A probe card structure applied to radio frequency surface acoustic wave filter wafer test

Abstract

This application discloses a probe card structure for wafer testing of radio frequency surface acoustic wave (SAW) filters, belonging to the field of semiconductor testing technology. The probe card structure includes coaxial socket spring pins, a PCB board, and a metal base plate. A straight microstrip line is laid out on the surface of the PCB board, and the solder mask layer of the PCB board reserves space at corresponding positions on the microstrip line to form solder mask windows on the microstrip line surface. Double rows of staggered shielding vias are evenly distributed within the PCB board on both sides of the microstrip line to construct an electromagnetic shielding wall. The PCB board is fixed to the metal base plate, which serves as a common ground plane. The coaxial socket spring pin is located on one side of the PCB board and electrically connected to the microstrip line. This design aims to reduce high-frequency loss of the spring pin probe card and improve electromagnetic isolation performance.

Description

Technical Field

[0001] This invention relates to the field of semiconductor testing technology, and in particular to a probe card structure for wafer testing of radio frequency surface acoustic wave filters. Background Technology

[0002] In the manufacturing process of surface acoustic wave (SAW) filters, wafer-level testing is a crucial step in ensuring product yield. Existing semiconductor testing technologies, such as the Chinese patent application publication number CN113391181A, disclose a device and wafer structure for detecting the status of wafer test probe cards. This device primarily utilizes isolated metal wires arranged around a first solder pad to determine whether the probe has penetrated the pad, thereby guiding testers to adjust the probe position in a timely manner to eliminate abnormal data.

[0003] However, these solutions primarily focus on detecting anomalies in probe contact conditions and do not address structural improvements for low-loss and high-isolation electromagnetic shielding of high-frequency radio frequency signals within the transmission channel. Existing conventional spring-loaded probe cards, when used for high-frequency testing of RF devices such as surface acoustic wave filters, suffer from limitations in their structural design. The signal transmission path within the printed circuit board (PCB) is long and often involves multiple bends, which can easily lead to RF signal reflection and loss at impedance discontinuities.

[0004] Meanwhile, these probe cards lack system-level radiation protection and inter-channel isolation barriers, causing radio frequency energy to radiate and leak outward from the microstrip line and probe root. There is signal crosstalk between the channels, which ultimately makes it difficult for the in-band ripple and isolation indicators to meet the screening standards of some radio frequency chips. The test results deviate significantly from the actual soldering test results after the device is finally packaged.

[0005] Therefore, how to reduce the RF signal loss of spring-loaded probe cards and improve their electromagnetic isolation performance has become an urgent technical problem to be solved. Summary of the Invention

[0006] The main objective of this invention is to provide a probe card structure for wafer testing of radio frequency surface acoustic wave filters, which aims to reduce the radio frequency signal loss of spring-loaded probe cards and improve their electromagnetic isolation performance.

[0007] To achieve the above objectives, this invention proposes a probe card structure for wafer testing of radio frequency surface acoustic wave (SAW) filters, comprising a coaxial socket spring pin, a PCB board, and a metal base plate. The surface of the PCB board is provided with microstrip lines for transmitting radio frequency signals, and the transmission paths of the microstrip lines are arranged in a straight line. The solder mask layer of the PCB board reserves space at the positions corresponding to the microstrip lines to form solder mask windows on the surface of the microstrip lines. Double rows of staggered shielding vias are evenly distributed within the PCB board on both sides of the microstrip lines to construct electromagnetic shielding walls on both sides of the microstrip lines. The PCB board is fixed to the metal base plate, and the metal base plate serves as a common ground plane. The coaxial socket spring pin is disposed on one side of the PCB board and is electrically connected to the microstrip lines.

[0008] Preferably, the metal base plate is a pure copper base plate.

[0009] Preferably, the probe card structure further includes an RF connector, and the microstrip line is connected to the RF connector via a soldering structure.

[0010] Preferably, the RF connector is an SMA RF coaxial connector, and the welding structure includes a first welding area and a second welding area located on the surface of the PCB board; the first welding area is used to weld to the center conductor of the SMA connector, and the second welding area is arranged around the first welding area and used to weld to the shell of the SMA connector.

[0011] Preferably, the PCB board is divided into a chip contact area for contacting the periphery of the filter chip, and a peripheral non-contact area other than the chip contact area; the PCB board has blind holes in the chip contact area, and the PCB board has staggered through holes in the peripheral non-contact area.

[0012] Preferably, the blind holes in the chip contact area are staggered around the coaxial socket spring pins.

