Lead frame materials are one of the main materials used in discrete semiconductor devices and Integrated circuit packaging. There are two kinds of lead frame materials used internationally: Copper Alloy and nickel-iron Alloy, copper Alloy lead frame materials are favored for their excellent properties of high conductivity, processing, electric brazing, resistance to stress corrosion cracking, necessary strength and adhesion of resin package, etc. . At present, the domestic production of electronic lead frame with copper alloy profile copper strip, low yield, high cost, and strip length can not meet the user's continuous high-speed stamping requirements.

The special-shaped Copper Strip of copper alloy for electronic lead frame has some advantages, so it is widely used. The lead frame is the chip carrier of the Integrated Circuit. The function of the lead frame is to "connect with the external wire" . And there are many types of lead frame materials, including "KFC, C194, C7025, FeNi42, TAMAC-15, PMC-90, " and so on. The lead frame material is one of the materials used in semiconductor discrete devices and Integrated circuit packaging. The special-shaped copper strip of copper alloy for electronic lead frame has the advantages of "high conductivity, suitable workability, electric brazing, resistance to stress corrosion cracking, necessary strength and adhesion of Resin Package" , etc. , that's why it's so popular. But the cost rate of the copper alloy special-shaped Copper Strip for the electronic lead frame in our country is not high and the cost is high, so a new method is needed.

Performance of the lead frame

1. Good Electrical Conductivity: The lead frame acts as the connection between the chip and the outside of the plastic body, so it is required to have good electrical conductivity. In addition, in circuit design, the ground wire is sometimes connected to the base of the lead frame through the wall of the chip, which requires it to have good conductivity. As shown in figure 2. In order to reduce parasitic effects such as capacitance and inductance, the higher the conductivity of the lead frame, the lower the impedance of the lead frame. In general, copper has better electrical conductivity than iron-nickel. For example: Fe 58%-NI 42% FE-NI alloy, its conductivity is 3.0% iacs; cu doped with 0.1% zr, its conductivity is 90% iacs; cu doped with 2.3% fe, 0.03% P, 0.1% zn, its conductivity is 65% IACS, so it can be seen from above that, the electrical conductivity of copper is better, and the electrical conductivity is different according to different doping.

2, good thermal conductivity: Integrated Circuits in use, the total need to produce heat, especially the power consumption of the circuit, the heat generated is greater, so the main structure of the lead frame required to have a good thermal conductivity when working, otherwise in the working state will be unable to dissipate the heat in time and "burn" the chip. Thermal conductivity can be generally resolved by increasing the thickness of the lead frame substrate, the other is to choose a larger thermal conductivity of the metal lead frame. The thermal conductivity of fe-ni alloy with fe 58%-NI 42% is 15.89 w/cm ~ °C, that of cu doped with 0.1% zr is 359.8 w/cm ~ °C, and that of cu doped with 0.1% fe and 0.058% P is 435.14 w/cm ~ °C. It can be seen that the thermal conductivity of copper is the best, and the thermal conductivity is different according to the doping.

3. Good thermal fit (I. E. Thermal Expansion) : the material expands when heated. In the package, the lead frame is in contact with the plastic resin of the plastic body and also with the chip, so they are required to have a good thermal fit. The linear expansion coefficient of fe-ni alloy with fe 58%-NI 42% is 4310-7/°C. The linear expansion coefficient of lead frame made of common copper material is (160 ~ 180)10-7/°C. The expansion coefficient of the copper lead frame is similar to that of the plastic resin (about 200 ~ 10'7/C) , but quite different from that of the silicon chip. The expansion coefficient of the silicon is 26 l0-7/°C. However, the current use of resin conductive adhesive as a bonding material, they are flexible enough to absorb the stress and deformation between the chip and copper. If it is eutectic loading, then it is not appropriate to use a large coefficient of linear expansion of the steel to do the lead frame.

4. Good Strength: The lead frame is required to have good tensile strength during the packaging process, as well as during subsequent testing and during the use of the printed circuit board by the customer. The tensile strength of fe-ni alloy with fe 58%-NI 42% is 0.64 GPA, while that of cu alloy is less than 0.5 GPA, so the tensile strength of cu alloy is a little lower, and it can be improved by doping. As a lead frame, the tensile strength should reach at least 441MPA and the elongation should be more than 5% .

