Abstract:
A method of singulating semiconductor devices applies a blade to a molded strip that includes the semiconductor device. The blade generates a kerf at a contact point between the blade and the molded strip. The kerf is filled with a plurality of particles. The kerf separates the semiconductor device from the molded strip. The method cools the blade by using a synthetic lubricant. The method lubricates the blade by using the synthetic lubricant. The method rinses the kerf by using the synthetic lubricant. Rinsing the kerf removes a substantial quantity of the particles from the kerf. A system singulates semiconductor devices from a molded strip by using a blade, a temperature control device, and a synthetic lubricant. The blade singulates the semiconductor device from the molded strip. The temperature control device applies the synthetic lubricant to the blade. The synthetic lubricant cools, lubricates, or rinses the blade, or a combination thereof, during a singulation process.

Description:
RELATED APPLICATIONS 
   The present application claims priority to U.S. Provisional Patent Application 60/792,093, filed on Apr. 13, 2006, and entitled “Method and Apparatus for High Speed Singulation” to the same inventors under U.S.C. section 119(e). This application incorporates U.S. Provisional Patent Application 60/792,093, filed on Apr. 13, 2006, and entitled “Method and Apparatus for High Speed Singulation” to the same inventor by reference in its entirety. 

   FIELD OF THE INVENTION 
   The present invention is related to the field of semiconductor device manufacturing. More specifically, the present invention relates to high speed singulation for semiconductor devices. 
   BACKGROUND 
   The manufacture of semiconductor integrated circuits has become a competitive, high volume commodity business. As such, controlling the cost of each completed circuit improves the commercial effectiveness of that circuit. For the semiconductor manufacturing industry, the time necessary to complete each manufacturing step has a direct relationship and effect on the cost of that circuit. One time-consuming phase during the fabrication of semiconductor devices is singulation. Singulation is a process for dicing a sheet of fabricated semiconductor die and/or packages into individual units. Semiconductor dice are typically mass produced on a wafer and good dice are mounted on a leadframe. The leadframes are also typically mass produced in large batches by the sheet. Depending on the manufacturing process, the sheet of leadframes can have an adhesive (dicing) tape applied to one side of the sheet before an encapsulation is applied to the dice mounted on the leadframes. The encapsulation is typically performed by molding a plastic resin to the sheet of dice and leadframes. In these cases, the dicing tape provides a lower support structure for the formation of the plastic molding during encapsulation. The encapsulation is commonly referred to as a semiconductor package. 
   A singulation process separates each package from the molded sheet. The molded sheet is typically divided into molded strips for singulation. There are various techniques currently being practiced for singulation. One technique involves punching, while another technique involves sawing the molded strip to separate the packages from the molded strip. Two particular drawbacks related to sawing the molded strip are (1) lengthy singulation times and (2) defects in the singulated product. Both drawbacks are related to the heat generated by the singulation blade. The saw blade cuts the resin and can cut the lead frame into a plurality of particles. While cutting, the blade forms a well-known trench-like kerf. The kerf can fill with particles which can bind between the blade and a wall of the kerf. The particles can damage the wall of the kerf leading to failures or reliability problems. 
   In a conventional process, the singulation blade is generally operated at a rotational (spindle) speed of 20,000 rotations per minute (RPM), and a table speed of two inches per second (IPS). These speeds are typical of a conventional “Disco” type singulation machine. As is commonly understood in the art, the table speed measures the (linear) speed of the blade moving along a molded strip during singulation of the molded strip, whereas the spindle speed approximates the rotational speed of the blade (about its axis), as the blade cuts through the molded strip. 
   The relatively slow conventional speeds are used in the art to reduce blade overheating, to preserve blade life, and to reduce the number of defects in the singulated product. As mentioned above, speeding up the singulation process is beneficial to improve throughput and thereby reduce costs associated with semiconductor manufacturing. While increasing the rotational speed of the blade can promote faster singulation, there are significant tradeoffs in a conventional singulation process. Higher blade speeds increase blade temperature, which results in lower cutting efficiency, higher blade wear, and more singulation defects. 
