ABSTRACT: H65 Brass Alloy profiled strip for lead frame has been successfully extruded by continuous extrusion technology. In this paper, the defects (such as Burr, wave, tear, bubble, inclusion, etc.) in continuous extrusion process are analyzed and studied in detail, the reasons are found out, and the solving measures are put forward. Key words: Mechanical Manufacturing; defect; continuous extrusion; H65 brass alloy profile strip middle drawing classification number: TG376.2 document identification number: B

1. Preface

Lead frame copper strip is a special alloy material used for making semiconductor, IC lead frame and new type terminal. With the rapid development of integrated circuit industry, the requirement of lead frame materials is higher and higher, and the market demand is huge. H65 brass alloy is a good copper-based material for lead frame due to its good processing properties, mechanical properties, corrosion resistance, conductivity and heat conduction. The continuous extrusion technology is a revolutionary breakthrough in the field of Non-ferrous metal. It transforms the ineffective friction in the traditional processing field into the driving force of extrusion, and makes it become the heat source in the blank processing, the continuous extrusion of products of unlimited length soon became a new and efficient processing technique in the field of Non-ferrous metal. The technological process of producing H65 alloy profile strip by this technology is as follows: continuous extrusion —— drawing -- finishing -- cutting block. Copper Strip extrusion process is characterized by thin, wide, long, require the extruded product surface smooth, no quality defects, so that we can carry out drawing finishing, the final cut. Although continuous extrusion technology has been successfully used to extrude copper strip, there are still some defects to be overcome, such as Burr, wave pattern, tear, bubble, inclusion and so on. This article has carried on the detailed analysis and the research to these defects, has found out the reason, and proposed the solution measure.

2. Defect analysis

 2.1 burr

 2.1.1 cause analysis

The burr defect in the H65 brass alloy profile strip is that the edges of the product are serrated, as shown in figure 2. Mainly by the deformation of metal in the cavity caused by filling. As can be seen from Fig. 1, the profiled strip is very wide, which requires that the width of the deformed metal in the die cavity should be fully expanded and in full contact with the die cavity during continuous extrusion, so that the die cavity can be fully filled. However, in actual production, due to insufficient friction between the billet and the extrusion wheel groove and insufficient reduction of the compaction wheel, the billet and the extrusion wheel groove slip, resulting in deformation metal can not fully fill the cavity, resulting in Burr.

2.1.2 solution

 during continuous extrusion, the main driving force for the billet entering the die cavity is the friction between the billet and the extrusion wheel. If the driving force is small, the billet will slip with the extrusion wheel, so the extrusion friction should be large enough. Blank surface to smooth, no water, oil, dust and other impurities, to avoid skidding. Billet and extrusion wheel groove to fully contact, at the same time to increase the amount of compaction wheel, increase the Coefficient of friction. This ensures that the extrusion drive force is large enough to fill the die cavity with the deformed metal without burrs. At the same time, properly lengthen the die sizing belt length, which can increase the outlet resistance, so that the deformation of metal in the mold cavity full accumulation.

2.2 wavy lines 

2.2.1 cause analysis as can be seen in figure 3, there are wavy lines on both sides of the product. The main reason is that the flow rate of the deformed metal in both sides of the die cavity is faster than that in the middle. From Fig. 1, it can be seen that the two sides of the product are thick and the middle is thin. When the metal flows through the die cavity, the deformed metal on both sides must flow quickly, and the deformed metal in the middle must flow slowly, thus creating a continuous wave pattern. Another reason is that H65 brass compared with pure copper, its deformation resistance, poor plasticity, not easy to form. At the same time, because of the low temperature and uneven distribution in the cavity, the flow velocity of the deformed metal is inconsistent, and the metal in the high temperature area has good plasticity and flows quickly, and the metal in the low temperature area has poor plasticity and is not easy to flow.

2.2 The solution before extrusion, the cavity should be fully preheated to make its temperature uniform. On the one hand, the on-line induction heating can reduce the deformation resistance of H65 brass alloy, improve the plasticity and make the deformed metal flow uniformly in the Die Cavity; on the other hand, it can be used as a heat source to supplement the die cavity, so that the temperature can be raised. 2.3 Tear 

2.3.1 cause analysis as shown in Fig. 4, there is a tear in the thinner part of the profiled strip, which is caused by the wear of the die edge. When the deformed metal flows in the die cavity, the plastic deformation occurs, and the deformation resistance is very high. When the deformed metal passes through the die working belt, it generates strong friction on the die edge. At the same time, the deformed metal will have impact on the die, after a period of extrusion, there will be zigzag wear and tear. Because the deformation metal speed is not consistent, the flow of metal in the middle of the mold resistance than the two sides, so, the mold middle wear is very severe, there is a saw-tooth damage.

2.3.2 the solution is shown in Fig. 5B by rounding the corners of the die edges to reduce resistance and friction to the deformed metal. Preheat the billet, reduce the deformation resistance, improve the plasticity, so that it is easy to flow.

2.4 bubbles

 2.4.1 analysis of the causes of gas bubbles is mainly gas into the product, some bubbles continuous distribution, some are a single large bubble, as shown in figure 6. The first reason is the gas from the alloy, especially the gas hole in the billet, the gas in the hole in the continuous extrusion process into the product to form bubbles. Secondly, the surface of the alloy rod is oxidized to form Cu CO3g Cu (OH)2[4] in the process of waiting extrusion, and the gas is decomposed to form bubbles in the process of continuous extrusion under high temperature and high pressure. There is alloy rod surface sticky oil, dust, moisture and so on. The third is the continuous extrusion process in which air is brought in, and the formation of bubbles.

2.4.2 measures to strictly control the gas content of raw materials. Protect the raw material from oxidation and dirt such as dust, water, oil, paint, etc. . Third, properly adjust the gap between the extrusion wheel and the cavity, so that the relative gap is appropriate. Adjust the deformed block to prevent air leakage. 2.5 inclusion 

2.5.1 cause analysis the black spot in Fig. 7 is an inclusion. If there is an inclusion, it will break at the inclusion during the subsequent drawing process. The oxide impurity in the raw material smelting exists in the extrusion blank, and the inclusion will be formed when the oxide impurity is brought into the product. Tool and die surface wear foreign body, such as extrusion wheel surface crack, peeling, wheel body surface and roller wear, falling debris into the cavity, the formation of impurities. After oxidation of the overflow material on both sides of the extrusion wheel groove and between the cavity, it is brought into the die cavity to form impurities.

2.5.2 measures to strictly control the quality of the billet, improve the production process of the billet. The clearance between the extrusion wheel and the cavity and the clearance between the scraper and the wheel are controlled to effectively remove the overflow material. Adjust the reduction of the compactor to reduce the wear of the compactor and the extrusion wheel. 

3. Conclusion 

the main defects of H65 brass alloy profiled strip in continuous extrusion process are analyzed in detail, and the causes are analyzed, and the solving measures are put forward. The H65 brass alloy profile strip was produced by continuous extrusion technology, which developed a new method to manufacture lead frame material. The method has the advantages of simple process, uniform blank, continuous production and less waste. 

Source: chinanews.com, by Li Qing

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