CN100377622C - Process for making backing electrode electret condenser type microphones - Google Patents
Process for making backing electrode electret condenser type microphones Download PDFInfo
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- CN100377622C CN100377622C CNB2004100153395A CN200410015339A CN100377622C CN 100377622 C CN100377622 C CN 100377622C CN B2004100153395 A CNB2004100153395 A CN B2004100153395A CN 200410015339 A CN200410015339 A CN 200410015339A CN 100377622 C CN100377622 C CN 100377622C
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Abstract
The present invention relates to a method for manufacturing back pole electret condenser type microphones, particularly to a method for manufacturing back pole electret condenser type microphones with the advantages of high sensitivity and favorable stability. In the present invention, a thin polyester film is tensioned on a tool to form a fixed vibrating film, and an adjusting ring on the tool is adjusted to ensure that the resonance frequency in a testing sound field of the thin film is within a design range to control the tension force position of the thin film. After a nickel film with a certain thickness is plated in a vacuum environment through vaporization, the intensity of the tension force of the thin film is adjusted again, and then, a group of supporting rings are stuck to the thin film. A single vibrating film assembly is manufactured through the process steps of flattening, drying, division, etc. The present invention can guarantee the equality of the tension force of vibrating films of microphone vibrating film assemblies manufactured in the same batch by using one thin film as well as the repeatability of the tension force of vibrating films of microphone vibrating film assemblies of different batches in the process of mass production, so that the consistency of the product quality is effectively controlled in the mass production of microphones.
Description
The technical field is as follows:
the invention relates to a method for manufacturing a back electrode electret condenser microphone.
The background art comprises the following steps:
the pressure type condenser microphone adopting the back electrode electret mode selects the polyester film as the vibrating diaphragm, and the strength of the polyester film is usually 1 to 2 orders of magnitude smaller than that of a metal film, so that the equivalent force of the vibrating diaphragm is smooth (the force determines f of the vibrating diaphragm) 01 ) Mainly composed of a rear cavity V 2 A contribution. According to theoretical derivation about common pressure type capacitance microphones, it is not difficult to obtain the open-circuit sensitivity of the pressure type electret microphone in the main working frequency band as follows:
in the formula C A2 Is the equivalent acoustic compliance of the posterior chamber;
s is the effective area of the plate;
ε 1 、ε 2 the dielectric constants of air and electret film material, respectively;
P 0 gamma is the ratio of atmospheric pressure, constant volume heat capacity of air and constant pressure heat capacity;
therefore, the above formula can also be expressed as;
C A2 large, then E 0 Large, and f 01 Small (narrow operating band);
C A2 small, then E 0 Small, and f 01 High (operating frequency bandwidth).
The circular diaphragm fixed on the circumference generates forced vibration under the action of sound pressure, the resonance frequency of the diaphragm is equal to the normal frequency, and the fundamental frequency
In the above formula, r is the radius of the diaphragm, T is the tension, and λ is the areal density of the diaphragm.
Therefore, it can be seen that the electro-acoustic performance indexes such as sensitivity, frequency response range and curve flatness of the back electrode electret capacitor microphone are mainly determined by the following factors: the surface charge density of the electret, the tension of the diaphragm, the distance of the diaphragm from the backplate, and another factor that fails to appear in the above formula, are the impedance transformer properties of the output microphone electrical signal. In order to effectively control the electroacoustic characteristic parameters of the product to meet the design requirements and ensure consistency in mass production, it is important to control the above factors in the manufacturing process of the product.
Among these factors, the distance between the diaphragm and the back plate is determined by the thickness of the spacer, and the performance of the impedance transformer is determined by the parameters of the FET tube and the capacitor, so the stability of the electroacoustic performance of the electret condenser microphone and the consistency in mass production are mainly determined by the tension of the diaphragm on the support ring and the consistency of the surface charge density formed when the electret thin-film material is charged during the manufacturing process. Meanwhile, in order to enable the electro-acoustic performance indexes such as sensitivity, frequency response curve and the like of the electret condenser microphone to meet design requirements, an optimal matching scheme exists between the tension of the vibrating diaphragm and the surface charge density of the electret.
