Field Of Invention

The present invention relates generally to cooling and lubrication systems. In particular, the invention relates to cooling and lubrication systems using wave- charged liquid.

Background

Integrated circuit (IC) chips are fabricated with multiple IC chips being typically arranged on a single supporting substrate. In a conventional IC packaging process, silicon dies are initially bonded on the paddles of a lead frame by die bonding, wire bonding apparatus or flip chip mounting, and subsequently encapsulated in a molding compound to obtain a single substrate and eventually singulated to obtain individually separated IC packages therefrom.

Generally, the IC packages are separated using a saw, a dicing saw or the like cutting devices. Typically, one or more special water nozzles are designed for directing water towards a saw for cooling and lubrication thereof during the dicing process.

An expanding market for Quad Flat No-Leads (QFN) packages has consequently increased the demand for high throughput singulation of smaller QFN packages. However, conventional singulation methods utilising conventional cooling and lubrication methods are now facing problems in obtaining quality cuts. Since a saw, for example a dicing saw, rotates at a very high speed, an air curtain or an air layer is formed around the rotating saw. This air curtain prevents cooling water from entering into the cutting zone to effectively cool and lubricate the saw.

Additionally, cutting of soft material, for example copper, without suitable cooling and lubrication conditions will result in chips being lodged in the saw which further elevates the temperature at the cutting zone even higher. The product of this temperature elevation at the cutting zone is the visually evident big smearing and burring after dicing.

Hence, this clearly affirms a need for an improved cooling and lubrication system for singulating or dicing of semiconductor packages and semiconductor substrates.

Summary In accordance with a first aspect of the invention, there is disclosed a cooling and lubrication system comprising: a chamber; a wave generator coupled to the chamber for generating and transmitting ultrasonic waves to liquid supplied through the chamber for obtaining wave-charged liquid therefrom; and a nozzle being in fluid communication with and for receiving the wave- charged liquid from the chamber, the nozzle for directing the wave-charged liquid towards a saw, whereby the saw is substantially enveloped by an air curtain when rotating, the air curtain being substantially liquid deflecting, wherein the wave-charged liquid is for penetrating the air curtain to thereby contact the rotating saw for at least one of cooling and lubrication thereof.

In accordance with a second aspect of the invention, there is disclosed a cooling and lubrication method comprising the steps of: generating and transmitting ultrasonic waves by a wave generator to liquid supplied through a chamber for obtaining wave-charged liquid therefrom; and positioning a nozzle for directing the wave-charged liquid towards a saw, the nozzle being in fluid communication with and for receiving the wave-charged liquid from the chamber, whereby the saw is substantially enveloped by an air curtain when rotating, the air curtain being substantially liquid deflecting, wherein the wave-charged liquid is for penetrating the air curtain to thereby contact the rotating saw for at least one of cooling and lubrication thereof.

Brief Description Of The Drawings

Embodiments of the invention are described hereinafter with reference to the following drawings, in which:

FIG. 1 shows a front sectional elevation of a cooling and lubrication system according to an embodiment of the invention;

FIG. 2 shows a perspective view of the cooling and lubrication system of FIG. 1 when incorporated with a semiconductor substrate singulation system; and

FIG. 3 shows a side sectional elevation of the cooling and lubrication system according to view 'A' of FIG. 2.

Detailed Description A cooling and lubrication system is described hereinafter for addressing the foregoing problems.

An embodiment of the invention, a cooling and lubrication system 20 is described with reference to FIG. 1 , which shows a front sectional elevation of the cooling and lubrication system 20, and FIG. 2, which shows a perspective view of the cooling and lubrication system 20.

As shown in FIG. 1 and FIG. 2, the cooling and lubrication system 20 comprises a wave generator 22, a nozzle 24 and a chamber 26. The chamber 26 is formed within a housing 28 and is in fluid communication with the nozzle 24. The housing 28 and the nozzle 24 are preferably formed as an integral structure. The liquid 30 is at least one of a coolant and a lubricant. Preferably, the liquid 30 is de-ionised (DI) water.

The cooling and lubrication system 20 further comprises a conduit 32 being in fluid communication with the chamber 26. The conduit 32 is formed in a tube 34 coupled to the housing 28. The conduit 32 is for carrying liquid 30 therethrough and directing the liquid 30 into the chamber 26.

