Cleaning and liquid contact with solids – Processes – For metallic – siliceous – or calcareous basework – including...
Reexamination Certificate
2002-02-14
2004-06-15
Carrillo, Sharidan (Department: 1746)
Cleaning and liquid contact with solids
Processes
For metallic, siliceous, or calcareous basework, including...
C134S002000, C134S019000, C134S021000, C134S026000, C134S028000, C134S029000, C134S034000, C134S036000, C134S041000, C134S042000, C134S902000
Reexamination Certificate
active
06749691
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is generally related to the field of cleaning metallic components. More specifically, the invention relates to cleaning metallic arrays, more particularly metallic arrays in electronic components such as integrated circuit flip-chip packages, and other packages.
2. Related Art
In the manufacture of integrated circuits and their various packages, residues are sometimes left from the manufacturing process on metallic components, or are generated prior to or during storage of the products. If the metallic components of the product have a residue from the manufacturing process, or contain residue generated after the manufacturing process while waiting for use, there exists the possibility that the metallic components of the product may not properly perform their intended functions.
Aside from performance, the appearance of the product may not be what is desired, or presumed by the user, due to instability of the product in the presence of the residue. For example, the electrical performance may not be a problem, but a discolored appearance may be enough for a customer to reject the product. Therefore, it has become imperative to find a way to clean discolored metallic arrays to remove residues that might have these deleterious effects.
As well stated in U.S. Pat. No. 5,759,285, a myriad of solder structures has been proposed for the interconnection of one electronic structure to another. Typical surface mount processes form the solder structures by screening solder paste on conductive, generally metallic pads exposed on the surface of a first electronic structure or substrate. A stencil printing operation is used to align the contact mask to the pads. The solder paste areas on the screened substrate are then aligned to corresponding pads on the electronic structure or board to be connected thereto. After alignment, the substrate and board go through a reflow operation to melt the solder paste and create a solder bond between the corresponding pads on the substrate and board.
The '285 patent describes other known interconnect technologies that use solder balls rather than a solder paste to provide the solder connecting structures. By using plated or evaporated solder balls, a more exact and somewhat greater quantity of solder can be applied than through screening. The solder balls are aligned and are held to a substrate and melted to form a solder joint on a conductive pad of the substrate. The use of solder ball connectors has been applied to the mounting of integrated circuit chips using the so-called C4 (control collapse chip connection) technology since the method and structure were first described and patented in U.S. Pat. Nos. 3,401,126 and 3,429,042. More recently, larger solder balls have been used in surface mount technology to attach single or multichip packages to circuit cards in so-called ball grid array or BGA technology. Regardless of the form of the solder connection or the method of making the solder connection, there are typically three stages at which cleaning of the solder surface may be essential. First, during deployment of the solder prior to making the connections, processing of solder may leave undesirable residues. For example, in evaporating or plating of solder balls for flip-chip (C4) connection or BGA module, photoresist or plating bath residues may be left which will interfere with proper solder wetting of the pads. Second, to maintain the alignment of the solder to the pads on the substrate or card and to allow good wetting of the solder on the pads, flux is most often used and will need to be removed to avoid leaving corrosive contaminants on the packaging assembly. Finally, rework of part-good assemblies requires special handling, which may require a cleaning step that assures the reliability of the package. For example, removal of a reworkable epoxy underfill, as described in U.S. Pat. No. 5,512,613, which is assigned to the present assignee, requires a cleaning process, which does not attack the C4 solder joints. Unfortunately, however, removal of the flux and flux products and cleaning of the solder is a difficult task because the cleaning process may itself be corrosive to the solder and/or electronic component. Additionally, dissolution of the solder can occur resulting in a smaller amount of solder forming the solder bond and cause disposal problems since the solders are generally lead/tin alloys and their solutions pose an environmental threat if discharged.
The solution to many of the problems evidenced in the '285 patent are achieved by a composition and method for cleaning solder to remove flux, flux reaction products, contaminants, residues from manufacturing operations, e.g., plating bath and photoresist residues and the like without any significant dissolution of the solder. The composition comprises a solution of a non-aromatic sulfonic acid and a substituted alcohol preferably a substituted aliphatic alcohol. The non-aromatic organic sulfonic acid is preferably methanesulfonic acid (MSA) and the alcohol 2,2,2-trifluoroethanol. The method of the '285 patent uses the above composition by applying the composition to the solder to be cleaned in any suitable way, e.g., by immersion in a bath at a temperature of about 25 to 75° C., or higher, preferably 50 to 70° C. for 1 to 120 minutes, preferably 5 to 60 minutes. Immersion may be performed under an inert cover (e.g., N
2
) but this is apparently not necessary.
U.S. Pat. No. 6,250,318 describes the art of cleaning using conventional washing equipment. The equipment generally consists of multiple zones of treatment; namely, a wash zone, a rinse zone and a dry zone. The wash zone typically contains a prewash section, a wash section and an air isolation section. In addition, there is a rinse section that typically includes a first rinse section to wash away the chemical from the wash section, a rinse section, a final rinse section and an isolation section. The final drying section generally contains an air isolation section, and the heated air-dry section. A central exhaust system located at the top of the entire apparatus acts to extract fumes generated from the washing actions, which are extracted by the central exhaust blower external to the cleaning apparatus. There is also a conveyor transport system that runs across the entire length of the various zones of treatment. This conveyor carries the device to be cleaned and moves the devices through the various treatment zones for cleaning and drying. The patent mentions that conventional cleaning equipment in the art generally include commercial spray nozzles attached to a spray manifold or hose, and held across the path of the device to be washed and cleaned. These nozzles are usually very large and bulky in diameter and provide various types of spray cones and angles of discharge. When these nozzles are attached a cross the spray manifold or hose, they cannot achieve close pitching when attached in a straight line. Thus spray angle coverage is the only means by which these spray nozzles reach the entire surface of the devices to be cleaned. This spray angulation causes the edges of the devices to experience a decrease in fluid energy as in the decrease of mass momentum of fluid motion. Advancement in miniaturization of semiconductor chips with the creation of micro-ball grid area packages and chip scale packages has seen the input-output interconnect leads being replaced by solder balls, with a pitch of around 1.0 to 1.5 mm. With the bulky size of the spray nozzles, cleaning of such closely packed devices become ineffective.
U.S. Pat. No. 6,203,637 describes use of a cleaning process. During the so-called “packaging” of integrated circuits, several operations are distinguished which comprise a bonding of surfaces: 1. The individual integrated circuits are cut out of a silicon wafer and are applied to semiconductor system carriers and are bonded with these (so-called die bonding). The semiconductor system carrier surface is normally made of copper or of nic
Fisher Matthew L.
Misra Ashutosh
Air Liquide America L.P.
Carrillo Sharidan
Russell Linda K.
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