Patent Application
20090033337
The embodiments of the invention generally relate to temporary chip attach (TCA) carriers.
Temporary chip attach (TCA) carriers are substrates that are temporarily joined to an integrated circuit (IC) chip for the purposes of completing testing and burn-in. After testing and burn-in, the chip is removed by applying a shear force that breaks the small (e.g., 2.8 mil squared area) connections to the TCA carrier. This (TCA Carrier) can be accomplished, for example, with alumina carriers selectively plated with Ni bumps (e.g., 1.4×2 mils) using a thin film/plating process.
The embodiments herein provide a structure that tests such a chip using an interposer between the chip and the testing/burn-in substrate. The testing/burn-in substrate comprises internal circuitry and external contacts. The internal circuitry is connected to the external contacts by internal wiring within the substrate. Meltable conductors (e.g., solder connections) are connected to the external contacts of the substrate. The interposer has substrate contacts on a first side that are connected to the meltable conductors. With embodiments herein, the interposer is maintained apart from the substrate by the meltable conductors.
The interposer also comprises chip contacts on a second side opposite the first side. In place of the conventional temporary connections between the IC chip and the substrate, with embodiments herein the chip contacts of the interposer are adapted to temporarily connect to the integrated circuit chip being tested and burned-in. If desired, the chip contacts on the second side of the interposer can have different spacings/patterns than the substrate contacts on the first side of the interposer to allow non-similar chips and testing substrates to be used together. To make electrical contact between the IC chip and the substrate, the interposer includes conductive vias running from the first side to the second side directly connecting the substrate contacts to the chip contacts.
The interposer can comprise a laminated or solid structure, and can comprise alumina, glass ceramic, etc. The conductive vias comprise conductors, such as conductor filled Nickel plated vias. The meltable conductors on the different sides of the interposer can be different. Therefore, first meltable conductors can melt at a different temperature than second meltable conductors to allow the interposer to be separated from the testing substrate and from the chip during different processing steps.
These and other aspects of the embodiments of the invention will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating embodiments of the invention and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments of the invention without departing from the spirit thereof, and the embodiments of the invention include all such modifications.
The embodiments of the invention will be better understood from the following detailed description with reference to the drawings, in which:
The embodiments of the invention and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. It should be noted that the features illustrated in the drawings are not necessarily drawn to scale. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments of the invention. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments of the invention may be practiced and to further enable those of skill in the art to practice the embodiments of the invention. Accordingly, the examples should not be construed as limiting the scope of the embodiments of the invention.
As mentioned above, temporary chip attach (TCA) carriers are substrates used to temporarily join a chip for the purposes of completing test and burn-in. After the testing/burn-in, the chip is removed by applying a shear force that breaks the small (2.8 mil squared area) connections to the TCA carrier. In one example, the substrates can comprise alumina carriers selectively plated with Ni bumps made using a thin film/plating process. Alternative approaches can include selectively plated glass ceramic carriers; however such selective plating processes suffer from numerous technical hurdles yet to be solved. As an improvement to alumina substrates, the present invention uses conventional glass ceramic testing substrates in combination with an interposer.
More specifically, the present invention provides a glass ceramic carrier with an inexpensive interposer (alumina or glass ceramic) with small vias (e.g., <2 mils diameter) plated with Ni to temporarily attach to the chip. The interposer can also be a laminate (plastic, FR4, etc) carrier or a ceramic carrier.
As shown in
The meltable conductors 102/106 (e.g., solder connections) are connected to the external contacts of the substrate 100. The interposer 104 has substrate contacts on a first side that are connected to first ones of the meltable conductors 102 (e.g., substrate conductors). With embodiments herein, the interposer 104 is maintained apart from the substrate 100 by the first meltable conductors 102. The interposer 104 also comprises chip contacts on a second side opposite the first side. The second meltable conductors 106 connect the chip contacts of the interposer to the electrical contacts of the chip 108. To make electrical contact between the IC chip 108 and the substrate 100, the interposer 104 includes conductive vias 114 running from the first side to the second side directly connecting the substrate contacts to the chip contacts.
Thus, in place of the conventional substrate-based temporary connections to the chip (directly between the IC chip and the substrate), with embodiments herein the chip contacts of the interposer 104 are used to temporarily connect to the integrated circuit chip 108 being tested and burned-in. If desired, the chip contacts on the second side of the interposer 104 can have different spacings/patterns than the substrate contacts on the first side of the interposer 104 to allow non-similar chips and testing substrates to be used together.
The interposer 104 can comprise a laminated or solid structure, and can comprise, for example, alumina, glass ceramic, etc. The conductive vias 114 comprise conductors, such as conductor filled Nickel plated vias. The meltable conductors 102/106 on the different sides of the interposer 104 can be different. Therefore, first meltable conductors 102 can melt at a different temperature than the second meltable conductors 106 to allow the interposer 104 to be separated from the testing substrate 100 and from the chip 108 during different processing steps. The shear forces are shown in
The temperature/strength hierarchy between the chip join 106 and interposer join 102 can be accomplished by use of larger (e.g. 5 mil) solder balls 102 on the interposer 104 relative to the smaller solder balls 106 for the chip connection. The substrate conductors 102 can also be space transformers changing the size and spacing of the contacts to the substrate. The substrate conductors 102 can comprise, for example, a relatively higher temperature braze (e.g. CuSil or AuSn or Au—Au bonding) and/or an underfill 110, when compared to the chip conductors 106. This allows the chip to be warm sheared 120 off, while the substrate 100 and interposer 104 remain intact.
By using the interposer 104 with an otherwise conventional chip carrier 100 to create the TCA carrier, the problem of TCA join and shear is separated from the temporary chip attach problem (which now only applies to the interposer 104). The interposer 104 can be simple while the TCA carrier 100 by nature is very complex. It is more cost effective and better for carrier yield to move the temporary interconnect problem to the interposer 104, which is less expensive and easier to manufacture. The interposer 104 and the substrate 100 are joined using conventional bond/assembly techniques. The interposer 104 can be almost any suitable material, such as glass ceramic, laminate, etc.
The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments of the invention have been described in terms of embodiments, those skilled in the art will recognize that the embodiments of the invention can be practiced with modification within the spirit and scope of the appended claims.
