Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Flip chip
Reexamination Certificate
1997-12-19
2001-02-13
Wong, Peter S. (Department: 2838)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Flip chip
C257S688000, C257S737000, C257S777000
Reexamination Certificate
active
06188138
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a mounting technology for aligning parts in electronic field, more particularly to a fast and easy self-aligned elastic high precision positioning, where one part has bumps, another part has V-grooves and the parts fit into each other.
DESCRIPTION OF RELATED ART
The technical evolution in the field of electronics, has resulted in a demand for faster and more compact systems. In many applications a compact structure combined with a low weight is in itself a requirement. The technical evolution also tends towards more complex systems involving a greater and greater number of components, which need to communicate with each other. In order to meet the requirement of quick access between different components for the new systems the length of the paths between different components of the system must be kept within certain limits. When the complexity of a system grows, the length of the paths between components also grows. In order not to exceed the maximum allowed distance between such components, these components have been built smaller and smaller and they have also been packed more and more densely.
The relative position of one part to another in a system is in many cases a critical task. For this purpose there is no existing technology offering an elastic high precision self alignment of a part at a micrometer or even sub-micrometer scale. Lateral and sometimes even 3-dimensional positioning requires the use of advanced aligning equipment to join parts together, also reliable methods and materials are needed to maintain their positions even under severe external conditions, such as temperature cycling. If parts in the system consist of materials with different thermal expansion coefficients, then solid joints may cause problems due to stresses arising from temperature variations. In the field of electronic and optronic production the demands on very accurate positioning are increasing with reduced dimensions and more advanced packaging. For example, thermal expansion may cause severe problems due to displacement of a laser used to output light to a single mode optical fiber. In another example, thermal expansion induced stresses will damage electrical interconnects to a die flip-chip mounted on a substrate of a different thermal expansion coefficient than the die itself. Another aspect is that as packages have increased number and complexity of the integrated circuits, IC:s, easy repair will be necessary to achieve sufficient yield.
Alignment has been achieved by using a surface, a wall corner extending from that surface and then securing the system by, e.g., glueing, soldering etc. If the aligned parts expand differently due to heating when they are in use different things may happen. If the fastening is very stiff, the expansion will cause stress and eventually some warping or possibly breakage. The alignment is at least lost in one dimension.
Consider the relative positioning of two individual parts. This can be and has previously been achieved by using grooves for registration, for example, V-grooves have been made by anisotropic wet chemical etching in silicon to fit with protruding structures such as balls, pins, or V-hills in the other part.
One way to get fine pre-alignment of flip-chips is to use mechanical placement equipment before soldering the two parts together.
Another way is to use the flip-chip soldering itself, which includes alignment features. The actual alignment determining solder joint has to be destroyed when separating and a new one formed for the replaced part.
Existing methods offer alignment with stiff joints, but these can cause expansion and mismatch problems, such as damage or sudden misalignment in one direction.
The U.S. Pat. No. 5,214,308, Masanori Nishiguchi et al., describes a micro aligning method, which is based on bumps and grooves. It describes alignment before permanent attachment to the base substrate. The bumps and grooves are not shaped exactly after like each other.
SUMMARY
This invention solves the problem of alignment of parts without using mechanical fine pre-alignment.
This invention has the ability to obtain and maintain very precise alignment in combination with elasticity to handle, e.g., expansion mismatch at a central or arbitrary point of the aligned parts by careful placement of the bumps and grooves. The grooves may be of 5 corner pentahedron or pyramidical form and the bumps may be of truncated 5 corner pentahedron or truncated pyramidical form. The invention does not need any fine pre-alignment since the alignment structures are very large compared to the precision they offer wherein the parts automatically will come into the right position when pressed together after a rough pre-alignment.
The present invention uses elastic material for the protruding parts to perfectly fit the V-grooves. To achieve this, the bumps are made of elastic material and shaped partly to the V-bumps by moulding. A mould is used as a mating part or a similar mould is used identical or similarly shaped as the V-grooves. Using these V-shaped bumps and grooves, the bumps will align automatically into the V-grooves when the two parts are brought together.
This solution has at least one fixed arbitrary point, which would be between two adjacent bumps and grooves in the plane of the surface of the two parts. The two parts can slide along each other. The movement in the perpendicular direction, i.e., height difference between the two parts, can be controlled by an external force or by the size of bump. This means that the bumps and V-grooves have good alignment in the X-Y plane and are also partially aligned along the z axis.
The non-permanent bumps in grooves alignment techniques automatically achieve high precision without the bumps acting as the joining part, provided that there is some other force pressing the two parts together. By using these types of parts they can be disassembled and continuously replaced without destroying the alignment features.
One advantage of the present invention is that continued high precision alignment of parts will be stable when external mechanisms cause effects on the parts.
Another advantage of the present invention is the changeability and replacebility of parts in the advanced packaging system.
Another advantage of the present invention is that the parts can absorb elastic changes and still be aligned along a line in the X-Y plane.
Another advantage of the present invention is that the parts can be reused and kept in alignment, even after a very large number of matings.
Another advantage of the present invention is that the bumps and grooves are formed to mate perfectly in order to perform maximum alignment.
Another advantage of the present invention is that manufacturing reproducibility is very high and uses simple techniques forecasting low production costs.
A further advantage of the present invention is that the invention results in very precise alignment and freedom of stress for micro parts produced using more or less standard planar techniques in combination with moulding of elastic compound.
A still further advantage of the present invention is that the invention can maintain alignment even if there is thermal displacement of parts.
The invention is now being described further with the help of the detailed description of the preferred embodiments and the attached drawings.
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patent
Bodo Peter
Hesselbom Hjalmar
Burns Doane Swecker & Mathis L.L.P.
Telefonaktiebolaget LM Ericsson (pub)
Tibbits Pia
Wong Peter S.
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