A method and system for monitoring solder melting state

Abstract

The present invention relates to the field of chip welding technology, and in particular to a method and system for monitoring the molten state of solder. The solder molten state monitoring method uses a solder sample with an offset metal backplate as a measurement object, emits electromagnetic waves and receives its reflected signals, and analyzes the power peak of the reflected signals to calculate the dielectric constant of the solder. Since the transformation of solder from solid to liquid is a phase change process, its dielectric constant will undergo a sudden change during this process. Therefore, the molten state of the solder can be monitored by measuring the dielectric constant of the solder. The present application can monitor the changes in the dielectric constant of the solder in real time and quickly capture the turning point of the solder melting process. This real-time monitoring and analysis capability provides strong support for the precise control of welding temperature and time.

Description

Technical Field

[0001] The present invention relates to the technical field of chip welding, and in particular to a method and system for monitoring the melting state of solder. Background Art

[0002] Chip soldering refers to the process of connecting a chip to a circuit board or other device. Before soldering, the compatibility between the chip and the soldering area must be considered. During soldering, parameters such as temperature, time, and pressure must be strictly controlled. The solder's molten state must also be monitored to ensure that the solder joints meet quality standards and avoid solder failure or chip damage during the soldering process. Monitoring the solder's molten state is not only fundamental to ensuring the effective execution of microelectronics manufacturing processes but also a key technical guarantee for achieving high-reliability and high-performance electronic products.

[0003] Currently, commonly used methods for monitoring the molten state of chip solder joints include real-time thermal imaging or online image detection to monitor the solder molten state, helping operators adjust soldering parameters in a timely manner. However, for chip soldering, the resolution of thermal imaging technology is limited and cannot provide sufficient detail resolution. As a result, subtle temperature changes and melting conditions cannot be accurately captured when monitoring the solder molten state. Online image detection technology is also sensitive to environmental conditions such as light, and the acquired image data requires complex processing and analysis, making it less adaptable. Summary of the Invention

[0004] The present invention provides a method and system for monitoring the molten state of solder based on dielectric constant, which performs real-time monitoring of the molten state of solder by monitoring changes in dielectric constant, thereby improving the accuracy and reliability of welding.

[0005] In order to achieve the above objectives, this application is implemented through the following technical solutions:

[0006] In a first aspect, the present application provides a method for monitoring the melting state of solder, comprising: obtaining the offset distance d between the solder and the metal backplane when the vector network analyzer is in time domain mode; ofs , where the solder is located above the metal backing plate and there is no direct contact between the solder and the metal backing plate; the surface of the solder away from the metal backing plate is set as the first interface, and the surface of the solder close to the metal backing plate is set as the second interface, and the distance d between the first interface and the second interface is obtained; the air gap d between the antenna of the vector network analyzer and the solder is obtained. s ; Use the signal receiving end of the vector network analyzer to obtain the reflected signal generated by the electromagnetic wave emitted by the antenna and irradiated on the solder and the metal backplane; combined with the offset distance d ofs , distance d, air gap d sThe dielectric constant of the solder is calculated based on the dielectric constant of the solder. The comprehensive evaluation value is compared with the experimental value under the known molten state to determine whether the solder has reached a fully molten state.

[0007] In a second aspect, the present application provides a solder melting state monitoring system, comprising a memory, a processor, and a computer program stored in the memory and capable of running on the processor. When the processor executes the computer program, the steps of the solder melting state monitoring method provided by the present invention are implemented.

