TWI585928B - Lead frame - Google Patents

Description

Lead frame

The present invention relates to a lead frame, and more particularly to a lead frame having a silver plated surface.

The lead frame is an important component in the semiconductor process and the light-emitting diode process, and functions as a support for the outside of the wafer, and also as a circuit board for transmitting the internal functions of the electronic component to the external connection.

As shown in FIG. 9, the lead frame of the prior art comprises a metal substrate 71 and a silver plating layer 72. In the electronic packaging process, the wafer 81 is fixed on the silver plating layer 72 of the lead frame, and the wafer 81 is electrically connected to the silver plating layer 72 by a plurality of metal wires 82, thereby providing a function of transmitting electronic signals; finally, The lead frame, the wafer 81 and the plurality of metal wires 82 are covered by the package plastic 91 to protect the lead frame, the wafer 81 and the metal wire 82 from physical or chemical damage by the package plastic 91, thereby achieving packaging and protection of the integrated circuit. The purpose.

Since the silver has good conductivity, the prior art forming the silver plating layer 72 on the metal substrate 71 can help speed up the signal transmission; however, the silver plating layer 72 and the package plastic 91 still have the disadvantage of insufficient bonding force. The problem that the encapsulating plastic 91 is easily desorbed after moisture absorption is caused.

In order to meet the more severe environmental humidity resistance conditions, the prior art provides a metal surface treatment technology that roughens the surface of the metal substrate of the lead frame by etching, and then forms a plating on the roughened metal substrate. The silver layer is used to obtain a corresponding roughening treatment on the surface of the silver plating layer. Accordingly, the roughening treatment can increase the contact area between the surface of the packaged plastic and the silver plating layer, thereby improving the bonding force between the lead frame and the package plastic.

Metal surface treatment technology can try to reduce the possibility of delamination between the encapsulation layer and the lead frame; however, the roughened surface will reduce the wire bonding to the roughened metal substrate or wire bonding to the roughened plating. The bonding force of the silver layer causes the lead frame to be easily broken due to insufficient wire bonding force, and even the wafer and the external circuit are disconnected.

In view of the technical defects existing in the prior art, the object of the present invention is to improve the film structure of the lead frame, thereby improving the bonding force between the lead frame and the package plastic under the premise of taking into consideration the bonding force between the lead frame and the wire.

In order to achieve the foregoing object, the present invention provides a lead frame comprising: a metal substrate; a silver plating layer formed on the metal substrate; and a silver oxide layer formed on the silver plating layer That is, the silver plating layer is formed between the metal substrate and the silver oxide layer, wherein the outer surface of the silver oxide layer has a polarity, and the thickness of the silver oxide layer is 1.3 nm or more, and the silver oxide layer is The surface potential can range from 55 mN/m to 80 mN/m.

By forming a silver oxide layer having a polarity and a suitable thickness in the lead frame, the lead frame of the present invention can not only maintain the bonding force between the lead frame and the wire, but also further improve the lead frame and the package plastic (ie, polymer polymerization). The bonding force between the materials, for example, epoxy resin, etc., thereby reducing the possibility of delamination of the lead frame and the package plastic after moisture absorption. In addition, the environmental conditions set in the encapsulation process are more conducive to taking away the water molecules physically adsorbed on the surface of the lead frame, so that the lead frame and the packaged plastic in the packaged product can have a good bonding force, thereby preventing moisture from entering the package. The product thus allows the lead frame of the present invention to pass moisture sensitization conditions in a more severe environment.

1‧‧‧ lead frame

11‧‧‧Metal substrate

21‧‧‧ Silver plating

31‧‧‧Silver oxide layer

41‧‧‧ pins

51‧‧‧ rough layer

71‧‧‧Metal substrate

72‧‧‧ Silver plating

81‧‧‧ wafer

82‧‧‧Metal wire

91‧‧‧Package plastic

A1‧‧‧ wire area

A2‧‧‧ pin area

1 is a schematic cross-sectional view of a lead frame of the present invention.

