Patent Application
20080060750
The invention may be more readily understood by referring to the accompanying drawings in which:
Like numerals refer to like parts throughout the several views of the drawings.
In one preferred embodiment, the electronic device placement process 150 includes the following stages: a penetrable carrier and second carrier alignment stage 106, during which the electronic devices on the penetrable carrier are aligned to the second carrier; an electronic device pinning stage 108, where the electronic devices are pinned to the second carrier using an array of pins; a penetrable carrier detachment stage 110, during which the penetrable carrier is moved away from the pinned electronic devices; and a pin array removal stage 112, where the pin array is moved away from the electronic devices that are now attached to the second carrier.
Portions of the electronic device transfer and attachment process described herein may be optional and the described process may include portions that are not needed for a particular application. Therefore, the following description should be read as illustrating exemplary embodiments of a novel electronic device transfer and assembly process as practiced in one preferred embodiment of the present invention and should not be read in a limiting sense. Specifically, the electronic device transfer and assembly process described herein is applied to the assembling of RFID devices, where electronic devices are chips that are being attached to strap leads.
With reference to
In one preferred embodiment, the penetrable carrier substrate 204 is in the form of a film and the film may have an adhesive disposed on one side. In this embodiment, no hole exists in the penetrable carrier substrate 204 until the carrier substrate is penetrated. In another preferred embodiment, the penetrable carrier substrate 204 is a mesh web with the adhesive layer 206 disposed on one side of the penetrable carrier substrate 204. The mesh web can be made from a material similar to the material that is used for silk screen printing. Typically the mesh web is woven from fibers. The fibers can be polyester, nylon, metal, etc. Further, in this embodiment the adhesive layer 206 may be coated onto the penetrable carrier substrate 204 (i.e., mesh web) such that adhesive will penetrate into holes in the penetrable carrier substrate 204 and form a reinforced composite material. In either embodiment (i.e., where the penetrable carrier substrate 204 is a mesh material or a material with no holes/opening), the adhesive layer 206 may be discontinuous.
The adhesive used in the adhesive layer 206 may be a functional adhesive (switchable adhesive). For example, the adhesive may be a modified permanent or semi-permanent pressure sensitive adhesive (PSA) so that the diced wafer on a wafer tape (with separated dies) can be easily transferred to the penetrable carrier 250. By choosing an appropriate high-adhesion adhesive, the diced wafers can be made to transfer from the wafer tape to the penetrable carrier 250. Later, the pressure sensitive adhesive on the penetrable carrier 250 may be switched off to become a low tack, low adhesion pressure sensitive adhesive. With low adhesion, a die can be easily dispensed to another substrate as long as a pin can penetrate through the penetrable carrier 250 and overcome the residual adhesion force. Examples of functional adhesives include ultraviolet (UV) switchable or temperature switchable PSA. UV detackifiable pressure sensitive tape with a UV detackifiable adhesive is already widely used in the semiconductor industry for wafer grinding, dicing, etc.
The transfer of the wafer comprising the plurality of chips 208 to the penetrable carrier 250 can be accomplished by any known means, including tape-to-tape transfer of the entire wafer using UV or temperature switchable adhesives. In another preferred embodiment, instead of transferring the entire wafer of chips to the penetrable carrier 250, only predetermined portions of the plurality of chips 206 are transferred to the penetrable carrier 250. Thus, for example, only every other chip in each row and column of a wafer may be transferred. In this way, a desired space may be achieved between the chips on the penetrable carrier 250 before the penetrable carrier 250 is brought into contact with the strap lead web 302. In yet another preferred embodiment, a die testing/sorting machine may be use to test/sort the dies and place them onto the carrier one-by-one with a unique pitch. It is also possible that one can eliminate the process of transferring diced wafers to the new carrier simply by dicing the wafer directly on the pin penetrable carrier.
As described herein, a fiber-reinforced composite material comprising a mesh web may be used as the penetrable carrier substrate 204. In one example, a mesh is selected that has a unique mesh count allowing each individual chip to cover about 9 holes of the mesh web (i.e., the penetrable carrier substrate 204) in the penetrable carrier 250. The exact number of holes covered by each chip, the orientation of each chip on the penetrable carrier 250, or whether there is complete coverage of all the holes by the plurality of chips 208 is unimportant, but it is desirable that each chip cover at least one mesh hole so that the chip may be pushed through the hole using a pin, as described herein.
In step 104, which in one preferred embodiment as described herein is a chip orientation stage that may be optional, the orientation of the plurality of chips 208 is adjusted so that the contact pad side of each chip is exposed. Specifically, one or more transfers of the wafer to intermediate support(s) may be required in order to achieve the desired “pads up” or “pads down” orientation of the plurality of chips 208 prior to their transfer to the penetrable carrier 250.
