Radio frequency signal bonding pad optimization method based on SiP packaging

Abstract

The invention discloses a radio frequency signal bonding pad optimization method based on SiP packaging. Belongs to the technical field of radio frequency system SiP packaging, realizes introduction of structural variables to change signal transmission characteristics, improves characteristic impedance by adding a chamfer and a grounding hole at the joint of a bonding pad and a transmission line, increases return loss, reduces insertion loss and improves signal transmission characteristics. Through three-dimensional electromagnetic simulation verification, in the frequency band of 500 MHz to 20 GHz, the return loss is increased by more than 5 dB and the insertion loss is reduced by 0.5 dB compared with the traditional structure by adding the pad structure of the chamfers and the grounding holes. Along with more miniaturization, multi-functionalization and high integration of products, the requirements of the market on advanced packaging technology are continuously increased. The technology of the invention can integrate more and more radio frequency and microwave electronic equipment into a wireless communication system.

Description

Technical Field

[0001] The present invention is applied to the technical field of radio frequency system SiP packaging, and is a method for improving signal transmission characteristics by optimizing a pad to improve characteristic impedance, increase return loss and reduce insertion loss. Background Art

[0002] As electronic products and equipment become more miniaturized, multifunctional and highly integrated, the market demand for advanced packaging technology is also increasing. Using System in Package technology, more and more RF and microwave electronic devices can be integrated into wireless communication systems. According to the definition of the International Technology Roadmap for Semiconductors (ITRS), SiP is a combination of multiple active and passive devices with different functions and other devices such as MEMS or optical devices to achieve a single standard package for a certain function in a system or subsystem. It can be seen that the first factor to be considered in the packaging system is impedance matching of a certain impedance value. Impedance mismatch between circuits and RF components will cause abnormal operation of the entire RF system.

[0003] Wire bonding is an important part of the package, providing electrical connection between the leads inside and outside the integrated circuit package. The bonding wires are led out through the pads. For details, refer to Figure 1 and Figure 2 In a complex SiP package, the number of bonding pads can reach hundreds or even thousands. The transmission characteristics of the bonding pads in the signal transmission path will affect the signal transmission quality in the entire circuit and have a great impact on the insertion loss and return loss. Summary of the invention

[0004] In view of this, the present invention provides a method for optimizing a radio frequency signal pad based on SiP packaging, which improves characteristic impedance by optimizing the pad, increases return loss and reduces insertion loss to improve signal transmission characteristics.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for optimizing a radio frequency signal pad based on SiP packaging comprises the following steps:

[0007] Step 1, using 3D electromagnetic simulation software HFSS to establish a bonding pad model, and obtain a side view and a top view of the structure of the bonding pad applied to the SiP package;

[0008] Step 2: The signal line at the edge of the cavity is transitioned from the size of the microstrip structure to the size of the coplanar waveguide with ground. The problem of discontinuity in strip line size and strip line type at the connection between the microstrip structure and the coplanar waveguide with ground is solved by introducing a cut angle.

[0009] Step 3, performing three-dimensional electromagnetic simulation on the ratio of the length s of the cut angle and the width a respectively;

[0010] Step 4, performing multiple iterations of simulation on the cut angle length s and the bandwidth a to obtain the optimal values, so that the cut angle structure optimizes the return loss and the insertion loss;

[0011] Step 5, add two grounding holes outside the cut corners at the connection between the microstrip structure and the grounded coplanar waveguide, with the distances from the cut corners being ds1 and ds2;

[0012] Step 6, iteratively simulate the size and position of ds1 and ds2, and adjust the size and position of ds1 and ds2 to make the characteristic impedance at the corner close to 50 Ohm.

[0013] Step 7: Record the return loss and insertion loss values ​​after this iteration, and the optimization is completed.

[0014] Step 8: Repeat steps 3 to 6 to perform new iterations until the optimal result is reached.

[0015] Furthermore, the optimized signal line includes a connected microstrip structure and a coplanar waveguide with ground; characterized in that the microstrip structure and the coplanar waveguide with ground are transitioned by a cut angle; the cut angle defect is located at the connection end of the microstrip structure or the connection end of the coplanar waveguide with ground;

[0016] Two grounding holes are arranged on the outside of each cut-off angle, and the central axis of the grounding hole is perpendicular to the plane where the microstrip structure is located.

[0017] The beneficial effects of adopting the above optimization technical solution are:

[0018] 1. The present invention designs a transition structure for connecting a bonding pad to a transmission line that can be applied to the SiP packaging technology of a radio frequency system to meet the requirements of high-density millimeter-wave multi-input / output devices and chip connection relationships.

[0019] 2. The optimized structure designed by the present invention has the characteristics of wide bandwidth, low loss, small echo and small size. This structure reduces the echo loss and insertion loss by first improving the physical continuity of the connection and then improving the characteristic impedance continuity of the connection. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a conventional structure at the connection of signal lines.

[0021] Figure 2 It is the conventional structure of the bonding pad of the SiP package.

[0022] Figure 3 This is the optimized and improved signal line connection point of the present invention.

[0023] Figure 4 This is the structure of the optimized bonding pad of the present invention.