5.Heat resistance and oxidation resistance: heat resistance is measured by softening temperature. The softening temperature is the temperature at which the hardness of the material changes to 80% of its initial hardness after 5 minutes of heating. Usually the softening temperature above 400 °C can be used. The oxidation resistance of the material has a great influence on the reliability of the product. It is required that the oxide film formed by heating should be as little as possible.

6, with a certain degree of corrosion resistance: Lead frame should not occur stress corrosion cracking, in the general humid climate should not corrosion and leg broken phenomenon.

Traditional production technology of copper alloy special-shaped Copper Strip for lead frame

The flat ingot is heated in the atmosphere of positive pressure micro-oxidation, the heated flat Ingot is rolled several times on the hot rolling mill, and the upper and lower surfaces are milled and rolled into coils after on-line cooling. After milling, the Strip is cold rolled repeatedly on the cold rolling mill, accompanied by annealing to eliminate the cold work hardening effect. In order to improve the surface of the products, mineral oil was used as lubricating and cooling medium, and all kinds of hard strips had to be degreased before being used by users, the strip with thickness less than 0.6 m M is levelled by continuous stretch bending, both longitudinal and transverse bending can be eliminated, and the finished strip is wrapped and stored after shearing. If the product is a special-shaped tape, but also through the "shaped as electroplating" process before it can be packed into storage.

Production status of copper alloy profiled copper strip for lead frame

At present, the Copper Strip for lead frame can not be mass-produced in China, even the small amount of trial-produced products have some or other problems.

It's mainly in the way

1. More than 90% copper strip plants in China use small ingots to produce. The geometric loss is large, the rate of finished products is low, and the length of the Strip can not meet the requirements of continuous high-speed punching. In foreign countries, the long tape coil is usually used, and the rate of finished products is high. It is easy to realize high-speed and stable rolling, and the product quality is good, the efficiency is high.

2. Most factories in our country adopt the small ingot hot rolling to 4.6 mm, do not carry on the strip billet milling surface. In foreign countries, the hot-rolled strip face milling process is used in both large and small mills, which has the advantage of not only eliminating the deep subsurface defects of the Ingot, but also eliminating the surface defects caused by hot rolling, the pickling process of the INGOT milling surface and some products after hot rolling is also omitted.

3. The precision of the existing rolling and shearing equipment is very poor, there is no advanced control means, and the width and thickness deviation is quite different from that of foreign countries.

4. Although the precision of the rolling mill is very good, a few factories can not produce qualified products of high quality due to the lack of equipments such as continuous tension leveling, degreasing, precision shearing and packing.

What are the advantages of the production method of copper alloy special-shaped Copper Strip for electronic lead frame

The utility model improves the production efficiency, reduces the production cost, and the bandwidth length and the specification change at will.

Production method of copper alloy profiled Copper Strip for electronic lead frame

The process is as follows: Copper Alloy Billet → smelting → ingot casting → heating → water seal extrusion → forming → pass rolling → bright annealing → shearing.

Matters needing attention in production method of copper alloy special-shaped Copper Strip for electronic lead frame

1. The copper alloy blank is selected according to the weight percentage: Fe: 0.05 ~ 0.15% ; p: 0.015 ~ 0.04% ; Cu: excess; 

2. The heating can reach the extrusion temperature of the blank; 

3. The extrusion temperature is 850 ~ 900 °C;

 4. The bright annealing temperature is: 450 ~ 550 °C; 

5. After rolling the pass, the bright annealing process is repeated four times; 

6. The roll with "T" structure is selected for rolling the pass, a copper alloy profile copper strip with a "t" shape structure is rolled; 

7. A roll with a "U" shape structure is selected for the pass rolling, and a copper alloy profile copper strip with a "u" shape structure is rolled.

Specific case of production method of copper alloy special-shaped Copper Strip for electronic lead frame.

The copper alloy billets containing: Fe: 0.05% , p: 0.015% , Cu: excess were heated at 850 °c after the traditional melting and ingot casting process to soften the billets, in order to prevent the oxidation from extruding the softened material directly into water for water sealing, the formed copper alloy material is conveyed to the roll 2 with a "t" shape structure for pass rolling, the "T" shaped copper alloy profile copper strip rudiment 1 was rolled out. The obtained copper alloy profile copper strip rudiment 1 was annealed under the condition of 450 °C, and then the pass rolling and bright annealing processes were repeated three times, the special-shaped Copper Strip of copper alloy for electronic lead frame was obtained by shearing treatment according to the requirements, and then packed into storage.

Source: Tongxinbao

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