[0008] Beneficial effects:

[0009] The solder molten state monitoring method and system provided by the present invention uses a solder sample with an offset metal backing as the measurement object. By emitting electromagnetic waves and receiving the reflected signal, the system analyzes the peak power of the reflected signal to calculate the solder's dielectric constant. Since the transition from solid to liquid solder is a phase change, during which its dielectric constant undergoes a sudden change, the solder's molten state can be monitored by measuring its dielectric constant. The present invention can monitor changes in the solder's dielectric constant in real time, quickly identifying turning points in the solder melting process. This real-time monitoring and analysis capability provides strong support for precise control of soldering temperature and time. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a flow chart of a method for monitoring the melting state of solder according to the present invention;

[0011] Figure 2 FIG1 is a time response diagram of a reflected signal of a solder sample with an offset metal backing according to an embodiment of the present invention;

[0012] Figure 3 Graph showing the dielectric constant variation of the solder in different molten states according to an embodiment of the present invention.

[0013] Reference numerals: U1 - antenna of vector network analyzer, U2 - metal back plate. DETAILED DESCRIPTION

[0014] The following is a clear and complete description of the technical solutions of the present invention. It should be understood that the embodiments described are only a portion of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention.

[0015] Unless otherwise defined, the technical or scientific terms used in the present invention shall have the usual meanings understood by persons of ordinary skill in the field to which the present invention belongs. The words "first", "second" and similar terms used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, words such as "one" or "a" do not indicate a quantity limitation, but rather indicate the existence of at least one. Words such as "connected" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship also changes accordingly.

[0016] like Figure 1 As shown, the present application provides a method for monitoring the melting state of solder, comprising:

[0017] S1: When the vector network analyzer is in time domain mode, obtain the offset distance d between the solder and the metal backplane ofs ,like Figure 2 As shown, wherein the solder is located above the metal back plate, and there is no direct contact between the solder and the metal back plate;

[0018] In one example, a substrate is placed between the solder and the metal backing. While the substrate does affect the calculation of the solder's dielectric constant, since the substrate's dielectric properties remain stable throughout the solder melting process, it can be pre-corrected in the algorithm, ensuring that the final solder dielectric constant value is unaffected by the substrate. Therefore, the substrate's influence will not be considered in subsequent descriptions of solder dielectric constant measurements.

[0019] S2: setting the surface of the solder away from the metal back plate as a first interface, and the surface of the solder close to the metal back plate as a second interface, and obtaining a distance d between the first interface and the second interface;

[0020] S3: Obtain the air gap d between the antenna of the vector network analyzer and the solder s ;

[0021] S4: using a signal receiving end of the vector network analyzer, obtaining a reflected signal generated by the electromagnetic wave emitted by the antenna and irradiated on the solder and the metal backplane;

[0022] S5: Combine the offset distance d ofs , the distance d, the air gap d s and the reflected signal, calculating the dielectric constant of the solder; the specific steps include:

[0023] S501: Combine the offset distance d ofs , the distance d and the air gap d s , performing Fourier transform and inverse Fourier transform on the reflected signal;

[0024] First, the reflected signal is subjected to Fourier transform; wherein the reflected signal satisfies the following constraints in the time domain:

[0025] s n (t) = P n (t)*G n (t)*T n (t)*A n (t-τ n )*s out (t) (1);

[0026] Where n is the serial number of the reflected signal; s n (t) represents the reflection signal, s1(t) represents the reflection signal generated by the electromagnetic wave at the first interface of the solder, s2(t) represents the reflection signal generated by the electromagnetic wave at the second interface of the solder, and s3(t) represents the reflection signal generated by the electromagnetic wave on the metal backing; * represents the convolution operation; P n (t) represents the free space path loss term; G n (t) represents the reflection term of the I-II interface, II-III interface, and III-IV interface; T n (t) represents the transmission term between the I-II interface, the II-III interface, and the III-IV interface; the I-II interface represents the interface between region I and region II, and so on, the II-III interface represents the interface between region II and region III, and the III-IV interface represents the interface between region III and region IV; region I represents the air region between the antenna and the solder, region II represents the internal region of the solder, region III represents the offset region between the solder and the metal backplane, and region IV represents the internal region of the metal backplane; A n (t-τ n ) represents the effective attenuation and phase delay inside the solder; τ n is the arrival time of the reflected signal; S out (t) is the electromagnetic wave signal emitted by the antenna;