   To cool the blade, certain conventional singulation processes use deionized (DI) water. However, simple deionized water does not operate adequately to (1) cool the blade, (2) lubricate the blade, and (3) remove the buildup of particles on and around the blade and in the kerf during singulation, and particularly at higher RPM and/or lateral (IPS) blade movement. Simple deionized water has certain properties that inhibit proper service as a lubricant and coolant. One such property is the high surface tension of water, which causes the water to form high tension beads. The high tension beads do not distribute well over large surface areas, and do not penetrate into small spaces such as the kerf. Hence, the high tension beads do not adequately cool and lubricate high speed singulation blades, and do not properly remove the buildup of particles, which obstruct the blade during singulation. These obstructions lead to higher friction between the blade and the kerf, and the higher friction further causes high power consumption by the electric motor and other components of the blade. Thus, there is a need to accelerate the singulation process without negatively affecting the quality or reliability of the singulated product, or the longevity of useful blade life. 
   SUMMARY OF THE INVENTION 
   Some embodiments of the invention disclose a method of singulation for a semiconductor device. The method applies a blade to a molded strip that includes the semiconductor device. The blade generates a kerf at a contact point between the blade and the molded strip. The kerf has a plurality of particles cut by the blade. The kerf separates the semiconductor dice from each other. The method cools the blade by using a synthetic lubricant. The method lubricates the blade by using the synthetic lubricant or a combination of DI water and the synthetic lubricant. Hereafter, synthetic lubricant is meant to include the synthetic lubricant (and/or coolant) and a combination thereof with water. The method rinses the kerf by using the synthetic lubricant. Rinsing the kerf removes a substantial quantity of the particles from the kerf. 
   Preferably, the blade moves at a high rate of speed, such as, for instance, at a spindle speed of approximately 30,000 to 50,000 rotations per minute, and/or at a table speed of approximately 4-10 inches per minute. By lubricating the blade, the method substantially reduces the coefficient of friction between the blade and the kerf. The method typically cools the blade by directing the synthetic lubricant toward the blade, such that the temperature of the blade is substantially reduced. Moreover, the power consumed from the blade&#39;s operation is substantially reduced, such as, for instance, from 3.5 Amps to about 1.9 Amps, in some embodiments. 
   Rinsing the kerf typically comprises injecting the synthetic lubricant into the kerf. 
   For certain embodiments, the semiconductor device includes a die and/or leadframe. The molded strip of various embodiments includes a plurality of semiconductor packages. Often, the molded strip further has a dicing tape attached to a side of the molded strip. 
   Some embodiments of the invention provide a system for singulation of a semiconductor device. The system comprises a molded strip, a blade, a temperature control device, and a synthetic lubricant. The molded strip has a plurality of semiconductor devices. The blade is for singulating the semiconductor device from the molded strip. When the blade contacts the molded strip, the blade generates a kerf. The kerf has a plurality of particles. The temperature control device is configured to apply the synthetic lubricant to the blade. The synthetic lubricant cools the blade and lubricates the blade during a singulation process. 
   As mentioned above, the blade moves and/or rotates at a high rate of speed. The synthetic lubricant often substantially reduces the coefficient of friction between the blade and the kerf and/or substantially reduces the temperature of the blade. Moreover, the blade consumes less power. In some instances, the power consumption is about 1.9 Amps. The temperature control device of some embodiments further comprises a nozzle for directing the synthetic lubricant toward the blade. The nozzle of some embodiments injects the synthetic lubricant into the kerf. In these cases, the synthetic lubricant typically enters the kerf and substantially removes the particles from the kerf. 
   Some systems further include a dicing tape. The semiconductor devices of these systems are typically attached to the dicing tape. The semiconductor device of some embodiments comprises a die and/or leadframe and the molded strip often has one or more semiconductor packages thereon. These semiconductor packages typically include a leadframe, a semiconductor die coupled to the lead frame, and a capsule enclosing the semiconductor die. The leadframe of some embodiments comprises an alloy. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features of the invention are set forth in the appended claims. However, for purpose of explanation, several embodiments of the invention are set forth in the following figures. 
