No assignee for this patent application has been made.
News editors obtained the following quote from the background information supplied by the inventors: "The present invention relates to the field of handling electronic components that are normally processed on a wafer. After completion of the individual components on the wafer, the components are then diced. For this purpose, the wafer is mounted on a carrier material. The components or chips being diced are sawed on the carrier material whereas the carrier material itself is not sawed through. After sawing, the individual components are separated from one another on the carrier material by dice channels. The components must be lifted from the carrier material in order to be further processed. Specialized tools are used in the semiconductor industry for lifting the individual components or chips from the carrier material. Such ejection tools lift the chips using needles from the back side of the carrier material. A prior art tool of this type is shown in FIG. 1. In this case, the chip placed on the carrier material is lifted with needles rounded at their tips from the side that is attached to the carrier material. Generally, the carrier material is an adhesive carrier film. Lifting both the carrier material and the chip together loosens the adhesion of the carrier material at the edge of the chip. Residual adhesion remains between the carrier material and the chip. The chip is then removed by means of a vacuum gripper to be further processed. In this step the carrier material is usually not severed from the ejection tool.
"EP patent EP 0 565 781 B1 also shows an ejection tool for the semiconductor industry. With the aid of an ejector needle disposed in a fixed position the chip is lifted through the adhesive carrier film. In this process, the carrier film is not necessarily pierced by the conical needle. If it is pierced, only a small hole results, so that when further raising the needle the carrier film, due to the conical, tapered shape of the needle, is also further lifted.
"The problem that arises during the process of lifting the diced chips from the wafer composite is the risk that the chip will break or that the adjacent chips will be damaged. The drawback of the prior art in this regard is that either residual adhesion forces of the adhesive carrier film act on the chip while it is being removed by the take-up tool, generally a vacuum gripper, from the ejection tool, or that when the chip is first lifted by the needle of the ejection tool, too much pressure and tension is applied to the carrier material as the carrier material is also being lifted by the needle, and therefore to the chip being lifted and to the adjacent chips, whereby the chips break.
"Therefore, the object of the invention is to reduce the risk of chip breakage and thereby increase the yield of functioning chips. In particular for chips that are especially thin, that are made of a particularly brittle material or that lack a rectangular shape because they include, for example, monolithically integrated wave guide antennas, a method and a device are provided which enable damage-free lifting of the chip and which increase the yield of undamaged chips."
As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventor's summary information for this patent application: "An ejection device is provided for lifting a chip from a carrier material having at least one needle, wherein the needle includes at least one cutting edge. The advantage of the cutting edge is that when lifting the chip from the side adjacent the carrier material, the carrier material is cut through during lifting by the at least one needle. This prevents the carrier material from also being lifted during the lifting process and pressure from being exerted on the adjacent chips. To lift the chip the needle is pressed against the carrier material and the overlying chip. Here, the carrier material is lifted slightly only initially until the tip of the needle lightly pierces the carrier material, as the needle is further raised the carrier material is cut through due to the cutting edge along the front portion of the needle, and is as a result no longer lifted.
"The penetration resistance of the needle is reduced as a result of the cutting edge, and the carrier material is cut through as a result of the pressure of the cutting edge of the needle against the carrier material during the lifting process. Thus, the mechanical forces acting on the chips during the lifting process are significantly reduced. In addition, there are no residual adhesion forces of the carrier material acting on the chip when the latter after being lifting is removed from the ejection tool by a vacuum gripper to be further processed.
"Here, a needle is seen to be a rod-shaped device wherein it is the front portion of the needle that is involved in the lifting process. The foremost end of the needle is designated the needle tip. During the lifting process, it is the needle tip that first comes into contact with the carrier material and with the chip and supports the chip during lifting.
"The end opposite the needle tip is designated the needle end.