[0027] When Fourier transforming formula (1) from the time domain to the frequency domain, the following constraints are met:

[0028]

[0029] G1(ω)=g 12 (ω), G2(ω)=g 23 (ω), G3(ω)=-1 (3);

[0030] T1(ω)=1,T2(ω)=t 12 (ω)t 21 (ω), T3(ω)=t 12 (ω)t 23 (ω) t32 (ω)t 21 (ω)(4);

[0031]

[0032]

[0033]

[0034] Among them, P n (w) and P(w) both represent free space path loss terms; g 12 (ω) represents the reflection coefficient on the I-II interface, g 21 (ω) represents the reflection coefficient on the II-I interface, g 23 (ω) represents the reflection coefficient on the II-III interface, g 32 (ω) represents the reflection coefficient on the III-II interface; t 12 (w) represents the transmission coefficient at the I-II interface, t 21 (w) represents the transmission coefficient at the II-I interface, t 23 (w) represents the transmission coefficient at the II-III interface, t 32 (w) represents the projection coefficient at the III-II interface; n(w) is the refractive index of the solder; k0 is the free space wave number; j is the imaginary unit; ε0 is the dielectric constant in vacuum; ε r is the dielectric constant of the solder; σ e is the electrical conductivity of the solder;

[0035] Then, the Fourier transformed reflected signal is subjected to inverse Fourier transform; after conversion from frequency domain to time domain, due to g 12 (t), A2(t) and A3(t) are simplified to:

[0036]

[0037]

[0038]

[0039] Where δ(t) is the Dirac function; γ is an intermediate calculation parameter used to simplify the calculation; and η0 represents the intrinsic impedance in air.

[0040] In one example, when the electromagnetic wave is incident from region 1 to the first interface of the solder, part of the electromagnetic wave will be reflected back to form the first reflected wave g 12 (ω), the rest of the electromagnetic waves that pass through the first interface will reach the metal backplane interface. Since the metal backplane is reflective, these electromagnetic waves will be reflected back into the solder. The electromagnetic waves reflected back by the metal backplane pass through the solder again and are partially reflected and partially transmitted when they reach the first interface. In this way, the electromagnetic waves are reflected and transmitted back and forth inside the solder and between the solder and the metal backplane, forming multiple reflections. The cumulative effect of all these reflection processes is expressed as the total reflection coefficient g mul (ω) is used to describe it, and its expansion is:

[0041]

[0042]

[0043] g 34 (ω)=G3(ω)=-1 (13);

[0044] Wherein, formula (13) indicates that the metal backplane is fully reflective.

[0045] It is worth emphasizing that formulas (11)-(13) are only used to describe the cumulative effect of electromagnetic waves in the process of multiple reflections.

[0046] S502: Calculating the reflected power peak of the reflected signal and the dielectric constant of the solder;

[0047] First, the reflected power peak value of the reflected signal is calculated; the reflected power of s1(t), s2(t) and s3(t) is simplified to:

[0048] E1(t)≈γ 2 P(t)*s out (t-τ1)(14);

[0049]

[0050]

[0051] When considering the peak value of reflected power, P(t)*s out (t-τ1), P(t)*s out (t-τ2) and P(t)*s out (t-τ3)These three terms are equal;

[0052] Then, calculate the dielectric constant ε of the solder r :

[0053]

[0054] Among them, H is an intermediate calculation parameter used to simplify the calculation; and Denote the peak values ​​of the reflected powers E2(t) and E3(t) of s2(t) and s3(t), respectively.