       FIG. 1  is an illustration of an apparatus for semiconductor device singulation. 
       FIG. 2  illustrates a singulation process. 
       FIG. 3  illustrates a burr caused by a singulation process. 
       FIG. 4  illustrates a smear caused by a singulation process. 
       FIG. 5  shows a solder melt caused by a singulation process. 
       FIG. 6  illustrates cooling a singulation blade with deionized water. 
       FIG. 7  illustrates a singulation blade generating a kerf in a molded strip in accordance with some embodiments of the invention. 
       FIG. 8  illustrates cooling and lubricating a singulation blade, and rinsing a kerf, with a synthetic lubricant according to some embodiments of the invention. 
       FIG. 9  compares the surface tension of deionized water with the surface tension of a synthetic lubricant. 
       FIG. 10  presents the results of a delamination test immediately after singulation. 
       FIG. 11  presents the results of a delamination test after a brief exposure to stress conditions at high heat. 
       FIG. 12  illustrates a high speed singulation process according to some embodiments of the invention. 
   

   DETAILED DESCRIPTION 
   In the following description, numerous details and alternatives are set forth for purpose of explanation. However, one of ordinary skill in the art will realize that the invention can be practiced without the use of these specific details. In other instances, well-known structures and devices are shown in block diagram form to not obscure the description of the invention with unnecessary detail. 
     FIG. 1  is an illustration of a system for semiconductor device singulation. As shown in this figure, the system  100  includes a singulation blade  105 , a molded strip  110 , a dicing tape  115 , and a kerf  120 . The molded strip  110  typically includes a number of semiconductor devices that are fabricated on sheets comprising various combinations of metal, semiconductor, and molding material. The sheets of different fabrication processes and with different die have various sizes and shapes before the sheets are diced by a singulation process to yield the individual semiconductor devices. The dicing tape  115  is typically an adhesive (dicing) tape that is used in the fabrication process. 
   During the singulation process, the blade  105  is applied to the molded strip  110 . When applied to the molded strip, the blade  105  typically cuts into or through the molded strip  110 , which generates the kerf  120 . The kerf  120  has substantially parallel walls cut into the molded strip, spaced apart from each other approximately the thickness of the blade. Preferably, the blade  105  rotates at a high rate of speed. In some embodiments, the spindle speed of the blade  105  is approximately 30,000 to 50,000 rotations per minute (RPM), while in some embodiments the table speed is approximately 4-10 inches per second (IPS). Without the invention, cutting the molded strip  110 , generation of the kerf  120  and the high speed rotation of the blade would cause a number of undesirable effects. For instance, high speed rotation of the blade  105  would cause the blade  105  to undesirably reach a higher temperature. An overheated blade  105  would cause (1) premature wear on the blade and (2) undesirable defects in the singulated product. 
   Moreover, generation of the kerf  120  produces a large amount of loose sawed particles, which, without the invention, would come to rest within the kerf  120 . The particles within the kerf  120  can increase the coefficient of friction of the blade  105  against the walls of the kerf  120 , and increase the power consumed to operate the blade  105 , while lowering the rate of cutting through the molded strip  110  and the dicing tape  115 . Also, particles can get caught and bind between the blade  105  and the walls of the kerf  120 . The increased friction on the blade  105  and the longer cutting time, further increase the temperature of the blade  105 , and thus exasperate the problems caused by an overheated blade: (1) premature blade wear and (2) defects in the singulated product. 
