FONG, K.K. (AEM Singapore Pte Ltd, 52 Serangoon North Avenue 4, Singapore 3, 55585, SG)
PALANI, Arun (AEM Singapore Pte Ltd, 52 Serangoon North Avenue 4, Singapore 3, 55585, SG)
FANG, C.P. (AEM Singapore Pte Ltd, 52 Serangoon North Avenue 4, Singapore 3, 55585, SG)
TAN, Wee Soon (AEM Singapore Pte Ltd, 52 Serangoon North Avenue 4, Singapore 3, 55585, SG)
FONG, K.K. (AEM Singapore Pte Ltd, 52 Serangoon North Avenue 4, Singapore 3, 55585, SG)
PALANI, Arun (AEM Singapore Pte Ltd, 52 Serangoon North Avenue 4, Singapore 3, 55585, SG)
FANG, C.P. (AEM Singapore Pte Ltd, 52 Serangoon North Avenue 4, Singapore 3, 55585, SG)
CLAIMS
1. A water jet nozzle comprising: a main body formed from a first material; a downstream surface comprising an orifice; and an upstream surface comprising a chamber extending towards the orifice; wherein at least a circumferential wall defining the orifice is coated with a second material, the second material having a greater hardness compared to the first material.
2. The water jet nozzle as claimed in claim 1 , wherein the coating extends over at least a portion of a wall defining the chamber.
3. The water jet nozzle as claimed in claims 1 or 2, wherein the downstream surface further comprises a V groove and the orifice is formed at a bottom portion of the V groove.
4. The water jet nozzle as claimed in claim 3, wherein the coating extends over at least a portion of the bottom portion of the V groove adjacent the orifice.
5. The water jet nozzle as claimed in claims 3 or 4, wherein the V groove is formed in a recess formed in the downstream surface.
6. The water jet nozzle as claimed in claim 5, wherein the recess comprises substantially perpendicular side wall with respect to the downstream surface.
7. The water jet nozzle as claimed in any one of the preceding claims, wherein the chamber comprises, in a downstream order, a frusto-conical portion, a cylindrical portion, and a conical portion extending towards the orifice.
8. The water jet nozzle as claimed in any one of the preceding claims, wherein the orifice is elliptical.
8. The water jet nozzle as claimed in any one of the preceding claims, wherein the coating comprises a diamond coating.
9. The water jet nozzle as claimed in claim 7, wherein the diamond coating is formed using ionization.
10. A method of fabricating a water jet nozzle, the method comprising: providing a main body formed from a first material; forming a downstream surface comprising an orifice; and forming an upstream surface comprising a chamber extending towards the orifice; and coating at least a circumferential wall defining the orifice with a second material, the second material having a greater hardness compared to the first material.
11. The method as claimed in claim 10, further comprising forming the orifice as a substantially horizontally bent ellipse.
12. The method as claimed in claim 11 ; wherein parameters of the substantially horizontally bent ellipse are chosen such that the nozzle exhibits a desired spray angle.
13. The method as claimed in claims 11 or 12, wherein parameters of the substantially horizontally bent ellipse are chosen such that the nozzle exhibits a desired flow rate at a given water pressure.
11. A method of de-flashing packaged semiconductor devices, the method comprising directing a water jet towards the packaged semiconductor device using a water jet nozzle comprising: a main body formed from a first material; a downstream surface comprising an orifice; and an upstream surface comprising a chamber extending towards the orifice; wherein at least a circumferential wall defining the orifice is coated with a second material, the second material having a greater hardness compared to the first material. |
A Wear-Resistant High-Pressure Water Jet Nozzle
FIELD OF INVENTION
The present invention relates broadly to a water jet nozzle, to a method for fabricating a water jet nozzle, and to a method of de-flashing.
BACKGROUND
De-flashing processes are widely used in the semiconductor industry to remove unwanted flashes, which comprise of excess encapsulation material found around a semiconductor package. Generally, a semiconductor package comprises an encapsulated portion 130 with leads 120 and a heat sink 140 disposed at each end of the encapsulated portion 130. During the moulding process, unwanted flashes 110 may be present around the encapsulated portion 130 and over the leads 120 of a semiconductor package 100 as seen in Figure 1A.