[0024] Figure 5 It is a schematic diagram of parameters after the cutting angle is increased according to the present invention.

[0025] Figure 6 This is the simulation result after increasing the cutting angle of the present invention.

[0026] Figure 7 It is a parameter schematic diagram after adding a grounding hole in the present invention.

[0027] Figure 8 This is the simulation result after increasing the cutting angle of the present invention. DETAILED DESCRIPTION

[0028] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0029] Reference Figures 3 to 8 , a method for optimizing a radio frequency signal pad based on SiP packaging, comprising the following steps:

[0030] Step 1: Use HFSS, a 3D electromagnetic simulation software, to build a bonding pad model and obtain the side view and top view of the bonding pad structure used in SiP packaging. In SiP packaging, RF chips generally require that the pads should maintain a characteristic impedance of 50 Ohm for access or output. In order to connect the chip and other circuits and devices, one end of the gold wire is bonded to the chip pad and the other end is bonded to the bonding pad. In order to ensure that the bonder blade can have sufficient contact with the bonding pad, a larger microstrip line structure is used, such as Figure 1 and Figure 2 As shown;

[0031] Step 2: At the edge of the cavity, the signal line transitions from the size of the microstrip structure to the size of the coplanar waveguide with ground, and there are discontinuities in the size and type of the strip line at the connection. This discontinuity will introduce parasitic reactance, which will cause phase and amplitude errors, mismatch between input and output, and possible parasitic coupling, which will lead to deterioration of circuit performance and affect the transmission characteristics of the current signal. In order to reduce the impact of discontinuity, the structure of the signal line connection is optimized and improved, and a cut angle is introduced at the position of the signal line connection, such as Figure 3 and Figure 4 As shown;

[0032] Step 3, introduce the cut angle, and perform three-dimensional electromagnetic simulation on the ratio of the cut angle length s and the bandwidth a, as shown in Figure 5 As shown, Figure 6 As shown in the simulation results;

[0033] Step 4, perform multiple iterations of simulation on s / a to obtain the optimal value, so that the cut-angle structure optimizes the return loss and insertion loss;

[0034] Step 5 optimizes the connection structure, but brings a new problem, which is the increase of characteristic impedance, which leads to the deterioration of echo performance. In order to improve the impedance increase at the cut corner, the characteristic impedance of the transition part is adjusted to match the specified system impedance, and two grounding holes are added at both ends of the cut corner of the connection, with the distance from the cut corner being ds1 and ds2, as shown in Figure 5. Figure 7 As shown;

[0035] Step 6, iteratively simulate the size and position of ds1 and ds2. Figure 8 As shown in the simulation results, the size and position of ds1 and ds2 are adjusted to make the characteristic impedance at the corner close to 50Ohm.

[0036] Step 7: Record the return loss and insertion loss values ​​after this iteration.

[0037] Repeat steps 3 to 6 to perform new iterations until the optimal result is reached.

[0038] The optimized signal line includes a connected microstrip structure and a coplanar waveguide with ground; the characteristic is that the microstrip structure and the coplanar waveguide with ground are transitioned by a cut angle; the cut angle defect is located at the connection end of the microstrip structure or the connection end of the coplanar waveguide with ground;

[0039] Two grounding holes are arranged on the outside of each cut-off angle, and the central axis of the grounding hole is perpendicular to the plane where the microstrip structure is located.

Claims

1. A method for optimizing radio frequency signal pads based on SiP packaging, characterized in that: The following steps are involved: Step 1, using 3D electromagnetic simulation software HFSS to establish a bonding pad model, and obtain a side view and a top view of the structure of the bonding pad applied to the SiP package; Step 2: The signal line at the edge of the cavity is transitioned from the size of the microstrip structure to the size of the coplanar waveguide with ground. The problem of discontinuity in strip line size and strip line type at the connection between the microstrip structure and the coplanar waveguide with ground is solved by introducing a cut angle. Step 3, performing three-dimensional electromagnetic simulation on the ratio of the length s of the cut angle and the width a respectively; Step 4, performing multiple iterations of simulation on the cut angle length s and the bandwidth a to obtain the optimal values, so that the cut angle structure optimizes the return loss and the insertion loss; Step 5, add two grounding holes outside the cut corners at the connection between the microstrip structure and the grounded coplanar waveguide, with the distances from the cut corners being ds1 and ds2; Step 6, iteratively simulate the size and position of ds1 and ds2, and adjust the size and position of ds1 and ds2 to make the characteristic impedance at the corner close to 50 Ohm. Step 7: Record the return loss and insertion loss values ​​after this iteration. Step 8: Repeat steps 3 to 6 to perform new iterations until the optimal result is reached.

2. The method for optimizing a radio frequency signal pad based on SiP packaging according to claim 1, characterized in that: The optimized signal line includes a connected microstrip structure and a coplanar waveguide with ground; the characteristic is that the microstrip structure and the coplanar waveguide with ground are transitioned by a cut angle; the cut angle defect is located at the connection end of the microstrip structure or the connection end of the coplanar waveguide with ground; Two grounding holes are arranged on the outside of each cut-off angle, and the central axis of the grounding hole is perpendicular to the plane where the microstrip structure is located.

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