     FIG. 2  illustrates a closer view of the system  200  during a singulation process. As shown in  FIG. 2 , the blade  205  of some embodiments is comprised of several grits  206  secured by a resin  207 . The grits  206  are typically formed out of diamond or another suitable substance. As the grits  206  contact the molded strip  210 , a number of loose sawed particles  225  undesirably accumulate in the kerf  220 , which undesirably degrades the cutting efficiency of the blade  205 . As mentioned above, the application of the blade  205  in the kerf  220  typically generates an undesirable amount of heat that can cause several types of defects in the singulated product.  FIGS. 3 ,  4  and  5  illustrate examples of some of these defects. 
   For instance,  FIG. 3  illustrates a burr caused by a singulation process. As shown in this figure, a lead frame  300  has several leads  305 . The lead frame  300  has undergone a singulation process in which undesirable particles in the kerf and an overheated blade has caused the burrs  310  and  315  in the leads  305  on a side of the leadframe  300 . Also illustrated in this figure, the burrs are caused in one or more directions, for example, the X-direction  310  and/or the Y-direction  315 . A Z-direction burr  420 , is illustrated in  FIG. 4 .  FIG. 4  presents a side view of the leads  305  of the lead frame  300 .  FIG. 4  also illustrates a smear  425  between the leads  305  of the leadframe  300  caused by a singulation process. As shown in this figure, the smear  425  brings the leads  305  of the leadframe  300  undesirably near each other. 
     FIG. 5  shows a solder melt caused by a singulation process. As shown in this figure, the lead  505  of a leadframe has an undesirable solder melt  550  that has oozed beyond the boundary of the lead  505 . As mentioned above, the solder melt  550  is often caused by an overheated blade. 
   Also mentioned above, various attempts have been made to cool the blade.  FIG. 6  illustrates a system  600 , which attempts to cool a singulation blade  605  with deionized water  630 . However, as shown in this figure, deionized water does not operate adequately to (1) cool the blade  605 , particularly at higher spindle and/or table speeds, (2) lubricate the blade  605 , and (3) remove the buildup of particles  625  from the kerf  620 . 
   Accordingly,  FIG. 7  illustrates a system  700  for cooling and lubricating a singulation blade  705 , and rinsing a kerf  720 , with a temperature control device  730  and a synthetic lubricant according to some embodiments of the invention. As shown in  FIG. 7 , the temperature control device  730  is coupled to a chiller module  745 , which is coupled to a reservoir  740 . The reservoir  740  typically stores a fluid, such as, for example, the synthetic lubricant, distilled water, and/or a combination thereof. The chiller module  745  receives the synthetic lubricant or other fluid from the reservoir  740 , and chills or cools it. Some embodiments cool the synthetic lubricant to a temperature of approximately 20 degrees Celsius. However, other temperatures, including cooler temperatures, are achieved by the chiller module  745 . As the chiller module  745  cools the synthetic lubricant, the blade  705  typically generates a kerf  720  in a molded strip. While the kerf  720  is generated, the temperature control device  730  directs the cooled synthetic lubricant in particular ways. 
     FIG. 8  illustrates a top view of the operation of the temperature control device  730 , according to some embodiments. As shown in this figure, the temperature control device  730  of these embodiments applies a synthetic lubricant  735  towards several locations of the blade  705 , as well as directly at the cutting locus of the blade  705 . Further the temperature control device  730  injects the synthetic lubricant  735  directly into the kerf  720 . To accomplish the multi-point and/or multi-stage delivery of the synthetic lubricant  735 , the temperature control device  730 , of some embodiments, employs one or more nozzles for directing the synthetic lubricant  735 . The application method of these embodiments, achieves superior results over the art. 
   Moreover, the properties of the synthetic lubricant has superior properties over conventionally used deionized water for cooling and lubricating the blade, and for flushing the kerf. For example,  FIG. 9  compares the surface tension of deionized water with the surface tension of a synthetic lubricant. As shown in this figure, the deionized water tends to form a high tension bead  910  on a surface of the blade  705 . The high tension bead  910  forms a large bead angle (alpha), which prevents the deionized water from distributing over a greater surface of the blade  705 . Further, the high tension bead  910  has a high profile with respect to the surface of the blade  705  and, thus, does not penetrate between the blade  705  and the loose particles in the kerf. As further shown in this figure, the synthetic lubricant  915  has a lower surface tension than the deionized water and the synthetic lubricant  915  is distributed at a lower angle (beta) over a broader surface of the blade  705 . Thus, the synthetic lubricant covers a greater surface area and enters tighter regions formed between the blade and the loose particles within the kerf. 