After the moulding process, the lead portion 120 of the semiconductor package 100 is plated. However, due to the presence of the unwanted flashes 1 10, the lead portion 120 under these unwanted flashes 110 will not be plated. During the operation, the unwanted flashes 110 may break down and expose the un-plated lead portion 120 to the atmospheric air. This will result in the lead portion 120 to be oxidized by the atmospheric air and become weakened. The weakened lead portion 120 can ultimately lead to product failure.
There are currently a number of high-pressure water jet nozzles designs in the market. An example is a nozzle which has an insert incorporated therein which defines an orifice. Typically, such nozzles create diverting spray from the orifice. This insert is made of hard materials such as whole diamond, sapphire or ruby. This insert is fixed into the nozzle by means such as glue or sinter. As this insert is constantly subject to the pressure resulting from the thrust of the water flow, therefore most of the pressure is concentrated at the recess. This results in the weakening of the bond between the insert
and the nozzle. As this weakening continues, the insert made of whole diamond, sapphire or ruby can be dislodged from the nozzle. Furthermore, high-pressure water jet nozzles using inserts made of whole diamond, sapphire or ruby are expensive.
Further, one of the processes to remove the unwanted flashes, i.e. de-flashing, comprises two steps: electro chemical immersion/chemical immersion followed by high- pressure water jet de-flashing. In electro chemical immersion/chemical immersion, the semiconductor packages are immersed in a chemical which is carried by a belt apparatus at an appropriate speed to satisfy the 'chemical immersion timing'. Typically, this normal timing varies between 60-90 seconds. After the chemical immersion, the unwanted flashes are softened and are removed by a high-pressure water jet de-flashing by the thrust force of the water jet produced by a high-pressure water jet nozzle. A semiconductor package with the unwanted flashes 110 removed is as illustrated in Figure 1B. In electro chemical immersion, there is an additional step of supplying an electric current to the semiconductor packages by a rectifier to enhance the softening process.
The high-pressure water jet nozzle used to remove the unwanted flashes from semiconductor packages should efficiently convert the pressure energy into kinetic energy i.e. thrust force, and the nozzle should be wear-resistant. A wom-off nozzle can diminish the nozzle performance, thus directly affecting the quality of de-flashing.
Presently in the semiconductor industry, straight water jet nozzles are also used to remove unwanted flashes. A disadvantage in using straight water jet nozzles is that the length of the water spray and the target area cannot vary. Furthermore, water sprayed by straight water jet nozzles may affect other parts of the semiconductor packages, thus causing unnecessary damage to the product.
Hence, there is a need to provide a high-pressure water jet nozzle, which seeks to address one or more of the above-mentioned problems.
SUMMARY
In accordance with a first aspect of the present invention there is provided a water jet nozzle comprising a main body formed from a first material; a downstream surface comprising an orifice; and an upstream surface comprising a chamber extending towards the orifice; wherein at least a circumferential wall defining the orifice is coated with a second material, the second material having a greater hardness compared to the first material.
The coating may extend over at least a portion of a wall defining the chamber.
The downstream surface may further comprise a V groove and the orifice is formed at a bottom portion of the V groove.
The coating may extend over at least a portion of the bottom portion of the V groove adjacent the orifice.
The V groove may be formed in a recess formed in the downstream surface.
The recess may comprise substantially perpendicular side walls with respect to the downstream surface.
The chamber may comprise, in a downstream order, a frusto-conical portion, a cylindrical portion, and a conical portion extending towards the orifice.
The orifice may be elliptical.
The coating may comprise a diamond coating.
The diamond coating may be formed using ionization.
In accordance with a second aspect of the present invention there is provided a method of fabricating a water jet nozzle, the method comprising providing a main body formed from a first material; forming a downstream surface comprising an orifice; and forming an upstream surface comprising a chamber extending towards
the orifice; and coating at least a circumferential wall defining the orifice with a second material, the second material having a greater hardness compared to the first material.
The method may further comprise forming the orifice as a substantially horizontally bent ellipse.