[0013] Preferably, the diameter of the through hole in the peripheral non-pressurized area is larger than the diameter of the shielding through holes on both sides of the microstrip line.

[0014] Preferably, the double-row staggered shielding through-holes extend symmetrically and parallel to both sides of the microstrip line to form a Faraday cage shielding wall on both sides of the microstrip line.

[0015] Preferably, the coaxial socket spring pin includes a coaxial socket rigidly disposed on the surface of the PCB board, and a spring pin body movably embedded inside the coaxial socket and having an axial elastic compression stroke.

[0016] Preferably, the coaxial socket is rigidly fixed to the side surface of the PCB board facing the wafer, and the spring pin extends outward along the Z-axis direction perpendicular to the surface of the PCB board.

[0017] The above technical solution has the following beneficial effects: The probe card structure provided in this application reduces reflection and parasitic loss of high-frequency radio frequency signals in the transmission path by designing the microstrip lines on the PCB surface as a fully straight layout. By utilizing solder mask openings pre-reserved at corresponding positions on the microstrip lines, the microstrip lines are directly exposed to the surface, thereby reducing the impact of the inner layer materials and solder mask ink on the dielectric loss of high-frequency signals and ensuring the transmission quality of radio frequency signals. By symmetrically arranging double rows of staggered shielding vias on both sides of the microstrip lines in the lateral direction, a Faraday cage electromagnetic shielding wall is constructed inside the PCB, thereby suppressing the outward radiation leakage of radio frequency signals in the lateral direction, reducing interference and electromagnetic crosstalk between adjacent test channels, and improving channel isolation performance. Furthermore, fixing the PCB board to a metal base plate with conductivity and mechanical strength, and having the metal base plate provide a common ground plane for the entire test system, continuously absorbs stray signals within the system. This reduces local floating grounds and suppresses stray resonances, while improving the signal-to-noise ratio, test data reproducibility, and mechanical stability of the entire test system. Attached Figure Description

[0018] The present invention will now be described in detail with reference to specific embodiments and accompanying drawings, wherein: Figure 1 This is an exploded view of the probe card structure used for wafer testing of radio frequency surface acoustic wave filters, as provided in an embodiment of this application.

[0019] Figure 2 This is a schematic diagram of the planar design of a printed circuit board provided in an embodiment of this application.

[0020] Figure 3 This is a partially enlarged schematic diagram of the connector and microstrip line welding structure provided in an embodiment of this application.

[0021] Figure 4 This is a comparison diagram of the isolation performance between the probe card structure provided in the embodiments of this application and a regular probe card.

[0022] Explanation of reference numerals in the attached diagram: 1. PCB board; 2. Metal base plate; 3. Microstrip line; 5. Shielding via; 6. Through hole; 7. Blind via. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in detail below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other. The following embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application.

[0024] like Figure 1 As shown, Embodiment 1 provides a probe card structure for wafer testing of radio frequency surface acoustic wave (SAW) filters. This probe card structure includes a coaxial socket spring pin, a PCB board 1, and a metal base plate 2. In this embodiment, the metal base plate 2 is specifically a pure copper base plate. Pure copper material possesses conductivity and mechanical strength, which not only adapts to the size requirements of the probe station but also improves the overall mechanical strength and grounding performance of the probe card. The PCB board 1 is fixed on the metal base plate 2, and the metal base plate 2 serves as the common ground plane for the entire testing system, further absorbing stray signals and thus improving the signal-to-noise ratio of the entire testing system.

[0025] like Figure 2 As shown, microstrip lines 3 for transmitting radio frequency (RF) signals are laid out on the surface of PCB board 1. To reduce reflection and loss of high-frequency signals during transmission, the transmission path of microstrip lines 3 adopts a completely straight-line layout. Simultaneously, the solder mask layer of PCB board 1 reserves space at the corresponding positions of microstrip lines 3, thereby forming solder mask openings on the surface of microstrip lines 3. This surface-level routing design of microstrip lines 3 and the reserved solder mask openings further reduce the impact of inner layer materials and solder mask ink on the loss of microstrip lines 3, ensuring the transmission quality of RF signals.

[0026] Double rows of staggered shielding vias 5 are evenly distributed within the PCB board 1 on both sides of the microstrip line 3. These shielding vias 5 extend symmetrically and parallel to both sides of the microstrip line 3. The double rows of staggered shielding vias 5 form a Faraday cage shielding wall on both sides of the microstrip line 3. This electromagnetic shielding wall design can suppress the outward radiation leakage of radio frequency signals, reduce crosstalk between channels, and thus improve the isolation performance of the probe card.

