P/00/0 11 Regulation 3.2 AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT ORIGINAL TO BE COMPLETED BY APPLICANT Name of Applicant: Taiwan Shan Yin Int'l Co., Ltd. Actual Inventor(s): Taiwan Shan Yin Int'l Co., Ltd. Address for Service: A.P.T. Patent and Trade Mark Attorneys PO Box 222, Mitcham, SA 5062 Invention Title: A Roof Screw The following statement is a full description of this invention, including the best method of performing it known to me/us:- A ROOF SCREW BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw design, particularly to a roof screw. 5 2. Description of the Related Art Referring to Fig. 1, a conventional roof screw 1 comprises a head portion 1, a shank portion 12 outward extended from the head portion 11, and a drilling portion 13 disposed at a distal end of the shank portion 12. The shank portion 12 further includes a naked section 121 connected to the head portion 11, a threaded section 122 with 0 threaded units 123 disposed between the naked section 121 and the drilling portion 13, and a pair of symmetrical wings 124 protrudently formed between the naked section 121 and the threaded section 122. A sided flange of each wing 124 is restrained outwardly and downwardly from the shank portion 12 so as to form a cutting surface 125, thereby contributing to a cutting knife 126 protruded at a tip of the cutting surface 5 125. In operation, the roof screw 1 is to be fastened to a corrugated board 2. Herein, the drilling portion 13 firstly penetrates the corrugated board 2, and then the cooperation of the cutting surface 125 and the cutting knife 126 allows a through hole 21 to be cut out on the corrugated board 2. Accordingly, the shank 12 is able to go 0 through the through hole 21. Continuingly, the roof screw 1 does not stop entering a frame 3 until the wings 124 prop against the frame 3. As a result, a firm engagement is achieved, and the roof screw 1 does not improperly damage the corrugated board 2 in view of an over-deep drilling. 2 However, shortcomings exist in the conventional roof screw 1 as follows: 1. The symmetrical wings 124 are formed by compression, which adversely causes the unsatisfactory cutting strength thereof since the compressed wings 124 are actually formed into thin flakes. As a result, when the cutting stress falls on the cutting 5 edges 126, the thin wings 124 might be broken. Therefore, the wings 124 are unable to efficiently cut out a smooth through hole 21 on the corrugated board 2. Unbeneficially, an interstice is generated between the fastened roof screw 1 and the corrugated board 2, and the rain might permeate into the interstice and erode the roof screw 1. 2. Further, the wings 124 are outwardly and downwardly formed from the 0 shank portion 12, so the cutting surfaces 125 are able to take shape of a restrained arrangement. Herein, disposed at tips of the restrained cutting surfaces 125, the cutting edges 126 unavoidably bear a large contact stress during the drilling. Thereby, the cutting edges 126 might become blunt or ruptured in view of the large contact stress. Accordingly, the cutting edges 126 and the cutting surfaces 125 can not smoothly 5 incise the corrugated board 2, which influences the screwing speed as well as incurs an unstable fastening effect. 3. Afore wings 124 of the think flake formation are readily broken or damaged in view of the poor bearing strength; the broken wings 124 might result in the inconsistent sizes. As a result, the roof screw 1 (as shown in Fig. 2) is subject to slant 0 since the wings 124 can not prop against the frame 3 with a consistent propping manner. Thereby, the head portion 11 is incapable of firmly staying close to the corrugated board 2, which influences the fixing effect of the roof screw 1. Disadvantages as depicted above should be amended. 3 SUMMARY OF THE INVENTION It is therefore the purpose of this invention to provide a roof screw that is able to precisely and speedily incise a corrugated board as well as prevents from breakage so as to achieve a preferred fastening effect. 5 The roof screw in accordance with the present invention comprises a head portion, a shank portion outward extended from the head, and a drilling portion disposed at a distal end of the shank portion. Wherein, the shank portion includes a naked section, a threaded section, and correspondent wings protruded between the naked section and the threaded section. A cutting surface on the wing is inclined with 0 respect to a central line of the shank portion for radiating therefrom. An auxiliary wing is extended from a top end of the wing toward the head portion. One auxiliary wing that is disposed with a frontward tilt is extended away from the wing that is disposed rearward, and the other auxiliary wing that is disposed with a rearward tilt is extended away from the wing that is arranged frontward. An included angle is accordingly formed by the 5 wing and the auxiliary wing. The cooperation of the wing and the auxiliary wing contributes to an increased strength for the wing structure. Further, the respective inclinations brought about by the wings and the auxiliary wings preferably allow cutting edges of the wings to render a gradual cutting effect. As a result, the cutting edges are able to sharply carve the corrugated board, and the wings are capable of speedily 0 incising the same so as to obtain a firm fastening effect. Preferably, a junction of the top end of the wing and the auxiliary wing is designed by an arc. 4 Preferably, a first diameter of the naked section is larger than a second diameter of the threaded section. Preferably, the cutting edges of the wings are respectively disposed along a frontward inclination and a rearward inclination, thereby resulting in a frontward wing 5 and a rearward wing contrary to said frontward wing, respectively. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing a conventional screw in screwing; Fig. 2 is a schematic view showing the conventional screw in screwing; Fig. 3 is a perspective view showing a first preferred embodiment of the present 0 invention; Fig. 4 is a side view of Fig. 3; Fig. 5 is a schematic view showing the first preferred embodiment of the present invention in screwing; Fig. 6 is a schematic view showing the first preferred embodiment of the present 5 invention in screwing; Fig. 7 is a perspective view showing a second preferred embodiment of the present invention; and Fig. 8 is a side view of Fig. 7. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 0 Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. Referring to Figs. 3 and 4, a first preferred embodiment of the present invention is shown. A roof screw 4 comprises a head portion 41, a shank portion 42 5 outward extended from the head portion 41, and a drilling portion 43 disposed at a distal end of the shank portion 42. In the embodiment, the drilling portion 43 may adopt either a drilling end or a tapered end according to the practical operation or the applied material. Herein, the drilling portion 43 adopts the drilling end. 5 Continuingly, the shank portion 42 includes a naked section 421 connected to the head portion 41, a threaded section 422 with threaded units 423 disposed between the naked section 421 and the drilling portion 32, and correspondent wings 424 protrudently disposed between the naked section 421 and the threaded section 422. Preferably, a first diameter D of the naked section 421 is larger than a second 0 diameter d of the threaded section 422. Additionally, the wing 424 includes a cutting surface 4241 formed on the shank portion 42 and extended relatively to a direction from the head portion 41 toward the drilling portion 43, a valley 4242 disposed between the cutting surface 4241 and the shank portion 42, and a cutting edge 4243 formed at a convergence of the valley 4242 and the cutting surface 4241. The cutting 5 surface 4241 of the wing 424 is inclined with respect to a central line of the shank portion 42 for radiating therefrom. This embodiment adopts two wings 424 disposed relatively. The cutting edges 4243 of the wings 424 are respectively disposed along a frontward inclination and a rearward inclination, thereby resulting in a frontward wing and a rearward wing contrary to the frontward wing, respectively. 0 Favorably, an auxiliary wing 425 is further extended from a top end of the wing 424 toward the head portion 41. One auxiliary wing 425 that is disposed with a frontward tilt is extended away from the rearward wing, and the other auxiliary wing 425 that is disposed with a rearward tilt is extended away from the frontward wing. 6 Accordingly, an included angle a is formed by the wing 424 and the auxiliary wing 425. Referring to Figs. 4 to 6, in operation, the drilling portion 43 of the roof screw 4 enters a corrugated board 5. Rotated along with the threaded units 423, the shank 5 portion 42 is subsequently inserted into a frame 6. Herein, when the wings 424 contacts the corrugated board 5, the cutting edges 4243 of the wings 424 thence incise the corrugated board 5 with a through hole 51. Advantageously, the wing formed with the frontward inclination and the wing formed with the rearward inclination as well as the radially extended cutting surfaces 4241 are able to 0 progressively cut through the corrugated board 5, which evenly distributes the contact stress over the entire wings 424. Thus, the wings 424 do not bear a large contact stress anymore, and the broken wings could be avoided. The structure of the wing 424 and the auxiliary wing 425 including the included angle a allows the preferable strength to be contained therein. The strength is even 5 stronger than that of the conventional flake-like wings. Moreover, the cutting stress while incising the corrugated board 5 is able to be evenly distributed over the entire wings 424 and the auxiliary wings 425. Thus, the wings 424 do not break easily since the auxiliary wings 425 provide an additional supporting force for the wings 424. Finally, while arranging the valley 4242 on each wing 424, the cutting edge 4243 is 0 accordingly shaped into a razor-sharp formation to enhance the cutting efficiency. Thereby, the through hole 51 could be more preferably and rapidly carved and reamed. Advantageously, the debris generated during cutting could be timely expelled via the valley 4242 so as to allow the roof screw 4 to fasten the corrugated 7 board 5 tightly. Whereby, thanks to the wings 424 and the auxiliary wings 425, a preferable and firm fastening effect is achieved, and an effort-saving as well as a speedy cutting performance is obtained. Referring to Figs. 7 and 8, a second preferred embodiment is shown. The roof 5 screw 4 similarly comprises the like elements such as the head portion 41, the shank portion 42, and the drilling portion 43. The correspondent functions and the accordant correlations same to those of the first preferred embodiment are herein omitted. In this embodiment, a junction of the top end of the wing 424 and the auxiliary wing 425 is designed by an arc. Accordingly, the combination of the wings 424 and the auxiliary 0 wings 425 is able to offer a stronger incising force. Moreover, the progressive cutting manner preferably decreases the cutting stress. Thus, a speedy carving and a favorable fastening effect are both obtained. To sum up, the present invention in particularly utilizes the wings that are not only disposed inclined with respect to the central line of the shank portion for radiating 5 therefrom but also arranged crosswise with each other to cooperate with the auxiliary wings extended from the top ends thereof. By means of the opposite disposing manners, the wing and the auxiliary wing further form an included angle therebetween for increasing supporting force to the wings. Thus, the cutting edge on the wing and the included angle allow the roof screw to enter the corrugated board with a sharp, 0 speedy, and progressive way. Preferably, disadvantages like the broken wings or the weak bearing force are avoided, which ensures the firm fastening effect of the present invention. 8 While we have shown and described the embodiment in accordance with the present invention, it should be clear to those skilled in the art that further embodiments may be made without departing from the scope of the present invention. 5 9