Parameters of the substantially horizontally bent ellipse may be chosen such that the nozzle exhibits a desired spray angle.
Parameters of the substantially horizontally bent ellipse may be chosen such that the nozzle exhibits a desired flow rate at a given water pressure.
In accordance with a third aspect of the present invention there is provided a method of de-flashing packaged semiconductor devices, the method comprising directing a water jet towards the packaged semiconductor device using a water jet nozzle comprising a main body formed from a first material; a downstream surface comprising an orifice; and an upstream surface comprising a chamber extending towards the orifice; wherein at least a circumferential wall defining the orifice is coated with a second material, the second material having a greater hardness compared to the first material.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will be better understood and readily apparent to one of ordinary skill in the art from the following written description, by way of example only, and in conjunction with the drawings, in which:
Figure 1A shows unwanted flashes present around the encapsulated portion and over the leads of a conventional semiconductor package;
Figure 1 B shows unwanted flashes removed from the encapsulated portion and over the leads of the conventional semiconductor package;
Figures 2A and 2B are perspective views of a high-pressure nozzle assembly in accordance with an embodiment of the present invention;
Figures 3A and 3B are perspective views of a nozzle in accordance with an embodiment of the present invention;
Figure 4 is another perspective view of the nozzle in accordance with an embodiment of the present invention;
Figure 5A and 5B are cross-sectional views of the nozzle in accordance with an embodiment of the present invention;
Figure 6A shows an exemplary view of a high-pressure water jet spray in accordance with an embodiment of the present invention;
Figure 6B illustrates the principle of a water jet spray to achieve water jet spray in accordance with an embodiment of the present invention;
Figure 7 shows a graph illustrating pressure against flow rate in accordance with an embodiment of the present invention.
Figure 8 shows a flow chart illustrating a method of fabricating a water jet nozzle according to an example embodiment.
DETAILED DESCRIPTION
Figure 2A shows a perspective front view of a high-pressure nozzle assembly 200 in an example embodiment. Figure 2B shows a perspective rear view of the high- pressure nozzle assembly 200 in an example embodiment. The high-pressure nozzle assembly comprises of a mounting cap 210, a nozzle 220 and a base member 230.
The mounting cap 210 comprises of a downstream surface 290, a chamfer 240 near a hole 250 along the axis of the mounting cap 210. The mounting cap 210 further comprises a cylindrical surface 280, an internal chamfer 260, a side chamfer 270 and four flat surfaces 255. The internal chamfer 260 is disposed near the edge of the chamfer 240, while the side chamfer 270 is disposed near the edge of the downstream surface 290. The four surfaces 255 are disposed substantially perpendicularly to each other, around the mounting cap 210.
The base member 230 comprises of a side chamfer 205 that is disposed near a flat surface 215. A thread 245 is disposed near a cylindrical surface 225, which is situated towards the edge of a flat surface 235. The thread 245 comprises of a plurality of grooves to facilitate connection to a water source. A thread 275 is situated at the opposing end of thread 245 to facilitate connection to the mounting cap 210. A cylindrical surface 225 is disposed near the flat surface 235, a side chamfer 265 and another cylindrical surface 255.
Figure 3A shows a perspective front view of the nozzle 220 in an example embodiment. Figure 3B shows a perspective rear view of the nozzle 220 in an example embodiment.
The nozzle 220 is cylindrical in shape. The nozzle 220 comprises of an downstream surface 415, a upstream surface 425 and a peripheral surface 420. The downstream surface 415 is parallel to the upupstream surface 425. The downstream surface 415 comprises of an recess 450a that is indented across the downstream surface 415 from one end to the other end. The recess 450a in this example embodiment has substantially perpendicular side walls with respect to the downstream surface 415. A chamber 450 is formed in the recess 450a. In this example embodiment, the chamber 450 is a substantially V groove. A chamfer 430 is disposed near the edge of the downstream surface 415 and along the edges of the recess 450a.
A chamfer 430a is disposed near the edge of the upstream surface 425. A chamber 475 is disposed centrally in the upstream surface 425. In this example
embodiment, the first chamber 475 comprises of a frusto-conical portion 440, a cylindrical recess portion 480 and a substantially conical portion 490.