In the existing technology for manufacturing electret condenser microphones, the electret surface charge density is measured by a surface potentiometer, and the tension of a vibrating diaphragm is mainly controlled by the experience of an operator in the manufacturing process due to the lack of a proper and effective measuring means. This makes it difficult to ensure a consistent degree of tension when the diaphragm is attached to the support ring. If the vibrating diaphragm is tightened too tightly, the too large tension not only can not improve the sensitivity of the microphone, but also can cause the vibrating diaphragm to generate irreversible deformation, thereby influencing the consistency and stability of the performance index of the microphone. In addition, when the diaphragm tension is too large, the surface charge density of the electret film must be increased in order to achieve a predetermined value of the microphone sensitivity, and the stability of the residual charge of the electret material is deteriorated in the case of an excessively high charge density, which also affects the stability of the microphone sensitivity. Conversely, if vibrating diaphragm tension is too little, the diaphragm corrugates easily, and the cladding material quality when coating by vaporization nickel membrane worsens, and assembles into the microphone after, the diaphragm can be because of electrostatic attraction attaches on the back plate, influences product property ability.
The invention aims to provide a method for manufacturing a back-electrode electret condenser microphone with high sensitivity and good stability, which effectively controls the tension of a vibrating diaphragm through a special tool and combines the measurement and adjustment of the surface charge density of an electret film to ensure that the manufactured electret condenser microphone has the acoustic performance indexes such as sensitivity, frequency response range, curve flatness and the like which meet the design requirements, and the indexes have good consistency when products are produced in batches.
The invention content is as follows:
the invention provides a method for manufacturing a back electrode electret capacitor microphone with high sensitivity and good stability, wherein a polyester film is tightened on a tool to form a fixed vibrating diaphragm, and the resonance frequency of the film in a test sound field is within a design range by adjusting an adjusting ring on the tool so as to control the tension of the film; after a nickel film with a certain thickness is evaporated in a vacuum environment, the tension of the film is adjusted again, and then a group of support rings are bonded on the film; and then the manufacturing of a single vibrating diaphragm component is finished through the procedures of flattening, drying, dividing and the like.
The invention tightens the polyester film on the tool to form a circular vibrating membrane with fixed circumference. On a large membrane stretched by the tool, three areas of an outer ring, a middle ring and an inner ring are divided, 20 vibrating diaphragms are taken from each area to be manufactured into a microphone, the sensitivity value of the microphone is tested, and the sensitivity value is averaged. The frock include five parts: the film stretching device comprises a film stretching base, a film stretching ring, a frequency modulation ring, an adjusting ring and an O-shaped rubber ring, wherein the O-shaped rubber ring is embedded into a clamping groove of an inner ring of the film stretching ring, and the film stretching ring uniformly stretches a polyester film on the film stretching base through the O-shaped rubber ring. The frequency modulation ring and the adjusting ring are sleeved in the film stretching base, the adjusting ring is in threaded connection with the base, the frequency modulation ring is arranged on the upper portion of the adjusting ring and is in uniform contact with the tensioned film, and the tensioning degree of the film can be adjusted by adjusting the height of the adjusting ring in the base. The frequency modulation ring is freely arranged on the upper part of the adjusting ring, the frequency modulation ring and the adjusting ring are in smooth contact, and the height of the adjusting ring in the base can be adjusted through self rotation.
The vibrating diaphragm is adhered to the support ring with equal tension, and the back plate electret is provided with resident charges with the same density. And controlling the deformation of the polyester film tensioned on the tool within the elastic limit during tensioning, and effectively controlling the tension of the vibrating diaphragm through the tool. The resonance frequency is 310Hz-360Hz and the corresponding diaphragm tension of the area nearby. And controlling the tension of the diaphragm and the surface charge density value after electret charging to manufacture the back electrode electret microphone with a frequency response curve.
The invention effectively controls the tension of the vibrating diaphragm through the special tool, and combines the measurement and adjustment of the surface charge density of the electret film, so that the manufactured electret capacitor microphone has the sensitivity, the frequency response range, the curve flatness and other acoustic performance indexes which meet the design requirements, and the indexes have good consistency during the mass production of products. By adopting the special tool, the deformation of the polyester film tensioned on the tool can be controlled within the elastic limit, so that the uniform distribution of the tension in the whole film is ensured. By measuring the resonant frequency of the tensioned film in a test sound field, an effective way is provided for measuring the tension in the film. The method not only ensures that the vibrating diaphragms in the same batch of microphone vibrating diaphragm assemblies manufactured by adopting one film have the same tension, but also can ensure the repeatability of the tension of the vibrating diaphragms in different batches of microphone vibrating diaphragm assemblies in the batch production process, thereby effectively controlling the consistency of the product quality in the batch production of the microphones.
