Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Assembly of plural semiconductive substrates each possessing...
Reexamination Certificate
2002-09-16
2004-02-24
Thompson, Craig A. (Department: 2813)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Assembly of plural semiconductive substrates each possessing...
C438S118000, C438S598000
Reexamination Certificate
active
06696319
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a method of attaching semiconductor devices with contact devices on a switching device and to an apparatus including a switching device and a semiconductor device attached according to the method.
The contact devices of semiconductor devices may be applied to the latter already at wafer level (wafer level package). By the subsequent sawing of the wafer, individually separated semiconductor devices (hereafter referred to as components) are obtained. The attachment (hereafter also referred to as placement) of such components on the switching devices conventionally takes place by flip-chip technology. The contact devices are provided on the component, for example, as spherical solder bumps measuring approximately 0.1 mm in diameter of eutectic Sn—Pb solder. These solder bumps are soldered to contact areas lying on the surface of the switching device opposite the solder bumps during placement of the component. The soldering achieves the effect that the component is both electrically bonded and mechanically attached.
A disadvantage of such a method is the rigidity of the solder or the soldered connection under thermal loading of the component soldered on the switching device. The coefficient of thermal expansion of the component and of the switching device differ by several ppm/K, typically, approximately 15 ppm/K. In the case of a permissible temperature range for the component of −10° C. to +25° C., this corresponds to a thermally induced expansion of the component, on one hand, and the switching device, on the other hand, differing by approximately 45 &mgr;m. Due to the rigid soldered connections, the material of the component cannot contract and expand in a way corresponding to the thermal conditions. Thermomechanical stresses occur in the component in the region of the contact devices. These stresses may lead to tearing away of the soldered connection or damage in the electrical structures of the component and failure of the component.
Such a problem is conventionally solved by underfilling the placed component with an underfiller. The underfiller is pressed as a viscous paste between the component and the switching device after placement, by following the contours of the component, and is subsequently cured. If a placed component that has been so underfilled is subjected to thermal loading, the thermally induced mechanical stresses are distributed evenly over the entire surface of the component and the soldered connections are relieved. Disadvantages of the underfilling method are the expenditure, which the process of underfilling as such requires during production and the requirements on the underfilling itself.
In the case of a conventional possible way of avoiding the underfilling of components, flexible electrical contact elements are already provided at wafer level as contact devices on the semiconductor device. For such a purpose, a basic body several 10 &mgr;m high of an initially plastic polymer, preferably, silicone, is applied per contact element by a template to the surface of the semiconductor device facing the switching device and is subsequently cured. After that, the crest of the spherical basic body of the now elastic polymer is metallized and a conductor track is subsequently provided between the metallized crest and a bonding pad by a conventional technique.
If a component provided with such of flexible contact elements is soldered, the electrical connection remains mechanically flexible. Under thermal loading, the material of the component and of the switching device can expand differently. The elastic basic body of the contacts absorbs the thermally induced mechanical stresses and the thermomechanical loading of the semiconductor device and of the soldered connection is significantly reduced.
A disadvantage of such a method is the fact that the solder can creep onto the conductor track between the crest of the contact element and the bonding pad during the soldering process. A conductor track covered with solder loses mechanical flexibility and can be interrupted by the mechanical stresses occurring under thermal loading.
International publication WO 00/54321 describes a method of attaching a semiconductor component on a chip carrier, in which, at least during the soldering of the contacts of the semiconductor component to the contact devices of the chip carrier, contacts of the semiconductor device that do not have any electrical function are adhesively bonded to the surface of the chip carrier.
U.S. Pat. No. 5,148,266 to Khandros et al. discloses soldered connections between a semiconductor component and a substrate, with flexible contact devices being fixed at one end of the semiconductor component and soldered on the substrate at the other end. In such a case, however, thermally induced mechanical stresses load and fatigue the soldered joint between the substrate and the flexible contact element.
U.S. Pat. No. 5,885,849 to DiStefano et al. describes a method in which these soldered joints are provided in a circular and concavely constricted manner, whereby the mechanical stresses at the soldered joint are minimized. Along with the flexible contacts disclosed, inter alia, from DiStefano et al., a series of further flexible contact elements also exist in the art.
Novitsky, J.; Miller, C.: Wafer-level CSP, wafer-level assembly/test: Integrating backend processes. In: Solid State Technology, February 2001, pages 78-85, discloses flexible contact devices including a gold wire, which are thermosonically applied to the contact areas (pads) of the semiconductor component.
German Published, Non-Prosecuted Patent Application DE 100 16 132 A1 discloses flexible contact elements, on which an electrical contact is disposed on the tip of a cone of an elastic material.
U.S. Pat. No. 5,783,465 to Canning et al. discloses a similar contact device, in which the material of the cone is a polymer.
A semiconductor component described in U.S. Pat. No. 5,950,072 to Queyssac likewise has flexible contact elements. The flexibility is obtained by the fact that solder balls (solder bumps) provided for the soldering are attached on contact areas located on the semiconductor element by a conductive, thermoplastic adhesive.
All the methods and configuration mentioned share the common feature that the electrical contact elements of the substrate and semiconductor element are ultimately soldered to one another, or have been soldered.
A general disadvantage of soldered connections is also that of the high soldering temperatures, in particular, when novel, lead-free solders are used. The soldering temperatures of 240° C. occurring in such a case lie well above the required temperature range of the component in the application, subject it to considerable loading and may lead to the failure of the component.
If a defective soldered component has to be removed again from the switching device, it has to be desoldered. In addition, the remains of the soldering agent on the contact areas have to be removed.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method of attaching semiconductor devices on a switching device and such a semiconductor device that overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that in which the electrical contact devices of the semiconductor device and of the switching device remain free of solder.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method of attaching a semiconductor device on a switching device, including the steps of providing a semiconductor device with at least two electrical contact devices on a surface, providing a switching device with at least two electrical contact devices on a surface, forming the electrical contact devices on one of the two surfaces as flexible contact elements having a given expansion in a compressed state of the flexible contact elements, forming the electrical contact device
Frankowsky Gerd
Meyer Thorsten
Blum David S
Greenburg Laurence A.
Infineon - Technologies AG
Mayback Gregory L.
Thompson Craig A.
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