An elliptical orifice 470 is located in the nozzle 220. The elliptical orifice 470 is disposed in the substantially V groove 450, which is formed in the recess 450a. The rear view of the elliptical orifice 470 can be seen in Figure 3B. The elliptical orifice 470 is the meeting point whereby the substantially V groove 450 converges with the substantially conical portion 490. As a result, the elliptical orifice 470 is shaped like a 'horizontally bent ellipse' in the example embodiment, instead of a "flat" round shape if the substantially conical portion would converge with a horizontal surface. The intersection of the substantially V groove 450 and the substantially conical portion 490, in defining the elliptical orifice 470 also determines the spray angle from the nozzle 220. Depending on the exact shape of configuration of the substantially V groove 450 and the substantially conical portion 490 in different example embodiments, different spray angles can thus be achieved. Instead, a round orifice would create a round water jet stream with substantially zero spray angle (straight water jet).
The calculations of the elliptical orifice 470 of one example embodiment of the present invention are as shown below, whereby P is the pressure of the water and Q is the rate at which the water flows:
Diameter of the elliptical orifice d mm = ( (2.77 x Q 2 ) í P )° 25
A mm 2 = 3.14x(</ 2 ) í4
The values of P and Q are typically determined by the quality requirements of de- flashing of the semiconductor packages. For example, since semiconductor packages come in different sizes, nozzles with different specifications can be provided depending on different applications. Generally, there is a balance with high pressure resulting in the lead portion of a semiconductor package to bend, and lower pressure resulting in poor quality of the de-flashing. Cross-sectional area of elliptical orifice 3.14 x rl x ri
Impact force 0.024 χ β χ P 05
Upon determining the equivalent diameter of the elliptical orifice 470 to produce a desired flow rate of the water, it is then possible to determine the equivalent surface area of the elliptical orifice 470. Thereafter, the major and the minor radii can be obtained by selecting a value for either one of the radii and calculate the other.
Figure 4 shows a top view of the nozzle tip 220. The major axis of the elliptical orifice 470 is substantially parallel to the recess 450a.
Figure 5A shows a side cross-sectional view of the nozzle 220. The substantially V groove 450 is disposed near the downstream surface 415 while the substantially conical portion 490, the cylindrical recess 480 and the frusto-conical portion 440 are disposed near the upstream surface 425 of the nozzle 220. The proportion of the substantially V groove 450 and the proportion of the frusto-conical portion 440, the cylindrical recess 480 and the substantially conical portion 490 can be seen in Figure 5A, marked A and B respectively. The depth of the substantially V groove 450 is smaller than the depths of the substantially conical portion 490, the cylindrical recess 480 and the frusto-conical portion 440 combined. The water source enters the nozzle assembly 200 from the base member 230, flows through the nozzle 220 and exits the nozzle assembly 200 from the mounting cap 210.
Figure 5B shows another side cross-sectional view of the nozzle 220. As governed by the Bernoulli effect, the pressure of the water decreases as its velocity increases and vice versa. Thus, the pressure and velocity are inversely proportional to one another.
The Bernoulli effect can be considered to be a statement of the conservation of energy principle as applied to flowing fluids. The qualitative behaviour that is usually labelled with the term "Bernoulli effect" is the lowering of fluid pressure in regions where flow velocity is increased. For the nozzle 220 shown in Figure 5B, the following Bernoulli equation may be derived.
Pressure energy + Kinetic Pressure energy + Kinetic energy/unit volume + Potential energy/unit volume + Potential energy/unit volume at section A energy/unit volume at section B
As can be seen from the above Bernoulli equation, the fluid pressure in Section B of Figure 5B where the flow velocity increases, is therefore lower than in Section A of Figure 5B, which exhibits higher pressure and lesser kinetic energy. Therefore, the nozzle 220 in this example embodiment can advantageously reduce the fluid pressure at and around the elliptical orifice 470, thereby reducing wearing of the diamond coating 460, 460a in that area. Hence advantageously, the lifespan of the nozzle 220 can be prolonged.
