The invention relates to the fabrication of a semiconductor chip. More particularly, the invention relates to a device for assembling the semiconductor chip and, further, for the assembly of a flip chip. Background

A flip chip defines a system for interconnecting semiconductor devices such as IC chips and MEMS systems to external systems having solder bumps deposited on chip pads.

The general process for fabricating the chips includes providing ICs on a wafer to which a solder ball is deposited. The chips are then flipped so as to face the solder balls towards the external system and then re-melt the solder balls to complete the electrical connection.

This presents two distinct problems. Firstly, to efficiently flip large numbers of chips and, secondly, to apply sufficient heat to the chip so as to re-melt the solder balls.

Summary of Invention In a first aspect the invention provides a system for mounting a flip chip, comprising: at least one flipper arm, having an engagement end; said flipper arm arranged to rotate in a vertical plane; said engagement end arranged to engage a chip and, on engagement, rotate 180°.

Accordingly, by having rotatable flipper arms arranged to separately engage chips on the wafer, the system provides a rapid and controllable arrangement in order to position, align and inspect the chips prior to re-melting of the solder balls.

In a second aspect the invention provides a system for bonding a chip to a substrate, comprising: a heat bond head assembly, said heat bond head assembly including at least one bond head; the bond head arranged to contact the chip positioned to the substrate, and apply heat to said chip; wherein the bond head is arranged to apply heat to melt solder balls intermediate the chip and substrate.

In a third aspect the invention provides a method for bonding a chip to a substrate, comprising the steps of: placing a chip on a substrate, having solder balls intermediate the chip and substrate; applying heat to the chip from a bond head; melting solder balls intermediate the chip and substrate.

Whereby pickers of the prior art are used to reheat the solder balls, the present invention provides a heat bond head for directing heat directly to the chips whilst on the substrate boat, which eliminates the problems associated with heated pickers to achieve the re- melt. The typical means of reheating the solder balls involves transferring the chips from the wafer to the substrate using heated pickers. Thus, the picker engages the chip then traversing the distance from one station to the next applies heat to the chip in order to re-melt the solder ball for engagement with the substrate. Whilst this may be seen as an efficient means of applying the heat by combining both delivery and heat application, in fact this introduces significant problems. At the time of engaging the chip the picker must be relatively cool and then rapidly heat up on delivering the chip across a relatively short distance. On depositing the chip the picker then must dissipate heat so as to be at a reasonable temperature before engaging the next chip. Regardless of any benefits of combining these actions, in fact this leads to a bottleneck as heat transfer to dissipate the heat involves a finite amount of time which results in the controlling perimeter during delivery. Whereas a conventional picker can travel quite rapidly, a picker for a flip chip travels much slower because of the heat dissipation time on its return journey.

Brief Description of Drawings

It will be convenient to further describe the present invention with respect to the accompanying drawings that illustrate possible arrangements of the invention. Other arrangements of the invention are possible and consequently, the particularity of the accompanying drawings is not to be understood as superseding the generality of the preceding description of the invention. Figure 1 is a plan view of a flip chip mounting device according to one embodiment of the present invention;

Figure 2 is a plan view of the heat bonding station according to a further embodiment of the present invention;

Figure 3 is an elevation schematic view of a flipping system according to a further embodiment of the present invention, and; Figure 4 is an elevation schematic view of a heat bonding station according to a further embodiment of the present invention.

Detailed Description Figure 1 shows a flip chip mounting device 3 according to one embodiment of the present invention.

In this particular embodiment, the device includes a loading station 5 arranged to load wafers 10 and substrates 80 into the respective flipping station 9 and heat bonding station 7. The process for the flipping station 9 begins with the wafer 10 mounted to the wafer loader 15. The wafer gripper 20 travelling along the gripper rail 25 engages the wafer and pulls it onto the working table 35.

The flipping station 9 in addition to the working table 35 includes a pair of flippers 40 A, 40B and an ejector 45. Once located on the working table 35, the working table then moves along perpendicular principle axes so as to position each chip above the ejector 45, which is arranged to press the chip upwards for engagement by an engagement end of one of the flippers 40A, 40B. As described with reference to Figure 5, the flipper 40A, B then rotates 180° so that the chip is inverted, or is projected the chip upwards, and so "flipping" the chip. Once flipped, the die bond picker 60A, 60B travelling along the picker rail 70A, 70B engages the chip, as the flipper 40A, 40B simultaneously releases it. The picker then dips the chip into the flux table 55 for transferring flux to the chip then passes the chip over an upward directed orientation vision 50A, 50B to confirm the alignment of the chip on the picker.

