IMPROVEMENT OF WEAR PROBLEM AT TI DRUM EDGES AND SIMPLIFICATION OF THE SYSTEM DESIGN USING TRIMMING WHEN DRY BUFFING PROCESS Shinhoo Choi* ; Keumhwan Cha ; Youngju Kang ; Youngjun Ahn Production Engineering Center, LS Cable * shchoi@lscable.com ABSTRACT In the thin film manufacturing process such as copper foil, the process of polishing titanium drum is essential to obtain high level roughness, an even profile and stable quality of the product. However, it causes an abrading effect on the surface of the work drum, but undesired wear on drum's edges. This wear can result in serious defects (such as tearing of film, uneven electrodeposition etc.). During the manufacturing process in our factory, we actually faced this physical contradiction. Therefore, we did 'Component, Structural and Functional Analysis', and we simplified the system efficiently and concisely by applying the trimming method. Finally, we were able to derive some ideas using these inventive principles and verified those ideas by applying them. 1. INTRODUCTION The copper foil is widely used as the basic materials in semi-conductor fields. Such as PCB(Printed Circuit Board), Batteries, FPC(Flexible Printed Circuit). There are two types to produce the copper foil, the electrolytic copper foil and the rolled copper foil. However, the electrolytic type is usually preferred because of the better surficial roughness of the copper foil is a surficial roughness. The buffing process is required periodically during the manufacturing process in order to stabilize the roughness of the product. The buffing is a kind of polishing with a sandpaper brush. The roughness is controlled by the buffing process, but the harmful effect is undesirably caused as well by it. We tried to solve this kind of technical contradiction through Triz application.
Copper foil Buffing Brush Titanium Drum Dipping Roll Winder Cr coating tank Electrolytic Bath Figure 1. The process of manufacturing copper foil. 2. The description of the problem The copper foil manufacturing machine consists of titanium drum, electrolyte tank, buffing brush and guide rollers. The main functions of each part are like followings. Copper foil is electrodeposited and exfoliated on the Ti drum. Electrolytic Bath provides the drum surface with the electrolyte. Buffing brush polishes the oxidized drum surface. Guide rollers carry the copper foil after exfoliation. To sum up, manufacturing copper foil has 3 main processes of electrodeposition, exfoliation and buffing. The copper layer is electrodeposited on the tidrum by a chemical formula below. CuSO 4 + H 2 O H 2 SO 4 + Cu + 1/2 O 2 Ti drum surface is oxidized with acid mist around the machine as the foil is manufactured and wound. It causes the drum surface to be uneven(such as TiO, TiO 2 ), then affects the roughness of the product. Therefore, the buffing is required to eliminate the uneven oxidized layer and stabilize the roughness of the product. Polishing with the contact pressure Figure 2. Drum Buffing process by the brush
Acid Mist Titanium Drum Electrolytic Bath Figure 3. The oxidization of Ti drum by the acid mist There are two types of Buffing, wet and dry type. We used dry type buffing in this paper due to the excellent polishing performance. We are able to confirm it by the SEM photos of the foil. Before Buffing Shiny Side Matte Side After Buffing Figure 4. SEM photo Comparison of the copper foil s surface. From the figure 4, we can check the conditions of Shiny side detached from the drum surface and Matte side the opposite side after buffing process. Buffing process includes contacting with the abrasive, rotating and oscillating operation like other general polishing process. We faced a problem during the oscillating operation at this point. The work is a cylindrical drum surface and polished by the brush which has a longer width than the drum s one with a certain amount of oscillation rate and contact pressure. However, the drum edges are getting out of square, as it
is worn out by the brush. The O-ring(not shown in Figure) doesn t seal enough between the lug ring and the drum edge. Sealing is very important to prevent the electrodeposition at the side surface of the drum, because the residue foil at drum s sides causes foil tearing during the exfoliation. Brush Ti Drum Lug ring Figure 5. Wear of Drum s edges by the oscillating operation in the buffing process. 3. Functional Analysis Figure 6. The functional analysis of the system. The overall process comprises the foil manufacturing and drum buffing process executed over again. However, some harmful actions are included in the system functions as we see the result of the functional analysis in Figure 6. Wear action by the buffing brush is the beginning of harmful actions and the most critical factor among the harmful actions. By the way, we need to focus on the buffing brush s action here. It has a positive and negative effects simultaneously. This is the problem we have to solve here by Triz. 4. Formulation of Problem 4.1 Technical Contradictions The technical contradictions for buffing process can be defined as follows;
