Effective Evaluation Method A new delamination test method for MUF (molded underfill) package

Transcription

1 2017 IEEE 67th Electronic Components and Technology Conference Effective Evaluation Method A new delamination test method for MUF (molded underfill) package Junghwa Kim 1, Seung Han 1, Woochul Na 1, SoYoon Kim 1, Ki Hyeok Kwon 1, Deokhoon Park 2, Donghwan Lee 1, Sang Kyun Kim 1 1 Development Group, Semiconductor Material Business Team, Samsung SDI Co., Ltd 2 Package Engineering Team, Samsung Electronics, 130, Samsung-ro, Yeongtong-gu, Suwon-si, Gyeonggi-Do, Korea, junghwa0.kim@samsung.com Abstract Molded underfill (MUF) is one of the most effective molding technologies in the advanced packaging industry. Developing highly reliable MUF is still challenging due to all basic requisitions of semiconductor packaging. Among all these requirements, controlling interfacial delamination between materials in integrated circuits (IC) packages has been considered to be the most important challenge to be achieved. Even though there are many efforts to characterize the package delamination, an effective method to speculate the delamination has not been well established. Herein, we introduce an effective and reliable evaluation method to characterize and predict the interfacial delamination and cohesive failure under mechanical and thermal stresses. The delamination temperature of moisturized package is defined at the fluctuated thermal mechanical analysis (TMA) signal point which is proportionally correlated to the delamination of real packages. Based on this result, we established the equation of package delamination with the result of package curvature by TMA and package warpage by shadow moire at 20 and 260C. The package delamination temperature can be simply calculated by using general epoxy molding compound s properties, such as global dimension change and storage modulus from TMA and dynamic mechanical analysis (DMA) respectively. The package delamination temperature calculated by the equation is well matched with the actual package delamination temperature detected by infra-red reflow method. In this paper, we will address details of theoretical backgrounds of the equation and introduce a new method for detecting the delamination temperature of packages. This novel evaluation method is able to develop and optimize a highly reliable epoxy molding compounds for MUF package. Keywords-component; Delamination failure mode; Multiple regression equation; Mechanical stress; Thermal shock; Simulation test I. INTRODUCTION The plastic encapsulants industries had only focused on the protection of Si chips from exposure to environmental conditions [1-5]. However, as electronic devices become miniaturized, integrated, and functionalized, chip makers request new functions on encapsulant which can either help the performance of electronic devices or prevent their malfunction such as high dielectric constant, electromagnetic interference, heat dissipation, heat resistance, and so on[1-2,6,7]. Among many encapsulants, epoxy molding compound () is considered to be the most reasonable encapsulation method due to their advantage on low cost, high moisture resistance, high heat resistance, and good mechanical performance. In order to add multi-functions on, organic and inorganic functional materials need to be implemented, but these new materials can influence or even govern the reliability of IC package [8]. There are a couple of parameters which can represent the chemical influences such as delamination, modability, and followability. Among many parameters, we choose to examine the package delamination because of its most prominent failure rate. The major cause of package delamination is thermal and mechanical stress at the interface between materials [11-14]. Failure behavior is interpreted by parameters closely related to those stresses. Those parameters will be evaluated by two types of methods, numerical and regression analysis which build a numerical expression from the finite elements simulations (FES). The derived equation is able to predict the failure mode of IC packages and eventually improve the reliability of packages by optimizing the elements composed. Here, we will discuss how to screen parameters to influence the package delamination and build a simulation tool based on the selected parameters. This simulation tool will be compared with the experimental result. II. RSULTS AND DISSCUSION A. Method I In order to evaluate the delamination behavior, six different s from (I) to (VI) were prepared with various resin systems and filler contents. All components such as PCB, die (8.92x10.81 mm), and Sn-Ag bump for a emuf packaging were prepared and molded under the standard package procedures. All prepared IC packages underwent the post mold cure step at 175 C for 4 hours, a /17 $ IEEE DOI /ECTC