[0027] like Figure 3 As shown, the probe card structure in this embodiment also includes an RF connector, specifically an SMA RF coaxial connector. The microstrip line 3 is connected to the SMA connector via a soldering structure to shorten the transmission distance and increase contact reliability. Specifically, the soldering structure includes a first soldering area and a second soldering area located on the surface of the PCB board 1. The first soldering area is used to solder to the center conductor of the SMA connector, and the second soldering area is arranged around the first soldering area and used to solder to the shell of the SMA connector. This soldering area layout enables a stable transition of the RF signal from the external connector to the microstrip line 3.

[0028] Furthermore, the PCB board 1 is divided into a chip contact area for contacting the outer periphery of the surface acoustic wave filter chip, and a peripheral non-contact area. Blind vias 7 are formed in the chip contact area, while staggered through-holes 6 are formed in the peripheral non-contact area. The diameter of the through-holes 6 in the peripheral non-contact area is larger than the diameter of the shielding through-holes 5 on both sides of the microstrip line 3. The blind vias 7 in the chip contact area are staggered around the coaxial socket spring pins. This regionalized hole design uses blind vias in the device contact area to avoid affecting contact, while using large-diameter staggered through-holes in non-critical areas, which enhances the overall mechanical stability of the structure and improves grounding performance.

[0029] A coaxial socket spring pin is disposed on one side of PCB board 1 and is electrically connected to microstrip line 3 for transmitting or injecting RF test signals. Specifically, the coaxial socket spring pin includes a coaxial socket rigidly disposed on the surface of PCB board 1, and a spring pin body movably embedded inside the coaxial socket and having an axial elastic compression stroke. The coaxial socket is rigidly fixed to the surface of PCB board 1 facing the filter chip wafer, while the spring pin body extends outward along the Z-axis direction perpendicular to the surface of PCB board 1. During wafer testing, the spring pin body contacts the corresponding pad on the wafer, and its axial elastic compression stroke provides stable contact pressure, reduces contact resistance, and buffers the mechanical impact during testing, ensuring test reproducibility and stability.

[0030] like Figure 1 and Figure 3 As shown, Embodiment 2 provides an implementation scheme for wafer testing of RF surface acoustic wave (SAW) filters using the aforementioned probe card structure. In specific implementation, the probe card structure is assembled and debugged at the system level to meet the requirements of low signal loss and high electromagnetic isolation. Specifically, the coaxial socket with spring pins is fixed to the wafer-facing side of the PCB board 1 using M2 screws. The microstrip line 3 is connected to the SMA connector by soldering, wherein the first soldering area is aligned with the center conductor of the SMA connector and completes the electrical signal soldering, while the second soldering area surrounds the center conductor and achieves full-circumference soldering with the metal shell of the SMA connector. This dual soldering area layout reduces the contact impedance and high-frequency parasitic inductance at the connector joint, while providing mechanical support for the microstrip line 3, preventing the frequent insertion and removal stress of the coaxial cable during testing from being directly transmitted to the interior of the PCB board 1, thereby maintaining the long-term electrical consistency of the test path.

[0031] like Figure 4 As shown, in another optional implementation scenario, the probe card structure of this application is suitable for wafer-level parallel testing of duplexers in a certain frequency band, such as screening the performance of radio frequency surface acoustic wave filter chips with frequencies of 1.980 GHz and 2.110 GHz. Figure 4In the diagram, the horizontal axis represents frequency in GHz, and the vertical axis represents isolation in dB. Dashed lines represent standard Pogo pin probe cards, while solid lines represent the probe card described in this application. Utilizing a Faraday cage electromagnetic shielding wall constructed from double rows of staggered shielding vias 5 on both sides of the microstrip line 3, the isolation of the test system is improved by 1 dB compared to a standard Pogo pin probe card at an operating frequency of 1.980 GHz; and by 3 dB between channels at an operating frequency of 2.110 GHz. The isolation on the left side at 1.980 GHz is 9 dB better than a standard Pogo pin, and the isolation on the right side at 2.110 GHz is 10 dB better than a standard Pogo pin probe card. This indicates that through the synergistic cooperation of the double-row staggered shielded through-holes 5 and the common ground plane metal base plate 2 provided in this application, the probe card can achieve performance close to that of a thin-film probe card in terms of in-band ripple, out-of-band suppression, and electromagnetic isolation, under the premise of controlled manufacturing costs. This allows the wafer-level test results to correspond with the actual test results after the final packaging of the device, thereby enabling the screening of defective structures.