TC1: If the buffing brush works well, then the surface of Ti drum will be polished. Thus, the quality of the copper foil will be improved. However, the both edges of Ti drum are worn out by the buffing brush during the process. Therefore, copper particles are unevenly electrodeposited on the Ti drum and foil can be torn during the exfoliation. TC2: If the buffing brush works insufficiently, then the both edges of Ti drum will be worn out lesser. However, the irregular Ti oxide layer on Ti drum is not buffed adequately. Hence, the quality of the copper foil will be deteriorated. Figure 7. Technical Contradictions Because the quality of copper foil is more important than the drum edge abrasion, we selected technical contradiction 1. 4.2 Su-Field Modeling Fig. 2 shows Su-Field modeling. Substance S1 is Ti drum, substance S2 is buffing brush, and field F is mechanical force(friction). Buffing brush S2 buffs(useful function) surface of the Ti drum S1 during the rotation and buffing brush S2 wears(harmful function) the edges of the Ti drum S1 excessively at the same time. Figure 8. Su-Field modeling As a result, the solution of the problem could be found by three cases as follows: Harmful interaction between S1 and S2 can be removed by introducing new substance S3 between them. Harmful interaction between S1 and S2 can be removed by using modified substance S2 (buffing brush)
Harmful interaction between S1 and S2 can be removed by using modified substance S1 (Ti drum) Consequently, to solve the problem we should introduce new substance or modify the internal system. 4.3 Resource Analysis Substance Field Internal Product Ti drum rotational force System Tool buffing brush frictional force Super System lug ring, O ring, electrolyte, electric energy, chemical energy, External System Environment By-product drum shaft atmospheric air, acid mist rotational force gravity force, atmospheric pressure, chemical energy 4.4 Physical Contradiction The physical contradiction of the buffing brush and Ti drum system can be stated as follows; PC: Buffing brush must be dense and rough where it is in contact with the Ti drum surface and buffing brush should be sparse and smooth where it is in contact with the drum s edges. 5. Idea Generation 1) Introducing new substance(water) To protect Ti drum edge, the hydraulic layer such as water could be introduced. Jetting water at both sides of the Ti drum, the edge abrasion could be decreased, because the water reduces friction force between the drum surface and brush. However, the brush absorbs water gradually in this case and the water is diffused through the whole brush. Then the brush will be hardened, and buffing efficiency will be decreased. Figure 9. Idea 1(Hydraulic layer) S3: hydraulic layer
2) Introducing new substance(teflon) Teflon coated layer could be introduced to prevent the Ti drum edge abrasion. If the Teflon layer is coated on the both sides of Ti drum, the edge wear will be decreased. In addition, Teflon coated layer can prevent the copper deposition at the sides of the drum instead of O-ring and lug ring. Therefore, they can be trimmed for system simplification. Figure 10. Idea 2(Teflon coated layer) S3: Teflon layer 6. FIM for buffing system FIM means functional ideality modeling based on functional analysis above. It is usually called Trimming method because it is used to remove some component or operation in the processes. The purpose of this project is removing additional components and simplifying the technical object. There are 3 ways for trimming target component. Trimming Condition of Technical System Object A. There is no Object of the function. B. The object of the function performs this function by itself. C. The function is performed by the remaining components of TS or SS objects. O ring block Electrolyte Nonconducting Su... block Figure 11. Trimming of the technical system object To remove O-ring, we applied the Teflon coating on the drum edges, the function of O-ring is transferred to the non-conducting substance, and O- ring doesn t have any useful function. Then O-ring can be eliminated.