"It was seen as advantageous that the grinding of the front portion of the needle has at least one cutting edge that cuts through the carrier material during the lifting process. The needle is sharpened so as to form a sharp edge which cuts through, that is severs, the carrier material. The cutting edge is preferably formed as a lateral edge along the front portion of the needle. In this configuration the front portion of the needle can be shaped as a knife with a sharp lateral edge or also two opposing sharp lateral edges. The cutting edge is ground to form a wedge-shaped lateral edge. Preferably the cutting edges are prepared so that the needles also gradually taper in the direction of the needle tip.
"Thus, according to the invention, to lift a chip from a carrier material a needle is used which includes at least one cutting edge for cutting through the carrier material.
"A carrier material in the form of an adhesive carrier film is preferably used, on which the wafer is placed for the chips to be diced and which adheres to the former. This can be a plastic film, for example.
"The chip to be lifted is, for example, a semiconductor chip fabricated on a semiconductor wafer. The embodiment of the ejection device according to the invention and the method according to the invention are advantageous in particular for chips for MMICs that are produced from III/V semiconductor material, for example, chips produced from GaAs or InP thinned to 20 on down to 100 .mu.m.
"Another embodiment of the extraction device for lifting a chip from a carrier material includes at least one needle, wherein the diameter of the needle is smaller than or equal to 0.25 mm. This choice of needle diameter ensures that the penetration resistance of the needle in the carrier material during the lifting process is minimal. Based on this diameter it is also possible for the needle to be ground on the front section of the needle. In particular, it is possible for the needle to have at least one cutting edge.
"In a further embodiment the needle of the ejection device includes three cutting edges for cutting through the carrier material. By using three cutting edges the needle cuts through, that is, severs the carrier material as the chip is lifted. Preferably, the cutting edges are prepared such that the needle also gradually tapers in the direction of the needle tip.
"Thus, to lift a chip from a carrier material, a needle is used that has three cutting edges for cutting through the carrier material.
"The cutting edges are formed along the front portion of the needle in such a way that three sharp lateral edges, for example pyramid-shaped, extend along the front portion of the needle. The former cut through the carrier material along the lifting path as the needle is raised. In this way the chip is lifted from the carrier material and detached from the chip composite.
"In a further embodiment the ejection device comprises a needle holder with holes for receiving at least one needle, in addition the ejection device includes a needle head and a compression spring, wherein the needle head and the needle holder can be assembled so that when assembled, the needle head and the needle holder via the compression spring are moveable relative to one another. The advantage of this is that during operation, the ejection device functions so that the needle tips are recessed in the ejection device so that the tips remain protected. During operation the carrier material with the wafer travels over the needle head and cannot damage the recessed tips. Not until the chip being ejected is positioned over the needle head are the needles forced in the direction of the needle head and the needle tips come into contact with the overlying carrier material and the chip mounted thereon.
"Designated as compression springs are components which yield under stress and upon release return to their original shape, are therefore elastically resetting.
"As a further embodiment of the ejection device, the ejection device can be fitted with needles based on the area of the chip to be lifted, wherein the density of the needles is at least three needles per 1 mm.sup.2 of chip area. Thus, the needle density of the ejection device in this embodiment is selected so that at least one needle is positioned on 0.33 mm.sup.2 of chip area. The advantage of this is that the problem of concentrated forces acting on the chip during lifting is distributed to multiple needles. Such pressure distribution reduces the flexural moment on the chip, since multiple points on the chip are affected simultaneously. As a result the chip breaks less easily during the lifting process. Since according to the invention the selected diameter of the needles used in a preferred embodiment is particularly small, the needle density per chip area can be increased, as opposed to the prior art which operates with needle diameters of 0.5 to 0.7 mm. Additional needle densities used according to the invention are preferably 4 needles per 1 mm.sup.2 of chip area, that is, at least one needle is positioned on 0.25 mm.sup.2, and at least 5 needles per 1 mm.sup.2 of chip area, that is, at least 1 needle is positioned on 0.2 mm.sup.2 of chip area. Thus, the needle density selected according to the invention falls preferably between 3 to 5 needles per 1 mm.sup.2 of chip area.