[0032] As a variant of this embodiment, the spacing and diameter of the double-row staggered shielding vias 5 on both sides of the microstrip line 3 can be adaptively adjusted according to the operating wavelength of the actual RF device being tested. Specifically, the center-to-center distance of the shielding vias 5 is preferably less than or equal to 1 / 20 of the wavelength of the test signal propagating within the PCB board 1 medium, thereby forming a continuous and closed Faraday cage ground potential barrier to suppress RF energy radiation leakage laterally into adjacent channels. Simultaneously, the vias 6 opened in the non-contact area of ​​the PCB board 1 can form multi-point low-impedance grounding interconnects with the metal base plate 2, ensuring that no local floating ground is generated inside the probe card, thereby eliminating the adverse effects of stray resonance on the RF isolation index. Furthermore, the blind vias 7 in the chip contact area can be staggered around the coaxial socket spring pins, shielding the electromagnetic leakage at the probe root without compromising the mechanical integrity of the contact area.

[0033] The above description is merely a preferred embodiment of this application. Although this application has disclosed preferred embodiments above, it is not intended to limit this application. Any person skilled in the art can make many possible variations and modifications to the technical solutions of this application using the methods and techniques disclosed above, or modify them into equivalent embodiments with equivalent changes, without departing from the scope of the technical solutions of this application. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of this application without departing from the content of the technical solutions of this application shall still fall within the protection scope of the technical solutions of this application.

Claims

1. A probe card structure for wafer testing of radio frequency surface acoustic wave filters, comprising a coaxial socket spring pin, a PCB board, and a metal base plate, characterized in that, The PCB board has microstrip lines arranged on its surface for transmitting radio frequency signals, and the transmission path of the microstrip lines adopts a straight-line layout. The solder mask layer of the PCB board has reserved space at the position corresponding to the microstrip line to form a solder mask window on the surface of the microstrip line; double rows of staggered shielding vias are evenly distributed in the PCB board on both sides of the microstrip line to construct an electromagnetic shielding wall on both sides of the microstrip line; the PCB board is fixed to the metal base plate, and the metal base plate serves as a common ground plane; the coaxial socket spring pin is disposed on one side of the PCB board, and the coaxial socket spring pin is electrically connected to the microstrip line.

2. The probe card structure for wafer testing of radio frequency surface acoustic wave filters according to claim 1, characterized in that, The metal base plate is a pure copper base plate.

3. A probe card structure for wafer testing of radio frequency surface acoustic wave filters according to claim 1 or 2, characterized in that, The probe card structure also includes an RF connector, and the microstrip line is connected to the RF connector via a soldering structure.

4. The probe card structure for wafer testing of radio frequency surface acoustic wave filters according to claim 3, characterized in that, The RF connector is an SMA RF coaxial connector, and the welding structure includes a first welding area and a second welding area located on the surface of the PCB board; the first welding area is used to weld to the center conductor of the SMA connector, and the second welding area is arranged around the first welding area and used to weld to the shell of the SMA connector.

5. The probe card structure for wafer testing of radio frequency surface acoustic wave filters according to claim 1, characterized in that, The PCB board is divided into a chip contact area for contacting the filter chip and a peripheral non-contact area. The PCB board has blind holes in the chip contact area and staggered through holes in the peripheral non-contact area.

6. The probe card structure for wafer testing of radio frequency surface acoustic wave filters according to claim 5, characterized in that, The blind holes within the chip's contact area are staggered around the coaxial socket spring pins.

7. The probe card structure for wafer testing of radio frequency surface acoustic wave filters according to claim 5, characterized in that, The diameter of the through hole in the peripheral non-pressurized area is larger than the diameter of the shielding through holes on both sides of the microstrip line.

8. A probe card structure for wafer testing of radio frequency surface acoustic wave filters according to claim 1 or 2, characterized in that, The double-row staggered shielding through-holes extend symmetrically and parallel to both sides of the microstrip line to form a Faraday cage shielding wall on both sides of the microstrip line.

9. A probe card structure for wafer testing of radio frequency surface acoustic wave filters according to claim 1, characterized in that, The coaxial socket spring pin includes a coaxial socket rigidly disposed on the surface of the PCB board, and a spring pin body movably embedded inside the coaxial socket and having an axial elastic compression stroke.

10. A probe card structure for wafer testing of radio frequency surface acoustic wave filters according to claim 9, characterized in that, The coaxial socket is rigidly fixed to the side of the PCB board facing the wafer, and the spring pin extends outward along the Z-axis direction perpendicular to the surface of the PCB board.

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