Motor x 2 rotate Rollers x 8 guide O ring block Electrolyte Lug Ring x 2 guide Nonconducting Su... block Figure 12. System simplification by Trimming method There are several components which does auxiliary functions to O-ring. To support and guide O-ring, rollers are used. And to rotate roller, motors are used. And 2 Lug Ring is attached to the drum to guide O-ring. These components don t have any useful function anymore, because their target component is removed. Finally this technical system is more simplified than the original system. Nonconducting Substance block deposite generate Copper Foil peel tear Front part of Ti-Drum wind 1st Roll Electrolyte abrade hold generate suck in Sub Cathode deposite Buffing Brush wear Edges of Ti-Drum hold hold Motor x 2 rotat Rollersx8 guid O ring Side part of Ti-Drum hold guide Lug Ring particles of Foil Lug Ring x 2 guid Figure 13. Functional Analysis of the simplified system by trimming method. 7. Verification of the Idea Two experiments were performed to verify the feasibility of the idea. In order to make sure the effectiveness, an Insulating tape was used to the 1 st experiment(figure 14) for the same effect as the Teflon coated layer. Titanium plate was also used instead of Ti drum. As a result of the experiment, the side electrodeposition is isolated properly from the front side by the non-conducting substance. It is shown in Figure 15. Moreover, we need to confirm whether simplification of the system is possible. Therefore, we did the 2 nd experiment about the system simplification. As we see the application result to mass-producing facility (Figure 16), we can make sure that the system can be simplified by
trimming Lug ring and O-ring and the side electrodeposition is isolated well from the front side of Ti drum during the exfoliation. Electrodes Electrolytic cell electrolyte Electric field atom Metal ion electron Figure 14. The scheme of the verification experiment Conditions 1. Ingredients of the Electrolyte Cu 80g/L + HEC + Gelatin + HCl 2. PH 2~3 3. Temperature of the Electrolyte : 50~60 C 4. Current : 25 A (5x5cm) 5. Time: 2min. 6. Estimated thickness of the foil: 30μ m Taping Edges of Ti Cathode plate Binding the Ti plate with Anode plate Electrodeposition test Figure 15. Electrodeposition experiment with Ti plate
Figure 16. Application test with the mass-producing facility 8. Conclusion After deriving ideas, we verified the feasibility and effect by using the Teflon coated layer method. In result, we were able to check the possibility of the system simplification and improvement of the edge s wear. And now we also keep verifying it in the mass-producing facility. TRIZ gives engineers chance to overview the whole process. Some contradictions in one operation seem very hard to be solved at the point, but it is possible to solve the contradiction in other operations. It widens the thinking area of engineer. This paper showed the way of approaching the practical problem using Triz. Moreover, we were able to reach the solution idea by the analyzing method. In the future, it will be applied to the mass producing line. And the optimal process condition will be defined. 8. References 1) Genrich Altshuller, 1997, 40 Principles, Technical Innovation Center. 2) Young-Ju Kang, Alexander Skuratovich, Pyeong-Kwan Chung, 2004, "TRIZ applied to Axiomatic Design, and case study; improving tensile strength of polymer insulator", ETRIA 2004 Conference Proceedings, Nov 3-5. 3) Genrich Altshuller, 1996, And Suddenly the Inventor Appeared: TRIZ, the Theory of Inventive Problem Solving, Technical Innovation Center. 4) VE+TRIZ Method for technical system improvement, LS-Cable, 2006. 5) Goldfire 2.0 workbook, TRIZ Korea, 2005. 6) Yuri Salamatov, 1999, The Right Solution at the Right Time : A Guide to Innovative Problem Solving, Insytec. B. V