A ball grid array package PCB substrate and impedance matching method thereof

Abstract

The present invention discloses a ball grid array package PCB substrate, wherein the PCB substrate comprises: an upper substrate and a lower substrate; the upper substrate comprises a microstrip line, an inner conductor, an outer conductor, a solder ball, a grounding layer, and an insulating plate, and the pad area of ​​the inner conductor is increased to 1 to 2 times of the design area; the present invention also discloses an impedance matching method for a ball grid array package PCB substrate, the method comprising the following steps: counting the average value of the assembly error of the axial centerline of the inner conductor of the upper substrate and the axial centerline of the inner conductor of the lower substrate; calculating the quasi-coaxial impedance; the calculated quasi-coaxial impedance reduces the radial size of the inner conductor of the upper substrate or / and the radial size of the inner conductor of the lower substrate, so that the quasi-coaxial impedance matches the external microwave circuit. The present invention has the characteristics of simple structure, low process requirements, and easy industrial large-scale production, and also has the characteristics of online debugging of the limiting power size; under the premise of ensuring that the standing wave (or parameter S11, or return loss) of the microwave circuit does not increase, the tolerance of the average value of the axial centerline assembly error is increased, which indirectly reduces the process difficulty of the quasi-coaxial package.

Description

Technical Field

[0001] The invention relates to a printed circuit board, in particular to a printed circuit board with a ball grid array package and an impedance matching method thereof. Background Art

[0002] Nowadays, circuit integration is getting higher and higher, SIP (system in package) technology is widely used, and vertical interconnection technology is used in the field of microwave and millimeter wave to realize signal transmission between substrates.

[0003] Microwave and millimeter wave vertical interconnection technologies include wool button technology, BGA (ball grid array packaging) technology, etc. The wool button technology is a technology that weaves gold-plated elastic metal wires in a certain way, compresses them along the axial direction, and relies on elastic contact to transmit signals; BGA (ball grid array packaging) technology is a packaging method that covers (or partially covers) pins on a certain surface in a grid-like manner, and transmits signals from one substrate to another, thereby realizing signal transmission between multiple substrates.

[0004] The PCB board (Printed Circuit Board, Chinese name is printed circuit board) using BGA technology is composed of microstrip lines, solder balls, quasi-coaxial, insulating boards, etc., among which the quasi-coaxial includes inner conductors, outer conductors, ground layers, and part of the insulating layer. Reflow soldering technology is usually used to connect multi-layer substrates using solder balls. However, when using BGA technology for system packaging, there is inevitably a certain misalignment between the axis of the conductor in the upper substrate and the axis of the conductor in the lower substrate, resulting in the two problems of reduced welding quality and impedance mismatch. The emergence of this problem is not conducive to improving the overall performance of the circuit integration system packaging. Therefore, how to improve and ensure the welding quality and achieve microwave circuit matching on the basis of improving the welding quality has become a problem that needs to be solved in the circuit integration system packaging. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a PCB substrate of a ball grid array package, the PCB substrate comprising: an upper substrate and a lower substrate;

[0006] The upper substrate comprises a microstrip line, an inner conductor, an outer conductor, a solder ball, a grounding layer, and an insulating plate. The microstrip line is attached to the surface of the insulating plate, one end of which is connected to the microstrip line, and the other end is connected to the solder ball; the outer conductor is embedded in the insulating plate, one end of which is connected to the grounding layer, and the other end is connected to the solder ball. The solder ball is welded to one end of the inner conductor and the outer conductor, and the grounding layer is embedded between the two insulating plates;

[0007] The lower substrate includes a microstrip line, an inner conductor, an outer conductor, an inner conductor pad, an outer conductor pad, a grounding layer, and an insulating plate. The microstrip line is attached to the surface of the insulating plate, one end of which is connected to the inner conductor. The inner conductor is embedded in the insulating plate, one end of which is connected to the microstrip line and the other end is connected to the inner conductor pad. The outer conductor is embedded in the insulating plate, one end of which is connected to the grounding layer and the other end is connected to the outer conductor pad. The inner conductor pad is welded to one end of the inner conductor, and the outer conductor pad is welded to one end of the outer conductor. The grounding layer is embedded between two insulating plates.

[0008] The inner conductor pad area is increased to 1 to 2 times of the designed area.

[0009] In the ball grid array package PCB substrate, the radial dimension of the inner conductor of the upper substrate of the PCB substrate is different from the overall radial dimension of the inner conductor of the lower substrate or part of the radial dimension is different.