2 is a top plan view of a lead frame of the present invention.

3 is a schematic cross-sectional view of another lead frame of the present invention.

4 is a longitudinal distribution diagram of silver (3d) and oxygen (1s) elements in the lead frame obtained in Example 1.

Fig. 5 is a graph showing the depth distribution of silver (3d) and oxygen (1s) elements in the lead frame obtained in Comparative Example 1.

Fig. 6 is a graph showing the depth distribution of silver (3d) and oxygen (1s) elements in the lead frame obtained in Comparative Example 2.

Fig. 7 is a voltage-current diagram of the lead frame produced in Example 1 and Comparative Example 1.

Fig. 8 is a graph showing the reflectance of the lead frame obtained in Example 1 and Comparative Example 1.

9 is a schematic cross-sectional view showing a prior art lead frame connected to a wafer and a metal wire.

In the following, several embodiments are described to illustrate the embodiments of the present invention; those skilled in the art can easily understand the advantages and effects of the present invention through the contents of the present specification.

Referring to FIG. 1 and FIG. 2, the lead frame 1 of the present invention comprises a metal substrate 11, a silver plating layer 21 and a silver oxide layer 31. The silver plating layer 21 is formed on the metal substrate 11, and the silver oxide layer 31 is formed on Silver plated layer 21. In the lead frame 1 of the present invention, the outer surface of the silver oxide layer 31 has a polarity, and the thickness of the silver oxide layer 31 may be 1.3 nm or more and 2.5 nm or less, and the thickness of the silver plating layer 21 may be 100 nm. Above m, below 3.5 microns. In the case where the lead frame 1 has a reflectance requirement, by controlling the thickness of the silver oxide layer 31 to be 2.5 nm or less, it is possible to avoid the problem that the crystal grain becomes large due to the excessive thickness and excess of the silver oxide layer. The invention can improve the bonding force between the lead frame 1 and the package plastic while maintaining the reflectivity requirement of the lead frame 1, so that the lead frame 1 of the present invention can be applied to the field of light-emitting diodes.

In the lead frame 1 of the present invention, the composition of the silver oxide layer 31 is represented by Ag _x O _y ; specifically, the silver oxide layer 31 is a silver atom bonded to one or more oxygen atoms, and the silver oxide layer The composition of 31 includes silver oxide (AgO), silver oxide (Ag ₂ O), or a combination thereof.

In the lead frame 1 of the present invention, the thickness of the silver oxide layer 31 is preferably 1.8 nm or more and 2.5 nm or less, and the thickness of the metal substrate 11 is preferably 80 μm or more; more preferably, the silver oxide layer The thickness of 31 is 2 nm or more and 2.5 nm or less. Here, it should be understood that the upper limit of the thickness of the metal substrate 11 is not particularly limited, and those skilled in the art can adjust it according to its cost or demand considerations.

Referring to FIG. 3, in an embodiment of the present invention, a roughening layer 51 is further disposed between the metal substrate 11 and the silver plating layer 21, and the silver plating layer 21 is formed on the silver oxide layer 31 and roughened. Between layers 51. The roughening layer 51 may be a copper plating layer or a nickel plating layer, but is not limited thereto.

In order to improve the bonding force between the lead frame 1 and the package plastic, in the manufacturing process of the lead frame 1 of the present invention, the metal substrate 11 on which the silver plating layer 21 is formed is used as a cathode, and the insoluble electrode is an anode, an alkaline solution. The electrolyte solution is subjected to an electrochemical reaction by direct current, whereby the silver oxide layer 31 is formed on the surface of the silver plating layer 21. In an embodiment of the invention, the insoluble electrode is a platinum-coated titanium electrode or an iridium-coated titanium electrode.

