TWI806532B - Circuit board structure - Google Patents

Abstract

A circuit board structure includes a dielectric board body and a metal via-filling structure. The dielectric board body is provided with a via, and a metal base is at the bottom of the via. The metal via-hole filling structure is on the metal base and fills the via, wherein an average misorientation angle between the surface of the metal base and the bottom of the metal via-filling structure is less than seven degrees. By controlling the average misorientation angle between the surface of the metal base and the bottom of the metal via-filling structure to be less than seven degrees, the crystal coherency between crystals can be increased, and the overall mechanical properties and electrical properties can be improved.

Description

circuit board structure

The invention relates to the field of electroplating, in particular to a circuit board structure.

With the miniaturization of microelectronic components, it is necessary to rely on high density interconnection (HDI) technology, using fine lines and a large number of stacked-via structures to interconnect printed circuit boards at different packaging levels ( printed circuit boards, PCBs).

The electroplating filler of PCB in the blind hole is often due to the change of different temperatures, such as the thermal expansion and contraction of the substrate material, the excessive difference in the coefficient of thermal expansion (CTE) between the wiring metal and the dielectric material, resulting in obvious material The thermal stress eventually causes warpage of the substrate, and even breaks the blind via.

After inspection, it can be understood that when the lattice defects between the hole-filling material and the wiring metal at the bottom increase, that is, when the degree of lattice mismatch increases significantly, the problem of a decrease in mechanical reliability and a significant increase in resistance can be observed .

In order to solve the problems faced by the prior art, a circuit board structure is provided here. The circuit board structure includes a dielectric board body and a metal filling hole structure. The body of the dielectric board is provided with a blind hole, and the bottom of the blind hole contains a metal base. The metal-filled hole structure is located on the metal base and fills the blind hole, wherein the average grain size between the surface of the metal base and the bottom of the metal-filled hole structure The grain misorientation angle is less than seven degrees.

In some embodiments, the material of the metal base and the metal filling structure is selected from the group consisting of copper, tin, silver, gold, zinc, iron, cobalt, and nickel.

In more detail, in some embodiments, the metal base is a laminated copper layer or an electroplated copper layer, and the metal hole filling structure is an electroplated copper layer.

Further, in some embodiments, an electroless copper layer is further included between the wall of the blind hole and the metal-filled via structure, and between the metal base and the metal-filled via structure, wherein the thickness of the electroless copper layer is less than 1 μm.

In more detail, in some embodiments, the metal base has a thickness of 5 to 20 μm, and the metal hole-filling structure has a thickness of 20 to 35 μm.

In some embodiments, the average grain misorientation angle between the surface of the metal pedestal and the bottom of the metal-filled via structure ranges from 1 to 5.5 degrees. In more detail, in some embodiments, the average grain misorientation angle between the surface of the metal base and the bottom of the metal-filled via structure ranges from 2 to 5 degrees.

In some embodiments, the metal-filled via structure is electroplated at a deposition rate of less than about 0.22 μm/min. In more detail, in some embodiments, the metal-filled hole structure is plated at a deposition rate of about 0.044 μm/min to 0.176 μm/min.

As described in the foregoing embodiments, by controlling the average grain misorientation angle between the surface of the metal base and the bottom of the metal-filled hole structure to be less than seven degrees, the continuity of crystals between crystals can be increased, and the overall mechanical properties and Electrical properties, while maintaining the speed of the process and the scale of mass production.

1: Circuit board structure

10: Dielectric plate body

20: blind hole

30: metal base

40: Metal hole filling structure

45: chemical copper layer

Figure 1 is a schematic cross-sectional view of a circuit board structure.

Fig. 2 is a partially enlarged view of part A of the position of the blind hole in Fig. 1 .

Fig. 3 is a detailed enlarged view of part B of the position of the blind hole in Fig. 2 .

4 is a superimposed view of a cross-sectional image of a focused ion beam (FIB) and an electron backscatter diffraction (EBSD) crystal orientation map of the metal hole-filling structure 40 and the metal base 30 .

FIG. 5 is an image quality (IQ) image of EBSD corresponding to FIG. 4 and an overlay of grain boundary analysis between electroplated copper and substrate copper.

FIG. 6 is a pulling force curve of the blind hole structure after a quick via pulling test (quick via pulling test, QVP test).