2 baking step at 120 C for 24 hours, and then the moisture soaking process at 85 C and 85% RH for 24 hours. Furthermore, these IC packages underwent the thermal stress process which was preset at the specific temperature and time in Figure 1. Six different experiments were conducted under the different temperature condition in Table 1. This condition of thermal stress was well controlled by thermal profiler and monitored by the shadow moire laser based imaging technique. Then, any package failure or cracks inside the package were investigated by scanning acoustic tomography (SAT) before and after the experiments. TABLE 2. PACKAGE DELAMINATION VIA SAT Temp ( C) C C C (I) (II) (III) (IV) (V) (VI) C C C FIGURE 1. THERMAL STRESS CONDITION TABLE 1. IN THERMAL STRESS CONDITION No Temp. by thermal profiler( C) Time (sec) To characterize the delamination behavior of these packages, many elements possibly influencing the delamination were studied and tested by many analytical methods. Among these analytical trials, TMA, DMA, and shadow moire analysis were chosen because of their wide use in the field of analysis. B. Method II Detecting the delamination via method 1 shows very accurate and reliable results in terms of mimicking the delamination. However, this method needs too much effort and materials to perform the experiment. Therefore, we need to develop a simpler tool to evaluate the delamination. Firstly, dimension changes from TMA were evaluated to establish a relationship with the critical temperatures. As shown in Figure 2, the MUF package was set up and its behavior was monitored via TMA under the temperature range of C and ramp-up speed of 20 C /min. In the case of (I), any package crack or delamination was not detected until the condition of thermal stress reached to 298 C in 300 seconds. Then, a delamintion was first observed under the condition at the temperature of 303 C in 300 second. This temperature was determined as a critical temperature. Similarly, the experiments on (II), (III), (IV), (V), and (VI) were performed under the previously programmed thermal stress conditions in Table1. The critical temperatures of respective s were determined as 298, 293, 283, 288, and 313 C respectively. 1154

3 FIGURE 2. EXPERIMENTAL SET UP IN TMA The dimension of packages was expanded as the temperature rising shown in Figure 3. A sudden dimensional change was observed at a certain point which indicates the interfacial delamination of package. In order to obtain a relationship between the dimensional change of IC packages and those critical temperatures, we prevent the delamination of packages by eliminating a socking process. As a result, we could obtain the dimension of respective packages at the delamination point in Figure 5. With these data in hand, the graph of dimension behavior was plotted according to the temperature change in Figure 4. Unfortunately, all of critical temperatures in Figure 5 were not elucidated by the dimensional change itself. FIGUER 5. GLOBAL DIMENSION CHANGE AT THE CRITICAL Similarly, the warpage data were collected from shadow moire. We have tried to manipulate those data to obtain a relationship with critical temperatures. However, those data could not fit to any linear regression equation. Instead of using either warpage or dimension change alone, we devised many stress factors which include both warpage and global dimension change. Among all considerations, the radius of curvature was chosen best fit to the characterization of delamination behaviors. Theory behind this selection is described in Figure 6. FIGURE 3. GLOBAL DIMENSION CHANGE AT THE CRITICAL FIGURE 4. GLOBAL DIMENSION CHANGE AT THE CRITICAL FIGURE 6. PACKAGE STRESS IN TERMS OF WIDTH, HEIGHT, AND RADIUS OF CURVATURE Three different sets of 1, 2, and 3 were created by the simulation studies. Those have the different degrees of package stress. According to the internal simulation studies, 2 had the highest degree of stress level. 1 was the next and 3 had the lowest degree of 1155

4 stress level. The extent of those stresses could not be explained either by dimension change or warpage alone. In the comparison of 1 and 2, even though the dimension change of 1 and 2 are the same (W 1 =W 2 ), the degrees of stress induced by warpage from 1 and 2 are different. This phenomenon proves that dimension change alone could not explain the package stress entirely. Similarly, 1 and 3 have the same warpage, but the stresses from those are different. In this case, those warpage differences could not explain the package stresses entirely as well. Thus, we have searched for a new factor to represent the package stresses including both dimension change and warpage properties. As a result, the radius of curvature was selected to express the package stress. These phenomenons were studied and proved that the radius of curvature is the best fit to express package stress by internal simulation studies. Further, many environmental conditions was considered to use the radius of curvature. Initially, two different temperature conditions were evaluated. The first condition was the difference in temperature condition from room to high temperature (260 C). The other conditions were at high temperature (260 C). The radius of curvature according to two conditions were calculated and evaluated with critical temperature obtained from Figure 5. In order to use the change in the radius of curvature at the different temperature, numerical expression 1 was derived in terms of height and width of packages which were obtained each from warpage values through shadow moire and global dimension change through TMA respectively. As shown in Figure 7, the change in radius of curvature from room to high temperature was proportionally related to the critical temperature of package delamination. FIGURE 7. CHANGE IN RADIUS OF CURVATURE FROM 20 TO 260 VS CRITICAL TEMP. AT THE DELAMINATION() Similarly, Equation 2 to calculate the radius of curvature at high temperature (260 C) was derived in terms of height and width [15]. The change in width is relatively so small compared to that in height. The numerical expression 2 was further simplified to equation 3. Then, the calculated data was plotted based on the critical temperature. The relationship between radius of curvature at the high temperature and warpage was well agreed with the best fit line. EQUATION 2. CHANGE IN RADIUS OF CURVATURE FROM 20 TO 260 AT THE DELAMIATNION TEMP EQUATION 1. CHANGE IN RADIUS OF CURVATURE FROM 20 TO 260 AT THE DELAMIATNION TEMP. EQUATION 3. CHANGE IN RADIUS OF CURVATURE FROM 20 TO 260 AT THE DELAMIATNION TEMP With this data, we built the graph based on critical temperatures. 1156