In another embodiment of the present invention, an outer surface of the silver oxide layer 31 is further formed with an anti-silver gel diffusion layer which is cured by an anti-silver gel diffusion agent formed on the silver oxide layer 31. The anti-silver gel diffusion reagents applicable to the present invention are, for example, commercially available T13 (available from Atotech) and commercially available BA-9 (purchased from Nippon Mining & Metals Co., Ltd.). .Ltd.)) or a fluorine-containing organic compound (Bestguard No. 4, available from Chemitech), but is not limited thereto.

In the lead frame 1 of the present invention, the surface of the silver oxide layer 31 may have an oxygen content of between 20% and 70%. Further, the surface energy of the silver oxide layer 31 may be between 55 mN/m and 80 mN/m. When the surface energy of the silver oxide layer in the lead frame is lower than 55 mN/m, the polarity of the surface is low, and the bonding force between the lead frame and the package plastic cannot be specifically improved, so that the lead frame is difficult to be specifically applied to high-order products ( For example: in automotive electronic components); in contrast, when the surface potential of the silver oxide layer in the leadframe exceeds At 80 mN/m, the crystal grain of the silver oxide layer becomes large, which in turn increases the irregularity of the surface of the silver oxide layer, and even reduces the bonding force of the wire bonding and the solid crystal thrust, which affects the reliability of the electronic product.

Hereinafter, several embodiments and comparative examples will be described to illustrate the advantages and effects of the lead frame of the present invention, but are not intended to limit the scope of the present invention.

Example 1

The lead frame 1 of the present embodiment is obtained by the following method: First, a metal substrate 11 having a size of 19 mm × 19 mm × 0.254 mm is prepared, and the material of the metal substrate 11 is a copper alloy (C194).

Next, after the metal substrate 11 is degreased with an alkaline degreaser, the metal substrate 11 is used as a cathode, the silver plate is used as an anode, and silver cyanide is used as an electrolyte, and a direct current of 2 amps/dm 2 is passed through the metal substrate. A silver plating layer 21 is formed on the surface of 11 to obtain a silver-plated carrier.

Thereafter, the silver-plated carrier is immersed in an alkaline solution at 45 ° C, and the silver-plated carrier is used as a cathode, and the titanium-plated platinum electrode is used as an anode, and a DC current having a current density of 12 amps/dm 2 is applied for 45 seconds. A silver oxide layer 31 is formed on the surface of the silver plating layer 21 to obtain a lead frame 1 having a suitable polarity silver oxide layer 31.

Referring to FIG. 1 and FIG. 2 together, the lead frame 1 obtained by the above method has a metal substrate 11, a silver plating layer 21 and a silver oxide layer 31. The silver plating layer 21 is formed on the metal substrate 11 and oxidized. The silver layer 31 is formed on the silver plating layer 21 formed between the metal substrate 11 and the silver oxide layer 31, and the silver oxide layer 31 is bonded by oxygen atoms, so that the silver oxide layer 31 can be formed. The outer surface has a large polarity. According to the analysis result of the film thickness meter, the thickness of the silver plating layer 21 in the lead frame 1 was 2 μm.

Example 2

In addition to the lead frame described in the foregoing embodiment 1, the present specification further provides an embodiment of the second lead frame. The manufacturing method of the lead frame of Embodiment 2 is substantially the same as the manufacturing method of the lead frame of Embodiment 1. The difference is that the length of time for energization treatment is controlled to form silver plating layers of different thicknesses on the metal substrate.

As shown in FIG. 1 and FIG. 2, the lead frame of Embodiment 2 also has a metal substrate 11, a silver plating layer 21, and a silver oxide layer 31. The silver plating layer 21 is formed on the metal substrate 11, and the silver oxide layer 31 is formed on On the silver plating layer 21, the silver plating layer 21 is formed between the metal substrate 11 and the silver oxide layer 31, and the silver oxide layer 31 contains oxygen atoms, so that the outer surface of the silver oxide layer 31 has a polarity. According to the analysis result of the film thickness meter, the thickness of the silver plating layer 21 in the lead frame was 2.5 μm.