"In a further embodiment the at least one needle is fixed in the needle holder such that the at least one needle is fixed in the needle holder by means of a hotmelt adhesive. Thus, the needle is fixed in a rigid medium in the needle holder. This means that the at least one needle is introduced into a liquid medium in the needle holder during production of the ejection device, or the liquid medium is applied to the needle in the needle holder and in the subsequent process as the medium solidifies or cures, the needles become fixed in the needle holder. The advantage of such fixing is that when fixing the needle in the ejection device no mechanical forces act on the needle which lead to a deformation of the needle, as is the case in the prior art. In the prior art the needle is fixed with an allen screw, which can cause the needles to bend or shift.
"A particularly suitable medium for fixing the needles is a hotmelt adhesive which by changing temperature changes from a solid to a liquid state or conversely, from a liquid to a solid state. It is a solid at room temperature. It is applied in melted form and subsequently adheres to the respective surface when cooled again to a temperature below melting point.
"The method for fixing the needles in an ejection device for lifting a chip from a carrier material includes the following steps: inserting the at least one needle in a needle holder of the ejection device fixing the needles, whereby the ends of the needles are fixed in the needle holder by means of an adhesive as a result of the adhesive solidifying or curing.
"The advantage of the method is that the needles in the ejection device are mounted in such a way that they are not tensed or warped. This is particularly important when multiple needles must be inserted in order, for example, to cover a larger chip area, and for that purpose the needle tips must be aligned as precisely as possible in a single plane.
"Adhesives are non-metallic materials that bind substrates by means of adhesion or cohesion. Hotmelt adhesives have proven to be especially suitable for fixing needles, particularly because the former are easily removable. A hotmelt adhesive that can be removed with a dissolvent is especially suitable. A hotmelt adhesive is applied in liquid form, then adheres to the respective surface when cooled again to a temperature below melting point. Particularly suitable are hotmelt adhesives containing wax or hotmelt adhesive consisting of wax.
"The method for fixing at least one needle in a needle holder (8) of an ejection device for lifting a chip from a carrier material further includes the following steps that precede the fixing of the needles, introducing the at least one needle into the at least one hole of the needle holder, wherein one needle each is introduced into one hole each of the needle holder aligning the plane of the needle tips, wherein the needles guided loosely in the holes of the ejection device are aligned with their needle tips on a level plate as a result of their own weight.
"This method step ensures that the needles are seated in the correct position prior to fixing and the plane of the needle tips is set.
"In a further embodiment of the method the adhesive is a hotmelt adhesive, the latter being applied to the needle ends in the form of a granulate, and in a further step the granulate is melted and solidified in a further step.
"The method claimed herein ensures that the needles are fixed to the tool in such a way that when fixed they do not become misaligned.
"In a further embodiment of the method for fixing at least one needle in a needle holder of an ejection device for lifting a chip from a carrier material, a still further method step is implemented. In this step, once the adhesive is applied and before the adhesive solidifies, the needle holder is moved downward a short distance, for example, approximately 0.5 mm in the direction of the flat plate on which the needle tips are aligned in order prior to solidification of the adhesive to ensure once again an alignment of the needle tips in a plane. Such movement of the needle holder in the direction of the flat plate corrects for any slight upward movement of the one or other needle caused by dispersal of the adhesive and forces all the needle tips again in the direction of the flat plate.
"A mounting device is used for mounting the ejection device. The mounting device according to the invention for inserting and fixing at least one needle in an ejection device includes a plate for aligning the plane of the needle tips and a removable attachment and a connecting piece, wherein the plate (12) can be connected to the removable attachment (13) via the connecting piece (14) in such a way that the removable attachment (13) can be attached to the needle holder, needle head and compression spring via the connecting piece (14), such that after the fixing process the needles (4) are recess mounted in the ejection device. The advantage of this feature is that once the needles are mounted they are situated somewhat recessed in the ejection tool and the needle tips are protected as a result. Only when the ejection tool is used to lift the chip are the needles forced out of the ejection tool.