[0010] In the ball grid array package PCB substrate, the radial size of the inner conductor and the radial size of the outer conductor of the PCB substrate are different.

[0011] In the ball grid array package PCB substrate, the radial dimension of the inner conductor part of the lower substrate of the PCB substrate is smaller than the radial dimension of the inner conductor part of the upper substrate of the PCB substrate.

[0012] In the ball grid array package PCB substrate, the overall radial dimension of the inner conductor of the lower substrate of the PCB substrate is smaller than the radial dimension of the inner conductor of the upper substrate of the PCB substrate.

[0013] In the ball grid array package PCB substrate, the radial dimension of the inner conductor of the PCB substrate is smaller than the radial dimension of the outer conductor.

[0014] The impedance matching method of a ball grid array package PCB substrate comprises the following steps:

[0015] 1) Calculate the average value of the assembly error between the axis of the conductor in the upper substrate and the axis of the conductor in the lower substrate;

[0016] 2) Calculate the quasi-coaxial impedance;

[0017] 3) According to the quasi-coaxial impedance calculated in step 2), the radial dimension of the conductor in the upper substrate or / and the radial dimension of the conductor in the lower substrate are reduced to match the quasi-coaxial impedance with the external microwave circuit.

[0018] In the impedance matching method for a ball grid array package PCB substrate, step 3) reducing the radial size of the conductor in the upper substrate or / and the radial size of the conductor in the lower substrate refers to: reducing the overall diameter of the conductor in the upper substrate or the diameter of a portion of the conductor in the upper substrate; or reducing the overall diameter of the conductor in the lower substrate or the diameter of a portion of the conductor in the lower substrate; or reducing the overall diameter of the conductor in the upper substrate and the overall diameter of the conductor in the lower substrate; or reducing the diameter of a portion of the conductor in the upper substrate and the diameter of a portion of the conductor in the lower substrate.

[0019] From a theoretical analysis, the general formula for the characteristic impedance of a coaxial transmission line is:

[0020]

[0021] In the above formula:

[0022] —Characteristic impedance, ohms

[0023] R —Internal resistance of a conductor per unit length, ohms / meter

[0024] G —Conductance of the medium per unit length, Siemens / meter

[0025] L —Inductance per unit length, henry / meter

[0026] C —Capacitance per unit length, Farad / meter

[0027] ω =2π f

[0028] f —Frequency, Hz

[0029] When R=G=0, the above formula is simplified to:

[0030]

[0031] At microwave frequencies, the internal inductance of a conductor is very small, and the inductance per unit length is very close to the external inductance per unit length:

[0032]

[0033] In the above formula:

[0034] L —External inductance per unit length, henry / meter

[0035] μ І — Magnetic permeability of the medium, henry / m

[0036] D—Inner diameter of outer conductor

[0037] d—Outer diameter of the inner conductor

[0038] The capacitance per unit length can be calculated as follows:

[0039]

[0040] In the above formula:

[0041] C —Capacitance per unit length, Farad / meter

[0042] —Dielectric constant of the medium, Farad / meter

[0043] For ordinary coaxial line

[0044]

[0045] For quasi-coaxial transmission lines, which have a similar structure to coaxial transmission lines, the above theory of coaxial transmission lines can be directly used for analysis.

[0046] When the microwave and millimeter wave substrates are used for system packaging, there is an axis line assembly error between the axis line of the conductor in the upper substrate and the axis line of the conductor in the lower substrate. , the assembly error is similar to the inner diameter of the inner conductor increasing in the misaligned position, and the inner conductor increases, the inductance Reduce, capacitance Increases, that is, the coaxial capacitance effect is enhanced (the inductive effect is weakened) and the impedance amplitude is reduced.

[0047] Increasing the inner conductor pad area and improving the quasi-coaxial welding quality will lead to further enhancement of the quasi-coaxial capacitance effect (further weakening of the inductive effect) and further reduction of the impedance amplitude.

[0048] The axis centerline assembly error and the increase of the inner conductor pad will cause the capacitance effect to increase (the inductive effect to decrease) and the impedance amplitude to decrease, resulting in impedance mismatch in the microwave circuit.