Comparative Example 1

In the preparation method of the lead frame of the comparative example, a metal substrate as used in the first embodiment is also prepared, and then the metal substrate is degreased with an alkaline degreaser, and the metal substrate is used as a cathode, and the silver plate is an anode and cyanide. The silver potassium is used as an electrolyte, and a direct current of 2 amps/dm 2 is passed, and a silver plating layer is formed on the surface of the metal substrate to complete the fabrication of the lead frame.

Through the foregoing preparation method, the lead frame prepared in Comparative Example 1 contained only the metal substrate and the silver plating layer. According to the analysis results of the film thickness meter, the thickness of the silver plating layer in the lead frame of Comparative Example 1 was about 2 μm.

Comparative Example 2

The manufacturing method of the lead frame of the comparative example is substantially the same as that of the lead frame of the first embodiment; the difference is that the silver-plated carrier of the comparative example 2 is continuously passed through a direct current of 12 amps/square decimeter. After 600 seconds, a silver oxide layer was formed on the surface of the silver plating layer to obtain a lead frame of Comparative Example 2.

Comparative Example 3

The lead frame of this comparative example was substantially the same as the lead frame of Comparative Example 1, that is, the lead frame prepared in Comparative Example 3 contained only the metal substrate and the silver plating layer. According to the analysis results of the film thickness meter, in the lead frame of Comparative Example 3, the thickness of the silver plating layer was about 2.5 μm.

Test Example 1: Thickness of silver oxide layer and surface oxygen content

In order to verify whether or not a silver oxide layer is formed in the lead frame and confirm its characteristics, this test example was measured by electron spectroscopy for chemical analysis (ESCA), respectively, in Example 1, Comparative Example 1, and Comparative Example 2. The depth distribution map of the silver element (3d) and the oxygen element (1s) in the lead frame is used to obtain the thickness of the silver oxide layer and the oxygen content on the surface thereof, and the results are shown in Figs. 4 to 6, respectively.

As shown in Fig. 4, the lead frame of Example 1 had a surface oxygen content of 30% and an oxygen element depth of about 2 nm. From this, it was found that in the lead frame of Example 1, the thickness of the silver oxide layer was about 2 nm. Further, in the present embodiment, the thickness of the silver oxide layer in the lead frame obtained in Example 2 was measured in the same manner as above, and the thickness of the silver oxide layer in the lead frame of Example 2 was measured to be 2 nm.

In contrast, as shown in FIG. 5, the surface of the lead frame prepared in Comparative Example 1 has an oxygen content of only 10% and an oxygen element depth of about 0.5 nm. Referring to FIG. 6, the surface of the lead frame prepared in Comparative Example 2 is shown. The oxygen content is about 75%, and the oxygen element depth is about 4 nm.

In addition, in this experiment, silver/silver chloride was used as the reference electrode, and the lead frame of Example 1 and Comparative Example 1 was subjected to cyclic voltammetry scanning in the potential range of 0.25V to 0.6V. Shown. The results of the combination of FIG. 4 and FIG. 7 confirm that the formation of the peak can be observed from the voltage-current diagram of the first embodiment, and that the surface of the lead frame of the first embodiment is indeed oxidized and formed appropriately. The thickness of the silver oxide layer; in contrast, the results of FIG. 5 and FIG. 7 show that the voltage-current diagram of the silver-plated carrier does not show a significant peak in the preparation method of the comparative example 1, and the comparative example is shown. 1 No obvious oxidation phenomenon occurs, that is, there is no substantial silver oxide layer in the lead frame.

It can be seen from the experimental results of the above-mentioned Embodiment 1, Comparative Example 1 and Comparative Example 2 that the formation of the silver oxide layer in the lead frame can be ensured by energizing the metal substrate; and the direct current is controlled by controlling the silver-plated carrier. Time, it can effectively control the thickness of the silver oxide layer in the lead frame falling between 1.3 nm and 2.5 nm, and the surface oxygen content is controlled between 20% and 70% to ensure the application of the lead frame. .