   EXPERIMENTAL RESULTS 
   Several experiments were conducted to determine the efficacy of the method and system employing the synthetic lubricant of the embodiments described above.  FIG. 10  presents the results  1000  of a delamination test immediately after singulation. The results  1000  presented in this figure compare a high speed singulation process  1010  versus a conventional singulation process  1005 . As shown in this figure, the products of the high speed singulation process  1010  exhibit no incidences of singulation defects over the conventional lower speed process  1005 . However, the high speed singulation process  1010  is performed at a blade spindle rotation rate of approximately 30,000 to 50,000 RPM and/or a table speed of approximately 4 to 10 IPS. Moreover, the blade of the embodiments described above draws current of about 1.9 Amps. In contrast, the conventional singulation process draws about 3.5 Amps, while cutting laterally through the molded strip at only about 2.0 IPS, and at a spindle speed of only 20,000 RPM. 
     FIG. 11  presents the results  1100  of a delamination test after a brief exposure to high heat stress conditions. The heat stress conditions were applied after singulation by autoclaving at 260° C., 15 psi, 100% relative humidity, then infrared and/or conventional (wire) heating reflow, three times. These results  1100  compare a high speed singulation process  1110  versus a conventional singulation process  1105 . As presented in this figure, the high speed singulation process  1110  exhibited no incidences of singulation defects over the conventional singulation process  1105 , despite operating at a higher speed. 
     FIG. 12  summarizes the high speed singulation process  1200  of some embodiments of the invention. As shown in this figure, the process  1200  begins at the step  1205 , where the blade rotates at a high RPM. As mentioned above, the blade of some embodiments rotates at a spindle speed of approximately 30,000 to 50,000 RPM, and/or cuts at table speed of 4-10 IPS. However, one of ordinary skill will recognize that higher blade speeds are achieved by additional embodiments. Next, at the step  1210 , the blade is applied to a molded strip that has one or more semiconductor devices on the molded strip. Then, at the step  1215 , the synthetic lubricant is directed toward the blade. The synthetic lubricant will tend to cool the blade. At the step  1220 , the synthetic fluid is directed toward the cutting locus of the blade to lubricate the blade. The improved blade lubrication lowers the coefficient of friction between the blade and the cutting locus, which further lowers the temperature of the blade, and/or power consumption. In some embodiments, the overall power consumption is from 3.5 Amps to about 1.9 Amps. Next, at the step  1225 , some embodiments inject the synthetic lubricant directly into the kerf. This tends to loosen the sawed particles in the kerf. At the step  1230 , the synthetic lubricant further acts to rinse the kerf of the particles. Then, the process  1200  concludes. 
   ADVANTAGES 
   As described above, some embodiments of the invention provide a method and system for using a synthetic lubricant in a singulation process. The combination of an appropriate synthetic lubricant and an effective cooling device, together with a process for applying the device and lubricant, overcomes the drawbacks of high temperature and blade wear rate. For instance, the cooler running blade reduces metal fatigue and extends the effective cutting efficiency and useful life of the blade. Additionally, the cooler running blade typically operates at higher rotations per minute (RPM) and/or inches per second (IPS), in terms of spindle and/or table speeds, which results in faster and more efficient singulation for semiconductor fabrication. The result is a higher throughput than the conventional singulation process without a tradeoff in the quality of the singulated product. 
   While the invention has been described with reference to numerous specific details, one of ordinary skill in the art will recognize that the invention can be embodied in other specific forms without departing from the spirit of the invention. Thus, one of ordinary skill in the art will understand that the invention is not to be limited by the foregoing illustrative details, but rather is to be defined by the appended claims.