The chip is subsequently placed on the substrate 55A within the substrate boat 57A, B. Mounted with the picker 60A, B is a further alignment vision 65A, B for inspecting downwards to assist with the alignment of the chip on the substrate as it is placed. Once the final alignment inspection has been passed, the substrate is then delivered to the output magazine 80 for packaging. For this embodiment, the means by which the solder balls are melted may be through using heated pickers, according to the prior art. Alternatively, or in combination, the substrate boat 57A,B may include a heating unit for applying heat to the substrate and chip, and thus melt the solder balls once placed. The heating unit may include an induction coil within the substrate boat, or a thermo-electric device such as a peltier unit.

Figure 2 shows an alternative heat bonding station 90. As can be seen, it uses the same arrangement of a substrate 100 located within the substrate boat 57. The substrate boat 57 includes rails 95 which are selectively lowerable to provide access to the substrate by the pickers 60 and once the chip has been placed on the substrate, the rails 95 raise once again to ensure the orientation of the substrate 100 within the boat 57.

Where the embodiment of Figure 2 varies from the embodiment of Figure 1 is the inclusion of a heat bond head assembly 105. The heat bonding station shown in Figure 2 may be used in combination with the flipping station shown in Figure 1. Alternatively, the heat bonding station of Figure 2 may be used with a different device. The heat bond head assembly 105 includes two bond heads 110 all mounted on a rail 115 so as to position the bond heads over the substrate, in particular directly above the chip and the substrate. The heat bond head assembly 105 is arranged to apply a combination of heat and compression to the chip and substrate so as to ensure the solder ball is effectively re-melted and engaged with the substrate. This is demonstrated at Figure 4 whereby the substrate boat 57 includes the substrate 100 and upon which a plurality of chips 175 are engaged with the substrate 100 via the solder balls 180. The heat bond head assembly 165 includes at least one and perhaps several bond heads 170 which are arranged to be lowered by the heat bond head assembly 165 so as to be in contact with the chip 185. The bond head 170 then applies heat to the chip and consequently the solder balls 180 so as to re-melt the solder balls to engage with the substrate 100. In a further embodiment, in addition to the application of heat, the bond head 170 may also apply a compressive force so as to marginally deform the melted solder balls to ensure a viable connection with the substrate. The bond head may apply heat through a range of different means, including induction and thermo-electric devices. Alternatively, the bond head may melt the solder balls using an ultrasonic device. It will be appreciated that a heated substrate boat as described earlier may be used in combination with the heat bond head assembly.

In a still further embodiment, while the substrate boat 57 engages the substrate through a vacuum seal, in this embodiment the vacuum seal may be significantly higher than is normally required so as to not only engage the substrate to the substrate boat 57 but to also ensure the substrate 100 is flattened through the application of the vacuum. This flattening pressure then ensures the solder balls engage the substrate evenly across the substrate without a gap or in complete connection made through bowing of the substrate. The skilled person will understand that the vacuum required to hold the substrate in place will be at a certain pressure and that the vacuum required to flatten the substrate will be significantly higher. Further still, as the invention applies to a range of substrates and chips for the flip chip process, such pressures will vary depending upon the application to the substrates size but nevertheless will be available and understood by the skilled person.

Figure 3 shows an embodiment of the flipping station 120 whereby flippers 40 A, 40B are arranged to engage chips 140 on the wafer 30.

The flippers 40 A, 40B operate together with the working table 162, which moves 160 relative to the flippers 40A,B. The moving working table 162 moves 160 the wafer 30 so as to position the chip 140 above the ejector 145. The flipper 40A,B includes flipping arms 125A,B which rotate in the vertical plane in an alternating process to engage with chips at the engagement point 157. The ejector lifts 145 the chip 150 so as to engage with an arm 125 A of the flipper. The arm 125B then rotates 130 about an axle 135 so as to invert, or flip, the chip 155 and present the chip for engagement by the picker (not shown). Thus, as the working table is moved to present chips to be engaged, the flipping arms alternate to engage the chip and deliver to their respective pickers.