Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Assembly of plural semiconductive substrates each possessing...
Reexamination Certificate
2001-02-09
2003-04-29
Cuneo, Kamand (Department: 2829)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Assembly of plural semiconductive substrates each possessing...
C438S119000, C438S127000
Reexamination Certificate
active
06555414
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for assembling semiconductor devices on a substrate, such as a PCB substrate (printed circuit board), using a flip-chip assembly technique.
BACKGROUND OF THE INVENTION
Printed-circuit-board (PCB) assemblies, such as for telecommunications applications, are designed and produced with a high reliability as an important criterion. Therefore the technologies, applied in these assemblies, are often limited to well established and qualified technologies like reflow and wave soldering of standard SMT (surface-mount-technologies) and through-hole components. However, increasing demands for miniaturization, higher functionality, higher number of pins and higher frequencies put pressure on the telecommunications equipment manufacturers to introduce more advanced packaging technologies such as BGA (ball-grid-array), CSP (chip-size-package) and flip-chip assembly. These assembly techniques must cope with the requirements of, for example, larger chip size, increased number of pins or bonding pads, smaller pitch size, i.e. the distance between adjacent or neighboring pins or bond pads.
Flip chip bonding technologies provide a high package density and electrical performance compared to other LSI (large-scale-integration) packaging technologies. Several flip chip bonding techniques have been developed, mostly based on solder bonding of the chip to the substrate. According to the conventional flip chip assembly processes, the chip is attached to the substrate connecting the bonding pads by reflowed solder bumps. Afterwards the underfill material is dispensed alongside the edges of the bonded chip and allowed to flow in between the bonded chip and the interconnect substrate by means of capillary action. Finally, the underfill material is cured. The underfill material is the material used to fill the fixed stand-off gap between the chip and the substrate and in between the solder bumps connecting both parts.
In “low-cost High throughput Flip Chip Processing” by D. Baldwin et al. in “Advance Packaging Magazine”, January 2000, an alternative flip chip solder based bonding technique is proposed. First, a controlled volume of underfill material is stencil printed over the bonding pads. Next, solder paste is printed onto the board or substrate. Then, chips or SMT components are placed onto the substrate, having the chip bumps aligned to the bonding pads, compressing the liquid underfill material until the components make sufficient electrical and mechanical contact with the substrate. Finally the solder bumps are reflowed and the underfill material is cured. Although this alternative partly eliminates the time-consuming step of having the underfill material flow from the edge underneath the bonded chip, the proposed process still uses lead-bearing solder to form an electrical connection between the SMT component and the PCB-substrate.
In modern electronic assemblies, attempts are made to replace Pb/Sn solder with a number of alternative materials. This trend is driven by environmental reasons but also by the need to assemble components having finer or smaller pitch size. Among these alternative materials, leadless solders and adhesives are the most prominent candidates. With respect to the adhesives one distinguishes anisotropic conductive adhesives (ACAs), isotropic conductive adhesives (ICAs) and non-conductive adhesives (NCAs). An ACA consists merely of an electrically isolating NCA, wherein conductive particles, e.g. Ni/Au coated resin spheres, are dispersed. The content of dispersed conductive particles is limited to a few weight percent, and the particles are not linked to form chains. These particles form, after curing, a conductive path in a direction perpendicular to the substrate and the bonded component. An ICA also consists of an NCA but contains a very high content of conductive particles, e.g. silver flakes. After curing of the adhesive, the ICA therefore conducts isotropically.
In “Evaluation of Isotropic Conductive Adhesives (ICA) for Solder Replacement” by R. Pernice et al. in “International Society for Hybrid Microelectronics (ISHM)” Proceedings 1994, pp. 561-565, adhesives are used to bond coarse pitch components such as chip capacitors and resistors on a standard FR4-laminate substrate. Several ICA's were used to create an adhesive junction between the bonding lands on the substrate and the bonding pads of the SMT components under test. The adhesive junction is established by dispensing the adhesive on the bond pad metallizations, mounting the chip onto the bond pads and applying an appropriated heat and/or pressure process. The author reported non-consistent electrical stability or even mechanical failure of the adhesive junctions.
AIMS OF THE INVENTION
An aim of the present invention is to offer, in comparison to the state of the art, a simplified, reliable and cost-effective assembly process.
In particular, the invention aims to present a reliable assembly process, employing adhesives, applicable for all type of substrates, even for cheap, low-temperature substrates.
The invention further aims to offer a reliable assembly process, employing adhesives, applicable for mounting fine pitch components.
Finally, the invention aims to form units where both advanced (i.e. according to the invention) and classical (i.e. solder based) assemblies are present on the same PCB or other substrate. For such “mixed assembly” units, the invention proposes an assembly technique compatible with the classical one. One can hence choose the most appropriate assembly technique for each specific component to be attached on a substrate.
SUMMARY OF THE INVENTION
The present invention relates to a process for manufacturing an apparatus comprising at least one substrate and at least one component. In one aspect of the invention, an underfill material is applied to the substrate prior to the fusing or bonding of the substrate to the component. Thereafter, the substrate is bonded or fused to the at least one component. Through the process of bonding, electrical contact is made between the substrate and the at least one component. In one embodiment, electrical contact is made between bonding pads on the substrate with bonding pads on the component. There are several methods of bonding the substrate to the component including exerting a mechanical pressure so that contacts on the substrate and contacts on the component are bonded using an isotropically conductive adhesive, i.e. ICA. An alternate method is using soldering to bond the substrate with the component. When soldering, mechanical pressure may also be used for bonding.
In another aspect of the invention, a process for manufacturing an apparatus comprising at least one substrate and at least one component is disclosed. The component is attached to and in electrical contact with said substrate, characterized in that said process comprises the following steps:
providing a substrate, comprising on its surface a plurality of metal areas, called bonding pads or contact pads,
providing a component, comprising a plurality of metal areas, such as pins or bumps, also called bonding pads or contact pads, said bonding pads on said component corresponding to at least one group of said bonding pads on said substrate,
dispensing an adhesive onto said bonding pads of said substrate or onto said bonding pads of said component,
drying said ICA,
applying an underfill material in a predefined pattern on an area situated between said bonding pads of said substrate,
aligning said component so that said bonding pads of said component are directly above one group of bonding pads of said substrate,
exerting a mechanical pressure on said component, while maintaining said mechanical pressure and said predefined distance, performing a curing step, also called a thermocompression step, to cure said adhesive (e.g., isotropically conductive adhesive) and said underfill material (NCA) thereby creating electrical contacts between said component and said substrate.
According to an embodiment, the adhesive used is an
Stoukach Sergei
Vandecasteele Bjorn
Vanfleteren Jan
Cuneo Kamand
Geyer Scott B.
Interuniversitair Microelektronica Centrum vzw
McDonnell & Boehnen Hulbert & Berghoff
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