The dimension accuracy analysis of a micro-punching mold for IC packing bag

Transcription

1 The dimension accuracy analysis of a micro-punching mold for IC packing bag Wei-Shin Lin and Jui-Chang Lin * Associate professor, Department of Mechanical and Computer - Aided Engineering, National Formosa University, uwei, Yunlin, Taiwan. linwhs@nfu.edu.tw Professor, Department of Mechanical Design Engineering, National Formosa University, uwei, Yunlin, Taiwan. linrc@nfu.edu.tw, * Corresponding author Abstract This article is pointed to the dimension accuracy analysis of the micro-punching mold for plastic carrier tape. The parts dimensions of the punch were first determined by the specification of the plastic carrier tape. The parts would be manufactured and assembled, and the performance of the punch was tested subsequently. Variation of dimensional accuracy of the plastic carrier tape was inspected to evaluate the performance of the punch. Mean and variance test was conducted under the significance level of α =.5. Through these inspections, all the plastic carrier tape met the specifications of dimensional accuracy, which indicated that the precision and performance of the developed micro-punching mold also met the requirement. Keywords: Dimension accuracy, micro-punching mold, IC packing bag, plastic carrier tape, hypothesis testing. Introduction IC chips scrap each other during transportation. Also, the chips oxidization, when coming into water and air, results in poor quality products. The chips need to be well packed and to be protected from the environment. The method of Surface Mount Component (SMC) packing using plastic carrier tape is a solution that can reduce chip damage []. Plastic carrier tape is produced through the processes of extruding, vacuum forming, micro-punching and splitting. At the micro-punching process, the semi-product of plastic carrier tape is flowed through the micro-punching mold to punch the mold. The quality of the plastic carrier tape is almost decided by the performance of the micro-punching mold. Therefore, the dimension accuracy of the micro-punching mold is very important.. Statistical hypothesis testing theorem [, 3, 4] Usually, the allowance deviation of mechanical part is called tolerance in the machining process. If the nominal dimension of the part is x and the deviation is dimension could be marked as x, then it s x x. For example, when the dimension specification of a mechanical part is 5. mm, the machining dimension between 4.9 and 5. mm is 4-7

2 allowed. When execute quality control, the upper and lower allowance deviation of the part was usually taken as the upper and lower control limit [5]. If the dimension distribution of the part followed the normal distribution, the mean value would be the nominal dimension and the standard deviation would be closed to x x x x x () 6 3 As the 3σ rule of normal distribution, the dimension of the part fall in the range of x x would be %. When the production development is proceeding, dimension testing is required for insuring the specification of the part. The pre-product is tested and measured, the sample mean and standard deviation was calculated, and then the hypothesis testing of the mean and the hypothesis testing of the variance was then proceeded. According to the statistical hypothesis testing theorem, the testing is like the following listed. () The hypothesis testing of the mean In order to ensure the dimension confirms with the specification of the product, two-tail testing is usually used in hypothesis testing. The statement of the null hypothesis and alternative hypothesis will be : and :, where, is the nominal dimension of the parts. In this study, a random sample of size n is used, the sampling distribution of the sample mean x will be approximate normal distribution with mean and standard deviation / n, if the null hypothesis is true. It is usually convenient to standardize the sample mean and use a test statistic based on the standard normal distribution. That is, the test procedure for : use the test statistic x z () / n If the null hypothesis : is true, E ( x), and the distribution of the test statistic z is the standard normal distribution [denote N(,)]. In this study, a fixed significance level testing is used. If : is true, the probability is that the test static z falls between z and - z, where z is the / percentage points of the standard normal distribution. When n = 3, and. 5, z z.96 and z z z. 96 /.5 /.975. So that, when.96 z. 96, the null hypothesis : is true. It is means that the nominal dimension of the parts fit the design specification. The distribution of z is as shown in Fig.. 4-8

3 Fig.. The distribution of z. Fig.. The distribution of the test statistic. () The hypothesis testing of the variance To further check if the dimension deviation confirmed with the specification, hypothesis testing of the variance is proceeded. Because the smaller the dimension variation, the better the dimension accuracy, the right tail testing is used. The null hypothesis and alternative hypothesis will be : and :. The test statistic will be ( n ) s (3) Where, is the variance of the design specification of the parts, s is the sample variance. If the null hypothesis is true, the test statistic follows the chi-square : distribution with n degree of freedom. With n = 3,. 5,the critical region n (, ) (.95,9) When 4. 56, the null hypothesis is true. It means the variance of : the dimension fit the design specification. The distribution of the test statistic is as shown in Fig.. 3. The design of the micro-punch mold After extruding and vacuum forming process, the hole punching process was implemented by micro-punching mold. The parts dimensions of the punching mold were decided by the dimension accuracy of the plastic carrier tape, the punching speed of the punch and the reliability requirement of the punching system. After manufactured and assembled, the performance of the punch must be tested. The assembled punch die was shown in Fig. 3 and the punched plastic carrier tape was shown in Fig

4 . Fig. 3. The assembled punch die. Fig. 4. The punched plastic carrier tape. 4. The test of the dimension accuracy In order to ensure the punch quality, the dimension about the punching process must be tested. When punching process was proceeded, the dimension A to E had to be controlled as shown in Fig. 5. As Fig. 5, dimension A was the distance between two pockets, dimension B was the diameter of the transmission hole, dimension C was the distance between the transmission hole, dimension D was the horizontal distance between the center of transmission hole and the center of pocket, and dimension E was the vertical distance between the center of transmission hole and the center of pocket. Fig. 5. The punch dimension of plastic carrier tape. Take a random sample size of n = 3 for the punched plastic carrier tape, measured the dimension A to E for each sample. Calculated the sample mean x and standard deviations, and then executed the testing with. 5. The test result was shown in Table. From Table, it can be found that the z value was fall in the accepted region, the null hypothesis : is true, it is means the nominal dimension confirms to the requirement. The all values were fall in the accepted region, the null hypothesis : is true, it is means the dimension deviation confirms to the requirement. Table.. The dimension accuracy test result. 4-

5 Dimension Specification x s z A B C D E Conclusion According to the statistical hypothesis testing theorem, focus on the punched plastic carrier tape, take a random sample size of n = 3, with significance level of. 5 to proceed hypothesis testing of mean and variance. From the testing results, it can be found () The sample mean of dimension A to E conformed to the design specification. () The sample variance of dimension A to E conformed to the design specification. (3) The function of the micro-punch mold fit in with the requirement based on the testing results. The dimension accuracy of the punched plastic carrier tape for IC packing bag conformed to the specification requirement. References. S.C. uang. Image detecting of paper carrier tape for chip packing in stamping process. Master thesis, Department of Dynamic Mechanical, National Formosa University, Taiwan. 3.. C.C. Chiang. Introduction to probability and statistics. Prentice all Press, Taiwan D.C. Montgomery, G.C. Runger and N.F. ubele. Engineering Statistics. 4 th ed., John Wiley& Sons, Inc W. Mendenhall, T. Sincich. Statistics for Engineering and the Sciences. 8 th ed., Pearson Prentice all, Inc., New Jersey T.. Chien and Y.. Li. Total Quality Management and Six Sigma. Gau Lih Book Co., Ltd., Taiwan