[0055] S6: Obtain a comprehensive evaluation value based on the dielectric constant of the solder, and compare the comprehensive evaluation value with the experimental value under a known molten state to determine whether the solder has reached a fully molten state. The details are as follows:

[0056] S601: Processing the dielectric constant of the solder. The data processing method includes one of the following two methods:

[0057] S601A: When the dielectric constant of the solder is obtained through a point of the solder, the dielectric constant value χ of the solder is equal to the dielectric constant ε of the solder. r equal:

[0058] χ=ε r (18);

[0059] S601B: Obtain the dielectric constant of the solder at N different points When N≥2, the dielectric constant of each point is weighted averaged to obtain the solder dielectric constant value χ; the solder dielectric constant value χ satisfies the following relationship:

[0060]

[0061] Among them, w i is the weight of the i-th point;

[0062] S602: Obtain a comprehensive evaluation value W for judging the melting state of the solder based on the solder dielectric constant value and the real-time temperature. The comprehensive evaluation value satisfies the following relationship:

[0063] W = αχ + βT (20);

[0064] Where, χ is the dielectric constant of the solder; T is the real-time temperature of the solder; α and β are empirical values;

[0065] S603: Compare the comprehensive evaluation value with the melting state range of the solder, such as Figure 3 As shown in the figure, if the comprehensive evaluation value is within the range of the full melting stage, it means that the solder has been completely melted.

[0066] This application also provides a solder molten state monitoring system, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the above-described method. This solder molten state monitoring system can implement each of the above-described embodiments of solder molten state monitoring and achieve the same beneficial effects, and is not further described here.

[0067] The above describes in detail the preferred embodiments of the present invention. It should be understood that those skilled in the art can make numerous modifications and variations based on the concepts of the present invention without inventive effort. Therefore, any technical solutions that can be derived by those skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art should be within the scope of protection defined by the claims.

Claims

1. A method for monitoring the melting state of solder, characterized in that: include: S1: When the vector network analyzer is in time domain mode, obtain the offset distance d between the solder and the metal backplane ofs , wherein the solder is located above the metal back plate, and there is no direct contact between the solder and the metal back plate; S2: setting the surface of the solder away from the metal back plate as a first interface, and the surface of the solder close to the metal back plate as a second interface, and obtaining a distance d between the first interface and the second interface; S3: Obtain the air gap d between the antenna of the vector network analyzer and the solder s ; S4: using a signal receiving end of the vector network analyzer, obtaining a reflected signal generated by the electromagnetic wave emitted by the antenna and irradiated on the solder and the metal backplane; S5: Combine the offset distance d ofs , the distance d, the air gap d s and the reflected signal, calculating the dielectric constant of the solder; S6: Obtaining a comprehensive evaluation value according to the dielectric constant of the solder, and comparing the comprehensive evaluation value with an experimental value under a known molten state to determine whether the solder has reached a fully molten state.

2. A method for monitoring the melting state of solder according to claim 1, characterized in that: The S5 includes: S501: Combine the offset distance d ofs , the distance d and the air gap d s , performing Fourier transform and inverse Fourier transform on the reflected signal; S502: Calculate the reflected power peak value of the reflected signal and the dielectric constant of the solder.