[0049] Microwave Circuit Impedance The formula is

[0050]

[0051] in is the real part of impedance (or resistance), is the imaginary impedance (or reactance), z is the impedance amplitude, is the impedance phase angle. Impedance mismatch refers to the change in the real or imaginary part of the impedance (it can also be expressed as the impedance amplitude or phase angle change). The quasi-coaxial capacitance effect is enhanced (the inductive effect is weakened) and the impedance amplitude is reduced. In order to re-match the quasi-coaxial impedance, the capacitance effect needs to be weakened (the inductive effect is enhanced) and the impedance amplitude needs to be increased. This can be achieved by reducing the radial dimensions of the inner conductors of the upper and lower substrates (the radial dimensions of a portion of the inner conductor area, or the overall radial dimensions of the upper / lower inner conductors, or the overall radial dimensions of the upper and lower inner conductors). According to the above formula, the capacitance effect is reduced (the inductive effect is enhanced) and the impedance amplitude is increased.

[0052] The present invention improves the welding quality of the upper and lower substrates by increasing the area of ​​the inner conductor pad, reducing the radial size of the inner conductor of the upper and lower substrates, and reducing the capacitance effect (weakening the inductive effect) and impedance amplitude caused by the axis centerline assembly error when the microwave and millimeter wave substrates are packaged in the system. The capacitance effect is enhanced (the inductive effect is enhanced) and the impedance amplitude is increased to improve the impedance matching between the quasi-coaxial and microwave circuits, reduce the standing wave of the microwave circuit (or parameter S11, or return loss), and re-realize the matching of the microwave circuit. The present invention has the characteristics of simple structure, low process requirements, and easy industrial large-scale production. It also has the characteristics of online debugging of the limiting power size; under the premise of ensuring that the microwave circuit standing wave (or parameter S11, or return loss) does not increase, the average value of the axis centerline assembly error is increased to The tolerance level indirectly reduces the process difficulty of coaxial packaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 Schematic diagram of the PCB substrate structure with the upper and lower substrates aligned;

[0054] Figure 2 Schematic diagram of PCB substrate structure with upper and lower substrates misaligned;

[0055] Figure 3 Schematic diagram of the structure of a PCB substrate in the embodiment; a radial dimension of a conductor portion in a lower substrate is smaller than a radial dimension of a conductor in an upper substrate;

[0056] Figure 4 Embodiment 2 A PCB substrate in which the overall radial dimension of the inner conductor of the lower substrate is smaller than the radial dimension of the inner conductor of the upper substrate;

[0057] Figure 5 Embodiment 3 A PCB substrate in which the radial dimensions of the inner conductors of the upper and lower substrates are smaller than the radial dimensions of the outer conductors.

[0058] 1. Lower substrate; 2. Upper substrate; 3. Inner conductor; 4. Outer conductor; 5. Outer conductor pad; 6. Microstrip line; 7. Solder ball; 8. Inner conductor pad. DETAILED DESCRIPTION

[0059] The technical solution of the present invention is described below with reference to the accompanying drawings and through specific embodiments:

[0060] Embodiment 1

[0061] This embodiment provides a ball grid array package printed circuit board, specifically see Figure 3 The PCB substrate comprises: an upper substrate and a lower substrate; the upper substrate comprises a microstrip line, an inner conductor, an outer conductor, a solder ball, a grounding layer, and an insulating board. The microstrip line is attached to the surface of the insulating board, one end of which is connected to the microstrip line, and the other end is connected to the solder ball; the outer conductor is embedded in the insulating board, one end of which is connected to the grounding layer, and the other end is connected to the solder ball. The solder ball is welded to one end of the inner conductor and the outer conductor, and the grounding layer is embedded between the two insulating boards; the lower substrate comprises a microstrip line, an inner conductor, an outer conductor, an inner conductor pad, an outer conductor pad, a grounding layer, and an insulating board. The microstrip line is attached to the surface of the insulating board, one end of which is connected to the inner conductor, the inner conductor is embedded in the insulating board, one end of which is connected to the microstrip line, and the other end is connected to the inner conductor pad, the outer conductor is embedded in the insulating board, one end of which is connected to the grounding layer, and another end is connected to the outer conductor pad, the inner conductor pad is welded to one end of the inner conductor, and the outer conductor pad is welded to one end of the outer conductor. The grounding layer is embedded between two insulating plates; the area of ​​the inner conductor pad is increased to 1 times the designed area.