Drawings
FIG. 1 illustrates a diaphragm assembly in a back-pole electret microphone;
FIG. 2 is a cross-sectional view of the special tool of the present invention;
FIG. 3 is a schematic perspective view of the components of the special tooling;
FIG. 4 is a diagram showing the test results of the consistency of the sensitivity of microphones manufactured by the special tool of the present invention;
FIG. 5 is a graph showing the results of a test on the relationship between the sensitivity of a microphone manufactured by the method of the present invention and the tension of a thin film;
FIG. 6 is a graph showing the results of a test on the relationship between the sensitivity of a microphone manufactured by the method of the present invention and the density of electric charges in an electret;
fig. 7 shows a typical frequency response curve for a microphone manufactured by the method of the invention.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings.
A back-pole electret condenser microphone comprises several core components: a vibrating diaphragm component (see attached figure 1), a back plate covered with electret film material, a gasket and a PCB board pasted with an impedance conversion circuit. The above components are packaged in a casing with sound transmission holes together with a back plate supporting device and a connecting device.
The sensitivity, frequency response range, curve flatness and other acoustic performance indexes of the back electrode electret capacitor microphone are mainly determined by the following factors: the surface charge density of the electret, the tension of the diaphragm, the distance between the diaphragm and the back plate and the performance of an impedance converter for outputting an electric signal of the microphone. In order to effectively control the electroacoustic characteristic parameters of the product to meet the design requirements and ensure the consistency in batch production, it is very important to control the factors in the manufacturing process of the product.
Among these factors, the distance between the diaphragm and the back plate is determined by the thickness of the spacer between the diaphragm and the back plate, and the performance of the impedance converter is determined by the parameters of the FET tube and the capacitor, so that the stability of the electroacoustic performance of the electret condenser microphone and the consistency in mass production are mainly determined by the tension of the diaphragm assembled on the support ring and the consistency of the surface charge density formed when the electret film material is charged in the manufacturing process. Meanwhile, in order to enable the electro-acoustic performance indexes such as sensitivity, frequency response curve and the like of the electret capacitor microphone to meet design requirements, the attached drawing provided by the invention illustrates that an optimal matching scheme exists between the tension of the vibrating diaphragm and the surface charge density of the electret.
The diaphragm assembly is composed of a diaphragm and a support ring thereof, as shown in figure 1, the radius of the diaphragm 6 is the same as the outer diameter of the support ring 7, for example, a microphone with an outer diameter of 6mm, and the support ring 7 is a stainless steel ring with an outer diameter of about 5.4mm, an inner diameter of 3.6mm and a thickness of about 0.3 mm. The diaphragm 6 is a polyester film having a thickness of about 4.8 μm, such as PET, having high temperature resistance and a high young's modulus. The vibration membrane component is manufactured by the following method, more than 100 vibration membrane components are manufactured each time: the method comprises the steps of tightening a polyester film on a special tool (shown in attached figures 2 and 3) to form a circular vibrating diaphragm with a fixed circumference, enabling the resonance frequency of the film in a test sound field to be within a design range by adjusting an adjusting ring 2 on the special tool to control the tension of the film to be at a preset value, after a nickel film with a certain thickness is evaporated in a vacuum environment, adjusting the tension of the film to the preset value again by adopting the same method, and then bonding a group of support rings on the film. The manufacturing of a single vibrating membrane component is completed through the procedures of flattening, drying, dividing and the like, so that the vibrating membranes in all the manufactured vibrating membrane components are adhered to the support ring with equal tension. The back plate electret is retained with the same density of the resident charges according to the design requirement, the manufactured microphone has ideal sensitivity and frequency response curve, and all the electroacoustic performance indexes of the product have good consistency during batch production.
