with an open end which rests on the surface of a printed wiring board enclosing a leadless chip carrier and a ceramic heater assembly with an internal passageway. The housing interior conforms to the carrier and the heater conforms to the interior of the housing and slides within the housing. The heater assembly is lowered close to the carrier, pressurized air is introduced between the heater and housing, heated, and directed to the joints at the periphery of the carrier module. A vacuum is applied to the passageway to remove the air to prevent leaking between the housing and board.
The entire disclosures of the above citations are incorporated herein by reference for convenience.
OBJECTS OF THE INVENTION
It is an object of the invention to provide a simple mechanism and method for replacing area array components surface mounted to a rigid organic substrate.
It is an object of the invention to apply enough heat to such components to reflow solder paste to attach such components.
It is an object of the invention to apply enough heat to such components to soften solder joints to easily remove such components.
It is another object to apply such heat to such component while minimizing the heating of the substrate to prevent damaging the substrate or warping the substrate.
It is another object of the invention to hold the substrate flat while heating a component to be replaced and while reflowing solder for attaching a replacement area array component.
It is another object of the invention to prevent mechanical damage to the substrate surface by the holding apparatus during replacement of such area array components.
It is another object of the invention to prevent excessive heating of adjacent components which could damage the adjacent components or damage connection joints between the adjacent components and contacts of the substrate.
In the following description of the invention the term “area array component” is used for components such as ball grid array modules and flip chips in which multiple bumps along the periphery of an attachment surface of the component define a peripheral boundary of bumps and other bumps are spaced significantly inwardly from the boundary.
Also, the word “bumps” is used to refer to terminals of round cross section extending from the attachment surface including C4 bumps, eutectic bumps, eutectic coated C4 bumps, solder coated copper balls, and spherical preforms of high temperature solder.
Also, the term “rigid organic substrate” refers to substrates of organic materials that also include rigid fillers such as reinforcing fibers such as fiberglass which result in a substrate much more rigid than similar unfilled substrates.
SUMMARY OF THE INVENTION
It was discovered by applicants that locally heating a ceramic ball grid array chip carrier sufficient to reflow eutectic Pb/Sn solder to attach the component caused local warping of a FR-10 circuit board at the carrier due to temperature gradients through the board and the warping prevents reliable soldered connection of the inner balls to connection pads on the board. The most likely defect would be a surface to surface connection which could later vary in resistance or even separate to form an open circuit. This local warping had not been a significant problem in replacing peripheral leaded components such as quad flat packs. The maximum separation between contacts and bumps for area array components is significantly greater than the maximum separation between leads and contacts for other surface mount components of similar size.
The bumps of area array components are much less flexible in the direction perpendicular to the circuit board than peripheral leads such as gull wing leads or J-leads. Because of the greater stiffness and restraint of greater thermal displacement, the force between the contacts and bumps of an area array component during cooling and any subsequent reheating for replacement, is much higher than between the contacts and leads of such peripherally leaded surface mount components.
Thus during cooling after attachment and any subsequent heating for removal, the contacts on the circuit board could potentially be pulled off from the circuit board due to the high forces caused by restraint of the local warping of the board. During cooling, components could be damaged by the high forces on joints. Also, good components that need removal for flawed joints or for design changes, could potentially be damaged by the warping during removal because of high forces on individual joints during heating.
In the invention of applicants an area array component selected for replacement is heated to remove the component and then a replacement area array component is heated to reflow attach the replacement component.
In the invention, during heating and subsequent cooling, local warping is restrained to prevent damaging the board or components. Preferably, the holding means does not restrain the component so that the component is free to move into better alignment due to surface tension of the solder during the heating of the component and board.
In the invention in order to prevent damage to joints of adjacent components, the open end of a nozzle duct seals against the surface of a substrate without damaging the surface. Preferably the nozzle gimbals so that the angle of the end of the duct matches the angle of the surface of the substrate to closely fit the surface. Preferably the end of the nozzle is covered by an elastic material to deform over small irregularities and waves in order to closely fit the surface.
Other
Heim Craig G.
Lewis Russell H.
Pierson Mark V.
Puttlitz Karl J.
International Business Machines - Corporation
Pittman Zidia T.
Pivnichny John R.
Ratner & Prestia
Ryan Patrick
LandOfFree
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