Test Example 2: Surface potential energy

In this test example, the surface potential of the lead frame obtained in Example 1 and Comparative Example 1 was measured by the Owen-Wendt-Rabel-Kaelble method. According to the experimental results, the surface potential of the lead frame of Example 1 was 73.32 mN/m, and the surface position of the lead frame of Comparative Example 1 was 47.51 mN/m.

It was confirmed by the result that the surface potential of the lead frame of Example 1 was larger than that of the lead frame of Comparative Example 1. The surface of the lead frame of Example 1 was surely formed with a silver oxide layer, and the silver oxide layer was provided. , can make the outer surface of the lead frame have a greater polarity.

Test Example 3: Bonding force between lead frame and gold wire

This test example is also based on the US military standard -833 (United States Military Standard-833, MIL-STD-883) measurement specification, using a gold wire with a wire diameter of 1.2 mils, respectively, the gold wire is welded in the embodiment 1 and the lead frame of Comparative Example 1 were subjected to a gold wire tensile test.

According to the experimental results, the bonding strength of the lead frame of Example 1 to the gold wire was 5.05 N, and the bonding strength of the lead frame of the comparative example 1 to the gold wire was 4.29 N. From the comparison results of the first embodiment and the comparative example 1, it can be seen that the formation of a silver oxide layer on the silver plating layer in the lead frame not only reduces the bonding force between the lead frame and the gold wire, but also improves the lead frame and The effect of the bonding force between the gold wires, thereby reducing the possibility of an open circuit in the integrated circuit.

Test Example 4: Bonding force between lead frame and package plastic

This test example is based on the measurement standard of semiconductor standard G69-0996 (Semiconductor Standard G69-0996, SEMI-G69-0996), and the epoxy resin (purchased from Changxing Material Industry Co., Ltd., EK5600GHR) is respectively adhered to the embodiment. 1 and the lead frame prepared in Comparative Example 1, and using a shear method, the curing temperature of the epoxy resin was 175 ° C, and the curing time was 6 hours to evaluate the between the lead frame and the package plastic. Bond strength. According to the experimental results, the bonding strength between the lead frame of Example 1 and the package plastic was 1.326 N, and the bonding strength between the lead frame of Comparative Example 1 and the package plastic was 0.779 N.

From the comparison results of the first embodiment and the comparative example 1, it can be seen that the strength of the bonding force between the lead frame of the first embodiment and the package plastic can be specifically improved by forming a silver oxide layer of a proper thickness on the silver plating layer in the lead frame. It allows it to pass moisture-sensitive conditions in harsher environments.

Test Example 5: Environmental moisture sensitivity test

In this test example, the lead frame prepared in Example 2 and Comparative Example 3 was used as a sample to be tested, and the environmental moisture tolerance test was performed according to the test method described below, thereby comparing Example 2 and Comparative Example 3 The delamination of the lead frame at the wire area and the pin area respectively.

Referring to FIG. 2, the lead frame 1 of the embodiment 2 and the comparative example 3 can be divided into a wire area A1 and a pin area A2. The pin area A2 includes a plurality of pins 41, and the pins 41 are formed around. Around the wire area A1. Referring to FIG. 1 and FIG. 2, in the lead frame of Embodiment 2, the silver oxide layer 31 is simultaneously formed on the wire area A1 and the pin area A2. In order to ensure the experimental significance, Example 2 and Comparative Example 3 are lead frames of the same size, and both have the same wire area and pin area of the same area; the difference of the lead frames of Embodiment 2 and Comparative Example 3 mainly lies in plating. Whether a silver oxide layer of a suitable thickness is formed on the silver layer.