The wave generator 22 comprises a wave transducer 36 and a wave oscillator 38 electrically communicating with the wave transducer 36. The wave transducer 36 is coupled to the housing 28 with the chamber 26 being ultrasonic wave transparent. The wave oscillator 38 is for generating ultrasonic electrical signals for transmission to the wave transducer 36. The wave transducer 36 is for transducing the ultrasonic electrical signals received from the wave oscillator 38 into ultrasonic waves. Preferably, an impedance converter 39 electrically interfaces the wave transducer 36 and the wave oscillator 38 for impedance matching therebetween.

Therefore, when liquid 30 is supplied through the chamber 26, the ultrasonic wave generated by the wave transducer 36 resonates and converts the liquid 30 into wave- charged liquid 40. The wave-charged liquid 40 is then discharged through the nozzle 24 with the nozzle determining the discharge direction thereof.

The cooling and lubrication system 20 is preferably used in conjunction with one of a singulation system and a dicing system.

In an example, a saw jig with a rubber pad support (both not shown) is used for supporting a work-piece 42. The work-piece 42 is one of a semiconductor package and a semiconductor substrate. For example, the work-piece 42 consists of quad-flat no-lead (QFN) packages. Vacuum generated through vacuum holes formed in the rubber pad further secures the work-piece 42 to the saw jig both during and after sawing of the work-piece 42.

With reference to FIGS. 1, 2 and 3, a conventional saw 44 is used for sawing the semiconductor substrate 42. The saw 44 is preferably substantially planar, disc¬ shaped and has a periphery 50. The saw 44 is coupled to a spindle 46 which transmits rotational displacement thereto. The spindle 46, which is electrically actuated, is housed within a spindle housing 47. During a sawing process, the saw 44 rotates at a substantially high rotational speed. This high rotational speed results in an air curtain, also typically known as an air layer, being formed around and substantially enveloping the saw 44.

This air curtain is liquid deflecting and is substantially effective in forming a barrier between the saw 44 and any liquid 30, for example coolants and lubricants, directed thereat. However, converting the liquid 30 into wave-charged liquid 40 enables the wave-charged liquid 40 to effectively penetrate the air curtain for delivery to the saw 44. This enables the wave-charged liquid 40 to contact the rotating saw 44 for at least one of cooling and lubrication thereof.

The work-piece 42 has a surface 52 and a cut path 54 along which the saw 44 traverses and interacts with the work-piece 42 for sawing thereof. The saw 44 rotates about an axis which is substantially parallel to the surface 52 of the work-piece 42. Preferably, the nozzle 24 is positioned for directing the wave-charge liquid 40 towards a portion of the periphery 50 of the saw 44 proximal to an entry point 56 whereat each portion of the periphery 50 enters and cut into the surface 52 of the work-piece 42. The cut path 54 extends from the entry point 56 into the work-piece 42. Alternatively, the wave-charged liquid 40 is directed at the entry point 56 on the surface 52 of the work-piece 42.

Once the wave-charged liquid 40 contacts a portion of the periphery 50 of the saw 44, the wave charged liquid 40 is redirected and guided towards the surface 52, and more specifically, the cut path 54 of the work-piece 42. As heat generated from sawing of the work-piece 42 is concentrated around the cut path 54, having the wave-charged liquid 40 directed thereat effectively lubricates and cools both the saw 44 and the work-piece 42 to produce high quality cutting via one of singulation and dicing.

Additionally, the wave-charged liquid 40 also facilitates flushing and cleaning of both the work-piece 42 and the saw 44 as a by-process.

The cooling and lubrication system 20 is also implementable in a multi-saw singulation system wherein more than one saw 44 is attached to the spindle 46, for example, a gang-saw. For the multi-saw singulation system, the nozzle is preferably shaped and dimensioned to enable effective delivery of wave-charged liquid 40 to each of the more than one saw 44 and the cut path 54 corresponding thereto. Alternatively, multiple nozzles 24 extend from a common chamber 36 or from

respective chambers 36 for effectively delivering the wave-charged liquid 40 to the more than one saw 44.

In the foregoing manner, a cooling and lubrication system is described according to one embodiment of the invention for addressing the foregoing disadvantages of conventional cooling methods and systems. Although only one embodiment of the invention is disclosed, it will be apparent to one skilled in the art in view of this disclosure that numerous changes and/or modification can be made without departing from the scope and spirit of the invention.