The special tool comprises five parts: the film stretching device comprises a film stretching base 5, a film stretching ring 4, a frequency modulation ring 1, an adjusting ring 2 and an O-shaped rubber ring 3. The O-shaped rubber ring 3 is embedded into a clamping groove of an inner ring of the film stretching ring 4, and the film stretching ring 4 uniformly tensions a polyester film on the film stretching base 5 through the O-shaped rubber ring 3. The frequency modulation ring 1 and the adjusting ring 2 are sleeved in the film stretching base 5, the adjusting ring 2 is in threaded connection with the base 5, the frequency modulation ring 1 is arranged on the upper portion of the adjusting ring 2 and is in uniform contact with a tensioned film, and the purpose of adjusting the tensioning degree of the film can be achieved by adjusting the height of the adjusting ring 2 in the base 5.
By adopting the special tool, the deformation of the polyester film tensioned on the tool can be controlled within the elastic limit, so that the uniform distribution of the tension in the whole film is ensured. By measuring the resonant frequency of the tensioned film in a test sound field, an effective way is provided for measuring the tension in the film. The tension of the vibrating diaphragms in the same batch of microphone vibrating diaphragm assemblies manufactured by one film is the same, repeatability of the tension of the vibrating diaphragms in different batches of microphone vibrating diaphragm assemblies in the batch production process can be guaranteed, and consistency of product quality in batch production of microphones is effectively controlled.
The magnitude of the tension in the film is measured according to the resonance frequency of the film in a test sound field, the magnitude of the charge density in the electret is measured according to the magnitude of the charged electret surface potential, the sensitivity values of electret microphones manufactured under different conditions are respectively tested, the number of samples in each condition is 20, and the average values of the samples are calculated and tabulated to be plotted, and the tabulated values are shown in attached figures 4, 5 and 6. The calculation shows that: the standard deviation of the 20 sets of sensitivity data in each case was less than 2dB, and the data was consistent well.
The relevant test results also show that: when the charging voltage used is too high and the surface potential of the charge residing in the electret film exceeds 120V, the time stability of the residing charge becomes poor. That is, the higher the charging voltage is, the faster the surface potential decreases, when the surface potential value of the electret film is measured every 4 hours after charging. Therefore, although increasing the charging voltage at the time of electret charge can significantly improve the microphone sensitivity, we have used charging voltage values limited to the surface potential of less than 120V in subsequent experiments and actual production.
The data sources of FIG. 4 are: on a large membrane stretched by a special tool, dividing three areas of an outer ring, a middle ring and an inner ring, taking 20 vibrating membranes in each area to manufacture a sound transmitter to test the sensitivity value of the sound transmitter, and taking the average value of the sound transmitter, wherein the result shows that: the diaphragm is made from different areas on the same large diaphragm, the microphone sensitivity consistency is good, and the uniformity of the tension distribution in the same large diaphragm stretched by a special tool is further proved. It is worth mentioning that: the resonance frequency of the large membrane and the resonance frequency of the local diaphragm are different due to different radiuses, but have a one-to-one corresponding relation.
Fig. 5 then shows: the microphone sensitivity increases with increasing charge density in the electret under different diaphragm tensions. Both fig. 5 and fig. 4 show: the sensitivity of the microphone has an optimal value under the condition that the resonance frequency is 310Hz-360Hz and the vibration diaphragm tension corresponding to the area nearby the resonance frequency. Fig. 5 also shows that when the surface potential of the back electrode electret after charging is 80V-90V, the microphone sensitivity difference caused by the diaphragm tension difference is less.
Fig. 6 shows the behavior of the sensitivity of an electret microphone as a function of the diaphragm tension at different electret charge densities. As is evident from the figure: the sensitivity of the microphone has an optimal value under the condition that the resonance frequency is 310Hz-360Hz and the vibration diaphragm tension corresponding to the area nearby the resonance frequency.
Fig. 7 shows that the back electrode electret microphone manufactured by controlling the diaphragm tension and the surface charge density value after electret charging by using the method of the present invention has high sensitivity, good consistency and an ideal frequency response curve, wherein the frequency response curve of a typical microphone is given, and the curve has wide bandwidth and good flatness.
Claims (7)
1. A method for manufacturing a back electrode electret condenser microphone is characterized in that a polyester film is tightened on a tool to form a fixed vibrating diaphragm, the resonance frequency of the film in a test sound field is enabled to be in a design range by adjusting an adjusting ring on the tool so as to control the tension of the film, and the tool comprises five parts: the stretch film device comprises a stretch film base, a stretch film ring, a frequency modulation ring, an adjusting ring and an O-shaped rubber ring, wherein the O-shaped rubber ring is embedded into a clamping groove of an inner ring of the stretch film ring; after a layer of nickel film is evaporated in a vacuum environment, the tension of the film is adjusted again, and then a group of support rings are bonded on the film; and finishing the manufacture of a single vibration membrane component through the procedures of flattening, drying and dividing.