First, the mold was pre-baked at 175 ° C for 4 hours; the lead frame was placed in a mold and allowed to stand at 850 ° C and 85% relative humidity for 168 hours; after a series of reflow tests, at a maximum of 260 ° C After the test; the adhesion between the lead frames and the package plastic was measured by a Scanning Acoustic Microscope (SAM) and a strength tester to judge the lead frame of the second embodiment and the control example 3 in the lead area. The degree of delamination between the foot area and the package plastic. In this test example, the interface between the lead frame and the packaged plastic was measured by the strength tester to determine the delamination of the area if there were other signals. The degree of delamination of each lead frame is expressed by the ratio of the delamination area (ie, the delamination area of each area divided by the total area of each area). The higher the proportion of delamination area in each area, the more serious the delamination problem is. .

The experimental results show that the proportion of the area where the lead frame of the embodiment 2 is delaminated in the wire area is 0.14%, and the proportion of the area where the delamination occurs in the pin area is 0.14%; and the lead frame of the comparative example 3 is delaminated in the wire area. The area ratio is as high as 92.92%, and the proportion of the area where the delamination occurs in the pin area is 2.78%. It can be seen that the lead frame of the second embodiment has only slightly delaminated in the wire area and the pin area, but the lead frame of the control example 3 has delamination problems in the wire area and the pin area, and the wire thereof There is also a serious delamination between the silver plated layer and the packaged plastic.

Based on the results of Test Example 3 to Test Example 5, since the silver plated layer and the silver oxide layer of appropriate thickness are sequentially formed in the lead frame of Embodiment 2, the bonding force between the lead frame and the gold wire can be considered. Further, the bonding force between the lead frame and the package plastic is further improved; accordingly, the lead frame of the invention can not only balance the bonding force between the lead frame and the wire, but also improve the bonding force between the lead frame and the package plastic. This greatly reduces the problem of delamination between the lead frame and the package plastic.

Test Example 6: Reflectance test

In this test example, the reflectance of the lead frame obtained in Example 1 and Comparative Example 1 was measured by a spectrometer (KONICA MINOLTA, CM-2600d) with an error of ±0.5%, and the results are shown in Fig. 8.

As shown in FIG. 8, the reflectance curve of the lead frame obtained in Example 1 is almost the same as the reflectance curve of the lead frame produced in Comparative Example 1. As can be seen, it is formed in the lead frame of Embodiment 1. A suitable thickness of the silver oxide layer does not affect the reflectivity of the lead frame. Therefore, the lead frame of the first embodiment can solve the technical defects of the prior art and is more suitable for use in the field of light-emitting diodes.

It is apparent that the various modifications and changes can be made without departing from the spirit and novel concept of the invention, and the specific embodiments disclosed herein are not intended to limit the invention. All modifications in the scope of the appended patent application.

1‧‧‧ lead frame

11‧‧‧Metal substrate

21‧‧‧ Silver plating

31‧‧‧Silver oxide layer

Claims (11)

A lead frame comprising: a metal substrate; a silver plating layer formed on the metal substrate; and a silver oxide layer formed on the silver plating layer, and the thickness of the silver oxide layer is 1.3 Above nanometer, and the surface potential energy of the silver oxide layer is between 55 mN/m and 80 mN/m. The lead frame of claim 1, wherein the thickness of the silver oxide layer is less than 2.5 nm. The lead frame of claim 1, wherein the thickness of the silver oxide layer is 1.8 nm or more. The lead frame of claim 3, wherein the thickness of the silver oxide layer is 2 nm or more. The lead frame of claim 1, wherein the silver plating layer has a thickness of 100 nm or more. The lead frame of claim 5, wherein the silver plating layer has a thickness of 3.5 microns or less. The lead frame of claim 1, wherein the metal substrate has a thickness of 80 microns or more. The lead frame of claim 1, wherein an outer surface of the silver oxide layer is further formed with an anti-silver gel diffusion layer. The lead frame of any one of claims 1 to 8, wherein a roughened layer is further formed between the metal substrate and the silver plating layer. The lead frame of claim 9, wherein the roughened layer is a copper plating layer or a nickel plating layer. The lead frame of any one of claims 1 to 8, wherein the silver oxide layer has a surface oxygen content of from 20% to 70%.