[0062] The impedance matching method of the ball grid array package PCB substrate described in the embodiment comprises the following steps:

[0063] 1) Calculate the average value of the assembly error between the axis of the conductor in the upper substrate and the axis of the conductor in the lower substrate;

[0064] 2) Calculate the quasi-coaxial impedance;

[0065] 3) According to the quasi-coaxial impedance calculated in step 2), the radial dimension of the conductor part in the lower substrate is reduced so that the quasi-coaxial impedance matches the external microwave circuit.

[0066] Embodiment 2

[0067] This embodiment 2 provides a ball grid array package printed circuit board, specifically see Figure 4The PCB substrate comprises: an upper substrate and a lower substrate; the upper substrate comprises a microstrip line, an inner conductor, an outer conductor, a solder ball, a grounding layer, and an insulating board. The microstrip line is attached to the surface of the insulating board, one end of which is connected to the microstrip line, and the other end is connected to the solder ball; the outer conductor is embedded in the insulating board, one end of which is connected to the grounding layer, and the other end is connected to the solder ball. The solder ball is welded to one end of the inner conductor and the outer conductor, and the grounding layer is embedded between the two insulating boards; the lower substrate comprises a microstrip line, an inner conductor, an outer conductor, an inner conductor pad, an outer conductor pad, a grounding layer, and an insulating board. The microstrip line is attached to the surface of the insulating board, one end of which is connected to the inner conductor, the inner conductor is embedded in the insulating board, one end of which is connected to the microstrip line, and the other end is connected to the inner conductor pad, the outer conductor is embedded in the insulating board, one end of which is connected to the grounding layer, and another end is connected to the outer conductor pad, the inner conductor pad is welded to one end of the inner conductor, and the outer conductor pad is welded to one end of the outer conductor. The grounding layer is embedded between two insulating plates; the area of ​​the inner conductor pad is increased to 1.5 times the designed area.

[0068] The impedance matching method of the ball grid array package PCB substrate described in the embodiment comprises the following steps:

[0069] 1) Calculate the average value of the assembly error between the axis of the conductor in the upper substrate and the axis of the conductor in the lower substrate;

[0070] 2) Calculate the quasi-coaxial impedance;

[0071] 3) According to the quasi-coaxial impedance calculated in step 2), the overall radial dimension of the conductor in the lower substrate is reduced so that the quasi-coaxial impedance matches the external microwave circuit.

[0072] Embodiment 3

[0073] This embodiment 3 provides a ball grid array package printed circuit board, specifically see Figure 4The PCB substrate comprises: an upper substrate and a lower substrate; the upper substrate comprises a microstrip line, an inner conductor, an outer conductor, a solder ball, a grounding layer, and an insulating board. The microstrip line is attached to the surface of the insulating board, one end of which is connected to the microstrip line, and the other end is connected to the solder ball; the outer conductor is embedded in the insulating board, one end of which is connected to the grounding layer, and the other end is connected to the solder ball. The solder ball is welded to one end of the inner conductor and the outer conductor, and the grounding layer is embedded between the two insulating boards; the lower substrate comprises a microstrip line, an inner conductor, an outer conductor, an inner conductor pad, an outer conductor pad, a grounding layer, and an insulating board. The microstrip line is attached to the surface of the insulating board, one end of which is connected to the inner conductor, the inner conductor is embedded in the insulating board, one end of which is connected to the microstrip line, and the other end is connected to the inner conductor pad, the outer conductor is embedded in the insulating board, one end of which is connected to the grounding layer, and another end is connected to the outer conductor pad, the inner conductor pad is welded to one end of the inner conductor, and the outer conductor pad is welded to one end of the outer conductor. The grounding layer is embedded between two insulating plates; the area of ​​the inner conductor pad is increased to twice the designed area.

[0074] The impedance matching method of the ball grid array package PCB substrate described in the embodiment comprises the following steps:

[0075] 1) Calculate the average value of the assembly error between the axis of the conductor in the upper substrate and the axis of the conductor in the lower substrate;

[0076] 2) Calculate the quasi-coaxial impedance;

[0077] 3) According to the quasi-coaxial impedance calculated in step 2), the radial dimension of the conductor inside the PCB substrate is reduced to match the quasi-coaxial impedance with the external microwave circuit.