2. A method of making a back-electrode electret condenser microphone as claimed in claim 1, wherein the polyester film is stretched over the tool to form a circumferentially fixed circular diaphragm.
3. The method of claim 2, wherein the tool is used to stretch a diaphragm into three areas, namely an outer circle, a middle circle and an inner circle, 20 diaphragms are taken from each area to form a microphone, and the sensitivity of the microphone is measured and averaged.
4. A method of making an electret condenser microphone with a back electrode as claimed in claim 1, wherein the frequency-adjusting ring freely rests on the top of the adjusting ring with a smooth contact therebetween, and the height of the adjusting ring in the base can be adjusted by rotating itself.
5. A method for making an electret condenser microphone in accordance with claim 1, wherein the diaphragm is adhered to the support ring with equal tension to hold the back plate electret with the same density of resident charges.
6. The method for manufacturing a back electrode electret condenser microphone as claimed in claim 1, wherein the deformation of the mylar film tensioned on the tooling is controlled within the elastic limit, and the magnitude of the diaphragm tension is effectively controlled by said tooling.
7. The method of manufacturing a back electrode electret condenser microphone of claim 6, wherein the resonance frequency is a diaphragm tension corresponding to a region of 310HZ-360 HZ.
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| CNB2004100153395A CN100377622C (en) | 2004-02-11 | 2004-02-11 | Process for making backing electrode electret condenser type microphones |
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| CNB2004100153395A CN100377622C (en) | 2004-02-11 | 2004-02-11 | Process for making backing electrode electret condenser type microphones |
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| CN1655650A CN1655650A (en) | 2005-08-17 |
| CN100377622C true CN100377622C (en) | 2008-03-26 |
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| CN1812639B (en) * | 2005-12-05 | 2011-11-23 | 程光 | Pre-stress vibrating diaphragm |
| CN101102622B (en) * | 2006-07-07 | 2011-12-14 | 欧力天工股份有限公司 | Making method for vibration film assembly and capacitance microphone |
| CN101207944B (en) * | 2006-12-18 | 2011-05-11 | 深圳市豪恩声学股份有限公司 | Method for manufacturing microphone diaphragm |
| WO2017212697A1 (en) * | 2016-06-09 | 2017-12-14 | アルプス電気株式会社 | Method for producing sound-generating device |
| CN106108119A (en) * | 2016-08-12 | 2016-11-16 | 云南中烟工业有限责任公司 | A kind of with vibration shape oil dripping nebulizer |
| CN106037019A (en) * | 2016-08-12 | 2016-10-26 | 云南中烟工业有限责任公司 | Vibration starting-vibration following atomizer |
| CN107734421A (en) * | 2017-11-06 | 2018-02-23 | 深圳市威索尼可电子有限公司 | A kind of panel earphone pronunciation device, earphone and assembly method |
| CN109391881B (en) * | 2017-11-30 | 2024-01-19 | 深圳市吉瑞德隆电子科技有限公司 | Plane vibrating diaphragm loudspeaker |
| CN108430007A (en) * | 2018-05-16 | 2018-08-21 | 周代军 | A kind of capacitor microphone vibrating diaphragm and microphone and production method |
| CN109743670B (en) * | 2018-12-27 | 2021-03-23 | 深圳市新厚泰塑胶电子有限公司 | Design method for controlling initial phase of ECM |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1429049A (en) * | 2001-12-28 | 2003-07-09 | 星精密株式会社 | Electret condenser microphone and mfg. method |
| CN1455618A (en) * | 2003-05-23 | 2003-11-12 | 百富非凡机电设备（北京）有限公司 | Loudspeaker vibrating diaphragm base material structure and manufacturing method thereof |
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Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1429049A (en) * | 2001-12-28 | 2003-07-09 | 星精密株式会社 | Electret condenser microphone and mfg. method |
| CN1455618A (en) * | 2003-05-23 | 2003-11-12 | 百富非凡机电设备（北京）有限公司 | Loudspeaker vibrating diaphragm base material structure and manufacturing method thereof |
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