3. A method for monitoring the melting state of solder according to claim 2, characterized in that: The S501 includes: First, the reflected signal is subjected to Fourier transform; wherein the reflected signal satisfies the following constraints in the time domain: s n (t)=P n (t)*G n (t)*T n (t)*A n (t-τ n )*s out (t) (1); Where n is the serial number of the reflected signal; s n (t) represents the reflection signal, s1(t) represents the reflection signal generated by the electromagnetic wave at the first interface of the solder, s2(t) represents the reflection signal generated by the electromagnetic wave at the second interface of the solder, and s3(t) represents the reflection signal generated by the electromagnetic wave on the metal backing; * represents the convolution operation; P n (t) represents the free space path loss term; G n (t) represents the reflection term of the I-II interface, II-III interface, and III-IV interface; T n (t) represents the transmission term between the I-II interface, the II-III interface, and the III-IV interface; the I-II interface represents the interface between region I and region II, the II-III interface represents the interface between region II and region III, and the III-IV interface represents the interface between region III and region IV; region I represents the air region between the antenna and the solder, region II represents the internal region of the solder, region III represents the offset region between the solder and the metal backplane, and region IV represents the internal region of the metal backplane; A n (t-τ n ) represents the effective attenuation and phase delay inside the solder; τ n is the arrival time of the reflected signal; S out (t) is the electromagnetic wave signal emitted by the antenna; When Fourier transforming formula (1) from the time domain to the frequency domain, the following constraints are met: G1(ω)=g 12 (ω), G2(ω)=g 23 (ω), G3(ω)=-1 (3); T1(ω)=1,T2(ω)=t 12 (ω)t 21 (ω), T3(ω)=t 12 (ω)t 23 (ω)t 32 (ω)t 21 (oh) (4); Among them, P n (w) and P(w) both represent free space path loss terms; g 12 (ω) represents the reflection coefficient on the I-II interface, g 21 (ω) represents the reflection coefficient on the II-I interface, g 23 (ω) represents the reflection coefficient on the II-III interface, g 32 (ω) represents the reflection coefficient on the III-II interface; t 12 (w) represents the transmission coefficient at the I-II interface, t 21 (w) represents the transmission coefficient at the II-I interface, t 23 (w) represents the transmission coefficient at the II-III interface, t 32 (w) represents the projection coefficient at the III-II interface; n(w) is the refractive index of the solder; k0 is the free space wave number; j is the imaginary unit; ε0 is the dielectric constant in vacuum; ε r is the dielectric constant of the solder; σ e is the electrical conductivity of the solder; Then, the Fourier transformed reflected signal is subjected to inverse Fourier transform; after conversion from frequency domain to time domain, due to g 12 (t), A2(t) and A3(t) are simplified to: Where δ(t) is the Dirac function; γ is an intermediate calculation parameter used to simplify the calculation; and η0 represents the intrinsic impedance in air.

4. A method for monitoring the melting state of solder according to claim 3, characterized in that: The S502 includes: First, the reflected power peak value of the reflected signal is calculated; the reflected power of s1(t), s2(t) and s3(t) is simplified to: E1(t)≈γ 2 P(t)*s out (t-τ1)(11); When considering the peak value of reflected power, P(t)*s out (t-τ1), P(t)*s out (t-τ2) and P(t)*s out (t-τ3)These three terms are equal; Then, calculate the dielectric constant ε of the solder r : Among them, H is an intermediate calculation parameter used to simplify the calculation; and Denote the peak values ​​of the reflected powers E2(t) and E3(t) of s2(t) and s3(t), respectively.

5. The method for monitoring the melting state of solder according to claim 1, wherein: The S6 includes: S601: Processing the dielectric constant of the solder. The data processing method includes one of the following two methods: S601A: When the dielectric constant of the solder is obtained through a point of the solder, the dielectric constant value χ of the solder is equal to the dielectric constant ε of the solder. r equal: x=e r (15); S601B: Obtain the dielectric constant set of solder at N different points of solder When N≥2, the dielectric constant of each point is weighted averaged to obtain the solder dielectric constant value χ; the solder dielectric constant value χ satisfies the following relationship: Among them, w i is the weight of the i-th point; S602: Obtain a comprehensive evaluation value W for judging the melting state of the solder based on the solder dielectric constant value and the real-time temperature. The comprehensive evaluation value satisfies the following relationship: W = αχ + βT (17); Where, χ is the dielectric constant of the solder; T is the real-time temperature of the solder; α and β are empirical values; S603: comparing the comprehensive evaluation value with the melting state range of the solder; if the comprehensive evaluation value is within the full melting stage range, it indicates that the solder has been completely melted.

6. A solder melting state monitoring system comprising a memory, a processor, and a computer program stored in the memory and capable of running on the processor, characterized in that: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 5 are implemented.

7. A solder melting state monitoring device, comprising a memory, a processor, and a computer program stored in the memory and capable of running on the processor, characterized in that: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 5 are implemented.

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