This unique design and proportion of the substantially V groove 450, the frusto- conical portion 440, the cylindrical recess 480 and the substantially conical portion 490 facilitate smooth flow of the water out of the nozzle assembly 200, thus reducing the impact of the thrust of the water flow on the nozzle 220. Hence, this advantageously further assists in prolonging the lifespan of the nozzle 220.
The surfaces of the recess 450a, the substantially V groove 450, the frusto-conical portion 440, the cylindrical recess 480 and the substantially conical portion 490 are coated with a layer of a hard material such as, but not limited to, diamond particles. In this example embodiment, a layer of fine diamond particles is coated onto the recess 450a, the substantially V groove 450, the frusto-conical portion 440, the cylindrical recess 480 and the substantially conical portion 490 by using known methods, including but not limited to e.g. ionization, to form a diamond coating 460, 460a, as shown in Figure 5A.
More particular, the nozzle 220 is first charged and diamond particles are ionized to facilitate the bonding of the diamond particles to surfaces of the recess 450a, the substantially V groove 450, the frusto-conical portion 440, the cylindrical recess 480 and the substantially conical portion 490, to form a layer of diamond coating 460, 460a. This layer of diamond coating 460, 460a is approximately 3 microns thick in this example embodiment. The entire coating process is controlled by the density of the carbon molecules in the diamond particles. The hard material such as diamond, in this example embodiment, used to coat the surfaces of the recess 450a, the substantially V groove 450, the frusto-conical portion 440, the cylindrical recess 480
and the substantially conical portion 490 can advantageously prolong the lifespan of the nozzle 220 substantially.
The coating 460, 460a serves as a protective layer on the recess 450a, the substantially V groove 450, the frusto-conical portion 440, the cylindrical recess 480 and the substantially conical portion 490, against the strong thrust of the water spray. As the layer of diamond coating 460, 460a is bonded onto the recess 450a, the substantially V groove 450, the frusto-conical portion 440, the cylindrical recess
480 and the substantially conical portion 490 by means of charging and ionization in this example embodiment, the diamond particles are not easily dislodged. In addition, as fine diamond particles rather than whole diamonds are used, this substantially reduces the manufacturing costs of the nozzle 220.
Figure 6A shows the high-pressure water jet nozzle assembly 200, spraying water 720 at a high-pressure, against unwanted flashes 710 to remove them. The water 720 is being forced out of the nozzle assembly 200 at an angle to target at the key area, i.e. the unwanted flashes 710.
Figure 6B shows the relationship between the water 720 sprayed at an angle 730, a distance 740 of the water spray and a target area 750. In one embodiment of the present invention, when the angle 730 is 30° the length of the water spray distance 740 is approximately 15mm, while the target area of the water spray is approximately 7.5mm. This means that the water spray can be targeting unwanted flashes 710 with a surface length 750 of about 7.5mm.
Figure 7 shows a graph illustrating pressure against flow rate for one example nozzle design. It will be appreciated similar charts can be created for different nozzle designs. Since different products typically need different pressure ranges for effective deflashing, such data presentation charts can provide a a convenenient reference for determining/choosing a suitable a design for a particular product, and for facilitating determination of the supply size based on number of nozzle, type of nozzle and working pressure.
Figure 8 shows a flow chart 800 illustrating a method of fabricating a water jet nozzle according to an example embodiment. At step 802, a main body formed from a first material is provided. At step 804; a downstream surface comprising an orifice is formed; and at step 806 an upstream surface comprising a chamber extending towards the orifice is formed. At step 808, at least a circumferential wall defining the orifice is coated with a second material, the second material having a greater hardness compared to the first material.
The described embodiment can provide a water jet nozzle that has a number of advantages over existing designs, including
- the use of a hard material coating instead of a bulk hard material, such as diamond, can significantly reduce the cost of manufacture
- the chamber design in the upstream surface leading to the orifice can assist in reducing the impact force on the hard material coating, thus further increase life time of the nozzle
- the orifice design can result in a diverting spray for selecting different design options for a working distance and area of de-flashing.
It will be appreciated by a person skilled in the relevant art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are therefore, to be considered in all respects to be illustrative and not restrictive.
Next Patent: WO/2009/154570