Figure 1 is a schematic cross-sectional view of a circuit board structure. Fig. 2 is a partial enlarged view of the position of the blind hole in part A in Fig. 1 . As shown in Figures 1 and 2, the circuit board structure 1 may be a multi-layer stacked structure, which may include a plurality of dielectric board bodies 10, and one or more blind holes 20 may be opened on the dielectric board body 10, The bottom of each blind hole 20 includes a metal base 30 . In addition, the circuit board structure 1 also has a metal filling hole structure 40 . The metal filling structure 40 is located on the metal base 30 and fills the blind hole 20 . Here, the metal filling structure 40 and the metal base 30 can be copper, tin, silver, gold, zinc, iron, cobalt, and nickel and other high-conductivity metals, and copper is more commonly used.

Here, the metal base 30 can be an electroplated copper layer, or a laminated copper layer, that is, the dielectric plate body 10 can be arranged on the electroplated dielectric plate body 10, through drilling, in the previous A blind hole 20 is formed on the reserved position of the electroplated copper layer, or through a pressing method The blind hole 20 is formed by pressing and bonding on the copper foil.

Fig. 3 is a detailed enlarged view of the position of the blind hole in part B in Fig. 2 . Among them, the dotted line in the figure indicates the junction between the metal hole-filling structure 40 and the metal base 30. In the experiment, the electron backscatter diffraction system (electron backscatter diffraction, EBSD) was first used to analyze the copper crystal microstructure, as shown in FIG. 3 , it can be seen that the metal base 30 and the metal filling structure 40 respectively have a plurality of crystal grains. Then use the TSL-OIM software to select the crystal grains above and below the lattice boundary, and measure the misorientation angle (θ). During the measurement, a local range of 50 μm is taken, along the bottom of the blind hole 20, that is, the lattice boundary between the metal base 30 and the metal-filled hole structure 40, and the orientation difference of the crystal grains above and below the boundary is measured sequentially at a distance of 5 μm. horn. Then average the data of 10 groups to obtain the average grain misorientation angle.

According to the misorientation angle effect, it can be understood that the grain misorientation angle is proportional to the resistivity, and the resistivity can be calculated according to the following equation (1), ie (Mayadas-Shatzkes model). In the structure to be controlled in this case, considering mechanical properties, electrical properties and process speed, the average grain misorientation angle is less than seven degrees. Preferably, the average grain misorientation angle ranges from 1 to 5.5 degrees, further, the average grain misorientation angle ranges from 2 to 5 degrees.

where ρ _gb is the grain boundary resistivity (μΩ cm), ρ _b is the bulk resistivity (μΩ cm), r is the grain boundary reflection coefficient (grain boundary reflection coefficient), λ is Electron mean free path (nm), D is the grain size (grain size) (μm).

Referring again to FIG. 2 , the blind hole 20 is trapezoidal, with a bottom width of 50 μm, an upper width of 60 μm, and a depth of 27 μm. However, this is only an example and not limited thereto. If the width of the bottom of the blind hole 20 is wider, the number of sampling points can be increased to increase the reliability of the average value when measuring the grain misorientation angle.

In order to increase the adhesion before electroplating, the electroless copper layer 45 can be formed by wetting and electroless plating before electroplating to form the metal filling hole structure 40. In other words, after the electroplating is completed, the electroless copper layer 45 is located in the hole of the blind hole 20 Between the wall and the metal filling structure 40, and between the metal base 30 and the metal filling structure 40, the thickness of the chemical copper layer 45 is less than 1 μm, preferably, the thickness is in the range of 0.5 μm to 0.8 μm, such as 0.7 μm . In addition, the metal base 30 has a thickness of 5 to 20 μm, and the metal filling structure 40 has a thickness of 20 to 35 μm, for example, 26 μm.

In more detail, because the thickness of the chemical copper layer 45 is relatively thin, during the pickling before electroplating, the chemical copper layer 45 part will be etched and partially removed, so the thickness of the chemical copper layer 45 can be ignored during measurement, and the average crystal grain The measurement of the misorientation angle can be regarded as the average grain misorientation angle between the metal base 30 and the metal-filled via structure 40 .

The misorientation angle can be controlled by controlling the deposition rate of electroplating through experiments. It is found that when the deposition rate decreases, a lower average misorientation angle can be obtained to achieve better electrical properties. and mechanical properties. However, there is a side effect of reducing yield and process speed. Considering both, the deposition rate is selected to be less than 0.22 μm/min, preferably, the deposition rate is generally controlled to be 0.044 to 0.176 μm/min. As a reference value, the deposition rate generally used in the industry is 0.22 to 0.44 μm/min.