5 soaked packages in Table 3. Additionally, the error ranges of simulated and experimented results were within 1.4%. FIGURE 8. RADIUS OF CURVATURE AT 260 VS CRITICAL TEMP () III. RSULTS AND DISSCUSION The parameters to influence delamination have been well studied [16-18]. Here, we used previously reported factors, high and low temperature modulus as well as newly adopted factor, the radius of curvature to establish the numerical expression of package delamination. As many trials of simulation, we build a numerical express to predict critical temperature in equation 4. EQUATION 4. THE PREDICTED EUQATION FOR CRITICAL TABLE 3. EXPERIMETION RESULT VS CALCULATION RESULT RT HT Radius of Critical temp ( C) No modulus (GPa) modulus (GPa) curvature (mm) Experiment result Calculation result A B C D E F Based on the data collected and calculated, the predicted interfacial delamination temperatures of MUF packages were compared experimentally with the actual delamination temperatures obtained from the TMA method. These results agreed well with the experimental data collected by TMA and shadow moire for moisture IV. CONCLUSION The actual delamination experiment via shadow moire takes too much time and effort. We developed new method to mimic the delamination. The delamination method via TMA represented the traditional method via shadow moire. With this simple tool, we have tried to develop a numerical express with various parameters such as warpage, dimension change, high temperature modulus and low temperature modulus. However, some of those parameters could not represent the critical temperature well. Therefore, we developed a new concept, the radius of curvature, which includes both warpage and dimension change. This concept was very closely related to the critical temperature. With this phenomenon, we establish the numerical expression based on the radius of curvature, high and low temperature modulus. The numerically predicted critical temperature of package delamination was experimentally validated by the delamination simulation method developed by TMA. REFERENCES 1. D. Lu, C. P. Wong. Material for Advanced Packaging Chapter 9, Springer 2017, M. Nakanish, In The latest technology of epoxy resin for electronic device II, M. Ochi, H. Kishi and T. Fukui, Editors, CMC, Tokyo, 2011, 1-3. T. Naotaka, K, Makoto, K, Tetsuo, N. Asao Evaluating ICpackaging Interface Delamination by Considering Moisture- Induced Molding-Compound Swelling Proc. International Electronics Manufacturing Technology Conference, IEEE press, Sep. 1999, pp , doi: /EPTC M. F. Sousa, O. Holck, T. Braun, J. Bauer, H. Walter, O. Wittler, K.D. Lang, Mechanically relevant chemical shrinkage of epoxy molding compounds th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems, EuroSimE 2013 IEEE press, Jun., 2013, pp. 1-6, doi: /EuroSimE B. Boehme, K. M. B. Jansen, S. Rzepka, and K.Wolter, "Thermo Mechanical Characterization of Packaging Polymers," in European Microelectronics and Packaging Conference (EMPC), 2009, pp K. M. B. Jansen, L. Wang, D. G. Yang, C. vant'hof, L. J. Ernst, H. J. L. Bressers, and G. O. Zhang, "Constitutive modeling of molding compounds," in Electronic Components and Technology Conference, 2004,pp K. M. B. Jansen, L. Wang, C. V. 'T Hof, L. J. Ernst, H. J. L. Bressers, and G. Q. Zhang, "Cure, temperature and time dependent constitutive modeling of moulding compounds," in 5th International Conference on Thermal and Mechanical Simulation and Experiments in Microelectronics and Microsystems EuroSimE 2004 no. 4,pp M. Ogata, N. Kinjo, and T. Kawata, Effects of crosslinking on physical properties of phenol-formaldehyde novolac cured epoxy resins, J. Appl.Polym. Sci., vol. 48, pp , H. E. Bair, D. J. Boyle, C. R. Taylor, S. C. Tighe, and D. L. Crouthamel, Thermomechanical properties of IC molding 1157

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