[0078] The embodiment of the present invention improves the welding quality of the upper and lower substrates by increasing the area of ​​the inner conductor pad, reducing the radial size of the inner conductors of the upper and lower substrates, and reducing the capacitance effect (weakening the inductive effect) and impedance amplitude caused by the axis centerline assembly error when the microwave and millimeter wave substrates are packaged in the system. The capacitance effect is enhanced (the inductive effect is enhanced) and the impedance amplitude is increased to improve the impedance matching between the quasi-coaxial and microwave circuits, reduce the standing wave of the microwave circuit (or parameter S11, or return loss), and re-realize the matching of the microwave circuit. The present invention has the characteristics of simple structure, low process requirements, and easy to realize industrial large-scale production. It also has the characteristics of online debugging of the limiting power size; under the premise of ensuring that the standing wave of the microwave circuit (or parameter S11, or return loss) does not increase, the average value of the axis centerline assembly error is increased to The tolerance level indirectly reduces the process difficulty of coaxial packaging.

[0079] The above embodiments merely illustrate the basic principles and characteristics of the present invention. The present invention is not limited by the above embodiments. Without departing from the spirit and scope of the present invention, the present invention may undergo various changes and modifications. These changes and modifications all fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the scope of the claims combined with the scope of the specification.

Claims

1. A ball grid array package PCB substrate, characterized in that: The PCB substrate comprises: an upper substrate and a lower substrate; The upper substrate comprises a microstrip line, an inner conductor, an outer conductor, a solder ball, a grounding layer, and an insulating plate. The microstrip line is attached to the surface of the insulating plate, one end of which is connected to the microstrip line, and the other end is connected to the solder ball; the outer conductor is embedded in the insulating plate, one end of which is connected to the grounding layer, and the other end is connected to the solder ball. The solder ball is welded to one end of the inner conductor and the outer conductor, and the grounding layer is embedded between the two insulating plates; The lower substrate comprises a microstrip line, an inner conductor, an outer conductor, an inner conductor pad, an outer conductor pad, a grounding layer, and an insulating plate. The microstrip line is attached to the surface of the insulating plate, one end of which is connected to the inner conductor. The inner conductor is embedded in the insulating plate, one end of which is connected to the microstrip line and the other end is connected to the inner conductor pad. The outer conductor is embedded in the insulating plate, one end of which is connected to the grounding layer and the other end is connected to the outer conductor pad. The inner conductor pad is welded to one end of the inner conductor, and the outer conductor pad is welded to one end of the outer conductor. The grounding layer is embedded between two insulating plates; The inner conductor pad area is increased to 1 to 2 times the designed area; The radial dimension of the inner conductor of the upper substrate of the PCB substrate is different from the overall radial dimension of the inner conductor of the lower substrate or part of the radial dimension is different; The radial size of the inner conductor and the radial size of the outer conductor of the PCB substrate are different.

2. A ball grid array package PCB substrate as claimed in claim 1, characterized in that: The radial dimension of the inner conductor portion of the lower substrate of the PCB substrate is smaller than the radial dimension of the inner conductor portion of the upper substrate of the PCB substrate.

3. A ball grid array package PCB substrate as claimed in claim 1, characterized in that: The overall radial dimension of the inner conductor of the lower substrate of the PCB substrate is smaller than the radial dimension of the inner conductor of the upper substrate of the PCB substrate.

4. A ball grid array package PCB substrate as claimed in claim 1, characterized in that: The radial dimension of the inner conductor of the PCB substrate is smaller than the radial dimension of the outer conductor.

5. The impedance matching method of a ball grid array package PCB substrate according to claim 1, characterized in that: The method comprises the following steps: 1) Calculate the average value of the assembly error between the axis of the conductor in the upper substrate and the axis of the conductor in the lower substrate; 2) Calculate the quasi-coaxial impedance; 3) According to the quasi-coaxial impedance calculated in step 2), the radial dimension of the conductor in the upper substrate or / and the radial dimension of the conductor in the lower substrate are reduced to match the quasi-coaxial impedance with the external microwave circuit.

6. The impedance matching method of a ball grid array package PCB substrate as claimed in claim 5, characterized in that: Step 3) Reducing the radial size of the conductor in the upper substrate or / and the radial size of the conductor in the lower substrate refers to: reducing the overall diameter of the conductor in the upper substrate or the diameter of part of the conductor in the upper substrate; or reducing the overall diameter of the conductor in the lower substrate or the diameter of part of the conductor in the lower substrate; or reducing the overall diameter of the conductor in the upper substrate and the overall diameter of the conductor in the lower substrate; or reducing the diameter of part of the conductor in the upper substrate and the diameter of part of the conductor in the lower substrate.

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