"According to a further embodiment of the mounting device, the removable attachment has a recess and the removable attachment together with the recess can be mounted over the needle holder of the ejection device in such a way that the recess functions to introduce the fixing material onto the needle ends in the needle holder
"A method according to the invention for lifting a chip from a chip composite mounted on a carrier material comprises the following steps:--lifting the chip with the aid of at least one needle, wherein the chip is lifted from the side of the chip facing toward the carrier material, wherein lifting occurs in that the at least one needle includes at least one cutting edge and the at least one needle through the carrier material lifts the chip and during lifting the carrier material is cut through by the cutting edge.
"According to a further embodiment of the method for lifting a chip from a carrier material, the at least one needle has a diameter that is smaller or equal to 0.25 mm. The advantage of this is that needle severs the carrier material during lifting. In particular, including a cutting edge on the front end of the needles ensures that the carrier film on which the chips rest is lifted barely or not at all during the lifting process. As a further advantage, because there are virtually no expansion stresses acting on the foil, the adjacent chips that are momentarily not directly involved in the lifting process are not damaged, which normally occurs as a result of the shifting of the chip when the carrier film is lifted during the removal process. By lifting the carrier film the edges of the adjacent chips would slide onto one another and become damaged as a result. This is prevented by the present invention. Moreover, there are no residual adhesion forces of the carrier film acting on the chip when the latter is lifted with a vacuum gripper from the side opposite the needle to be further processed.
"According to a further embodiment of the method for lifting a chip from a carrier material the following steps are implemented:--lifting the chip using an ejection device having at least one needle, wherein the chip is lifted from the side of the chip that faces toward the carrier material, wherein the at least one needle through the carrier material lifts the chip, characterized in that the ejection device is fitted with needles based on the area of the chip to be removed, specifically, with a needle density of at least one needle per 0.33 mm.sup.2 of chip area.
"This ensures that a sufficient number of needle tips are positioned per chip area in order to distribute the mechanical forces uniformly across the chip area, and so that too great a pressure does not build up locally at one point on the chip. In this regard, it has been found that per 1 mm.sup.2 of chip area a distribution of at least three, at least four or at least five needles across this chip area ensures an optimum pressure distribution.
"An ejection device according to the invention is especially suited for fabrication machines used to lift a chip from a carrier material and to take up the chip for further processing, wherein the chip is lifted from the carrier material by an ejection device according to the invention, and with a take-up tool the chip is removed from the ejection device. The ejection device ensures that the chip is detached from the chip composite and is presented so that a take-up tool is able to take the chip without damage to itself or to the adjacent chips. Fabrication machines of this type in the semiconductor industry then deposit the chip, for example, in a packaging. Semiconductor fabrication machines of this type that have an ejection device and a take-up device are, for example, die bonders. The take-up tool is generally a vacuum gripper that removes the chip from the needle from the side opposite the needle of the ejection device. It is advantageous in the case of this highly automated process if the chip is completely separated from the adhesive carrier film and no residual adhesive forces are affecting the chip which could strain the chip as it is being taken up. This is ensured with the ejection device according to the invention by cutting through the carrier film during the lifting process.
BRIEF DESCRIPTION OF THE DRAWINGS
"Further advantages and features of the present invention are described below with reference to FIGS. 1 through 7.
"FIG. 1: shows an ejection device according to the prior art
"FIG. 2: shows an ejection device according to the invention during lifting of a chip from a chip composite
"FIG. 3: shows a needle according to the invention with a corresponding grinding at the front end of the needle
"FIGS. 4a and 4b: show a specific embodiment of the ejection device with needles, needle holder, compression spring and needle head from two different perspectives
"FIG. 5: shows schematically an embodiment of the mounting device
"FIG. 6: shows an ejection device in which the needles are extended
"FIG. 7: shows a needle with a triangular cut on the front portion of the needle"
For additional information on this patent application, see: Rie le,
Keywords for this news article include: Patents, Electronics, Semiconductor.
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