The method of the experiment will be described in detail below. The following uses the double-layer dielectric board body 10 to carry out various measurements on the metal base 30 and the metal filling structure 40 in the upper blind hole 20. Here, the metal base 30 is pressed copper, the width of the bottom of the blind hole 20 is 50 μm, the width of the upper part is 60 μm, and the depth is 27 μm. The thickness of the metal base 30 is about 20 μm, and the thickness of the metal filling structure 40 is about 26 μm. The measurement of the average grain misorientation angle, the measurement of the electrical resistance, and the tensile test were carried out according to the foregoing.

The following is through different examples, wherein the comparative example is to electroplate the metal filling structure 40 at a deposition rate of 0.44 μm/min, and the experimental example 1 is to electroplate the metal filling structure 40 at a deposition rate of 0.22 μm/min, and the experimental example 2 is The metal-filled hole structure 40 was electroplated at a deposition rate of 0.11 μm/min. In Experimental Example 3, the metal-filled hole structure 40 was electroplated at a deposition rate of 0.066 μm/min. The experimental results obtained are shown in Table 1.

Among them, in the actual experiment, the cross-sectional image of the focused ion beam (FIB) and the EBSD crystal orientation map of the metal filling structure 40 and the metal base 30 are superimposed, and the image definition of the EBSD is used to analyze the IQ image and the electroplating Please refer to Figure 4 to Figure 6 for the grain boundary analysis stack between copper and substrate copper, and the pulling force curve of the blind via structure after the quick via pulling test (QVP test). where the dotted line in Figure 4 represents the metal The interface between the filling structure 40 and the metal base 30 , FIG. 5 corresponds to FIG. 4 . Figure 6 is (25×24BHs).

By comparing the results of the above experiments, taking a comprehensive look at the results of the measurement of the average grain misorientation angle, the measurement of the resistance, and the results of the tensile test, the output of the process, and the process rate, a lower deposition rate is selected to control the metal base. The average grain misorientation angle between the surface and the bottom of the metal-filled via structure is less than seven degrees.

In summary, as described in the foregoing embodiments, the average grain misorientation angle between the surface of the metal base 30 and the bottom of the metal filling structure 40 is less than seven degrees, which can increase the continuity of crystals between crystals and improve the overall Excellent mechanical characteristics and electrical properties, while maintaining the speed of the process and the scale of mass production.

Although the technical content of the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any modification and modification made by those skilled in the art without departing from the spirit of the present invention should be covered by the present invention. Therefore, the scope of protection of the present invention should be defined by the scope of the appended patent application.

20: blind hole

30: metal base

40: Metal hole filling structure

45: chemical copper layer

Claims (9)

A circuit board structure comprising: A dielectric plate body is provided with a blind hole, and the bottom of the blind hole includes a metal base; and a metal hole-filling structure is located on the metal base and fills the blind hole, wherein the surface of the metal base and the An average grain misorientation angle between the bottoms of the metal via structure is less than seven degrees. The circuit board structure according to claim 1, wherein the material of the metal base and the metal filling structure is selected from the group consisting of copper, tin, silver, gold, zinc, iron, cobalt, and nickel. The circuit board structure according to claim 2, wherein the metal base is a laminated copper layer or an electroplated copper layer, and the metal hole filling structure is an electroplated copper layer. The circuit board structure as described in claim 3, wherein between the hole wall of the blind hole and the metal filling structure, and between the metal base and the metal filling structure, an chemical copper layer is further included, wherein the The thickness of the chemical copper layer is less than 1 μm. The circuit board structure according to claim 4, wherein the metal base has a thickness of 5 to 20 μm, and the metal hole filling structure has a thickness of 20 to 35 μm. The circuit board structure as claimed in claim 1, wherein the average grain misorientation angle between the surface of the metal base and the bottom of the metal via structure is in a range of 1 to 5.5 degrees. The circuit board structure as claimed in claim 6, wherein the average grain misorientation angle between the surface of the metal base and the bottom of the metal via structure is in a range of 2 to 5 degrees. The circuit board structure as claimed in claim 1, wherein a deposition rate of the metal-filled hole structure for electroplating is less than 0.22 μm/min. The circuit board structure as claimed in claim 8, wherein the deposition rate of the metal filling via electroplating is 0.044 to 0.176 μm/min.

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