After the plurality of chips 208 has been mounted on the penetrable carrier 250, the chip (i.e., electronic device) placement process 150 continues, as further detailed herein, where chips from the plurality of chips 208 are transferred from the penetrable carrier 250 to a strap lead web 302 and attached to a respective strap lead (i.e., the chips on the penetrable carrier 250 are transferred and each attached to a respective strap lead on a strap lead web). In one preferred embodiment, the chip placement process 150 begins with the penetrable carrier and strap lead (i.e., device) web alignment stage 106, during which chips from the plurality of chips 208 on the penetrable carrier 250 are aligned to and also brought into contact with a plurality of strap contacts 306 on the strap lead web 302, as seen in
In one preferred embodiment, because the pitch of the plurality of chips 208 is different than the pitch of the plurality of strap contacts 306, not all chips in the plurality of chips 208 will be transferred in a single step. In other words, when the spacing between the plurality of chips 208 does not match the spacing of the plurality of strap contacts 306, then only a subset of the plurality of chips 208 will be transferred to the plurality of strap contacts 306. In one preferred embodiment, the spacing of the plurality of strap contacts 306 is a whole number multiple of the spacing between the plurality of chips 208,
Also illustrated in
In another preferred embodiment, instead of simultaneously actuating all of the pins, which in the example are spaced at a fixed pitch, pins can selectively be actuated or deployed. In this case, the number of pins used as compared to the number of strap leads on the strap lead web is not a one-to-one relationship and can be a many-to-one (or one-to-many) relationship. Thus, chips can be selectively dispensed by selectively actuating respective pins. Similar to a player piano mechanism, wherein selective pins can be used to trigger the striking of a note, certain ones of the pins in the pin array 450 can be activated to pin selected chips to the strap lead web 302. In addition, rows of pins in the pin array 450 may be used to push chips onto the strap lead web 302. In this case, the pitch of the dispensed chips is determined by which of the pins in the array are activated.
In the penetrable carrier detachment stage 110, as illustrated in
During the pin array removal stage 112, as illustrated in
In one preferred embodiment, the adhesive spots 304 are cured before the plurality of pins 452 are withdrawn. In another preferred embodiment, a separate bonding and curing stage 114 is used to bond the subset of transferred chips 208b to the plurality of strap contacts 306 after the plurality of pins 452 has been removed.
With the transferred dies adhered to the strap lead web 302 by the adhesive spot (cured or uncured), withdrawal of the plurality of pins 452 completes one cycle of transferring the chips to the strap lead web 302, and the penetrable carrier 250 may now be repositioned to transfer additional chips from the subset of non-transferred chips 208a onto another plurality of strap leads. Thus, the process 100 may be repeated until all the chips of the plurality of chips 208 are transferred.
In another preferred embodiment, instead of applying the adhesive 206 onto/into the penetrable carrier substrate 204, the adhesive may be dispensed, or coated, onto the plurality of chips 208. The dies with adhesive are then laminated with the penetrable carrier substrate 204 (whether the substrate is a film, a mesh, etc. Similarly, before the die transfer to the strap/antenna substrate, the adhesive spot (ACP, NCP, etc.) can be applied onto the dies instead of being placed on the substrate. Regardless of how the adhesive spots are dispensed, it is preferred that the adhesive spot volume can be carefully controlled. Too little adhesive will give a weak bond strength, while too much adhesive may cause adhesive paste to be smeared onto the other, adjacent dies or to the substrate.
In one preferred embodiment, assuming wafers are transferred to the penetrable carrier without a change in pitch, multiple strap lead webs can be used, with each strap lead web being in parallel with each other (i.e., side by side). For example, each strap lead web only has a width of one column and corresponds to one column of chips in the wafer. In this way, multiple columns of chips can be dispensed at the same time.
Instead of using the ideas in this invention for bonding dies to strap leads or antennas, it is possible to use the method to transfer dies to a unique format for feeding Surface-Mount Technology (SMT) machines. SMT typically requires the components to be fed from a linear tape, a shuttle, or a waffle pack, etc. The machine that transfers dies from a wafer to an appropriate form to feed SMT can be slow and expensive. This invention can be used to prepare and transfer dies from a wafer to an appropriate form (on a tape, a shuttle, a waffle pack, etc.) for feeding the SMT.
It should be noted that the process described herein may be applied not only to the manufacture of RFID devices, but to other kinds of electronic devices, optoelectronic devices or display assemblies that require massive, high speed, and low cost attachment of components to printed circuit boards or flexible electronics webs.
The embodiments described above are exemplary embodiments of the present invention. Those skilled in the art may now make numerous uses of, and departures from, the above-described embodiments without departing from the inventive concepts disclosed herein. Accordingly, the present invention is to be defined solely by the scope of the following claims.
