Industrial Technology Research Institute

Taiwan Semiconductor Manufacturing Comp. Ltd.

Ling-Chen Kung

Szu-Wei Lu

Ruoh-Huey Uang

Kuo-Chuan Chen

Hsu-Tien Hu

Chun-Yi Kuo

Ying-Nan Wen

Jyh-Rong Lin

Tsung-Yao Chu

A method for forming a wafer level package that is equipped with solder balls on a top surface and encapsulated by a stress buffer layer of an elastomeric material is disclosed. The method can be carried by first forming a plurality of solder balls on bond pads provided on a top surface of a wafer and then forming an elastomeric material layer, or any other flexible, compliant material layer to encapsulate the solder balls. The tip portions of the solder balls is then substantially exposed by an etching process of either dry etching or wet etching such that the solder balls can be connected electrically to a circuit board. The present invention further provides a wafer level package that is formed with solder balls on a top surface encapsulated in an elastomeric material layer. The elastomeric material layer serves both as a stress buffer and a thermal expansion buffer such that the integrity and reliability of IC devices severed from the wafer can be maintained.

Method for forming wafer level package

The present invention discloses a dual-photoresist method for forming fine-pitched solder bumps on flip chips by utilizing two separate layers of photoresist, i.e., a first thin photoresist layer for patterning the BLM layers on top of the aluminum bonding pads and a second thick photoresist layer for patterning the via openings on top of the BLM layers to supply the necessary thickness required for the solder bumps. The first, thin photoresist layer permits an accurate imaging process to be conducted without focusing problems which are normally associated with thick photoresist layers. As an optional step, the present invention may further utilize a thin layer of non-leachable metal such as Cu or Ni for coating on top of the BLM layer and thus further improving the electrical characteristics of the solder bumps subsequently formed thereon. A majority of the BLM layer is removed with the first, thin photoresist layer and thus, in the final BLM removal process, only a very thin adhesion sublayer of the BLM layer needs to be removed and as a result, ensures a clean removal process without damaging the solder bumps already formed with a fine-pitch.

Method for forming solder bumps on flip chips and devices formed

A method for fabricating a wafer level package and packages formed are disclosed. In the method, an elastomeric material layer is first deposited on top of a passivation layer by a printing, coating or laminating method to form a plurality of isolated islands. The islands may have a thickness of less than 100 &mgr;m. Metal traces for I/O redistribution are then formed to connect the isolated islands with bond pads provided on the surface of the wafer such that one bond pad is connected electrically to one isolated island. On top of the metal trace is then deposited an organic material for insulation with the metal trace on top of the isolated islands exposed. After an UBM layer is formed on top of the metal traces that are exposed on the isolated islands, solder balls of suitable size may be planted by a plating technique, a printing technique or a pick and place technique to complete the wafer level package.

Wafer level packaging method and packages formed

A method for forming solder balls that have larger spacings between them and electronic devices containing such solder balls are disclosed. In the method, an additional layer of a leachable metal such as gold or silver is used between an under bump metallurgy layer and a solder bump subsequently formed. This allows the formation of the under bump metallurgy layer prior to the deposition of the solder material into a window formed in a photoresist layer. The present invention allows the underfill of a solder window, instead of an overfill which is normally required in a conventional method.

Method for forming fine-pitched solder bumps

The present invention discloses a method for forming a wafer level package by first providing a silicon wafer that has a multiplicity of IC dies formed on a top surface, each of the IC dies has at least one peripheral I/O pad formed in an insulating layer, then forming at least one via plug of a conductive metal with a top surface exposed on the at least one peripheral I/O pad, then coating a layer of an insulating material that has sufficient elasticity on the surface of the wafer prior to the deposition and forming of a metal trace on the elastic material layer, at least one area array I/O pad is then formed at an opposite end of the metal trace with a solder bump formed on the I/O pad before they are reflowed into a solder ball. The elastic material layer deposited under the metal traces acts as a stress-buffing layer such that an IC circuit of high reliability can be produced on a wafer level for the low cost fabrication of IC assembly.

Wafer level packaging method and devices formed

A method for forming solder balls that have improved height on an electronic substrate such as a silicon wafer and devices formed are disclosed. In the method, after solder bumps are deposited by a conventional method such as evaporation, electroplating, electroless plating or solder paste screen printing, the solder bumps are reflown on the substrate in an upside down position such that the gravity of the solder material pulls down the solder ball and thereby increasing its height after the reflow process is completed. It has been found that a minimum of 5%, and preferably about 10% height increase has been achieved. Another benefit achieved by the present invention novel method which is associated with the increase in the solder ball height is a corresponding increase in the pitch distance between the solder balls by at least 5%.

Growing community of inventors

Hsinchu, Taiwan

Ling-Chen Kung