Chip component and MEMS microphone

Abstract

Chip component for use in a MEMS microphone, which has an electronically functional component (3a) which is at least partially covered by a cover (3b), wherein the cover is made of a Glob-Top material, the cover has a coefficient of thermal expansion of less than 200 ppm / K, The cover is made of a foamed material.

Description

[0001] The present invention relates to a chip component and a MEMS microphone.

[0002] Reducing the thermoacoustic effect in MEMS microphones is becoming increasingly important to improve the sound quality of these microphones.

[0003] Prior art MEMS architectures are known to use multilayer printed circuit boards with embedded structures such as resistors and capacitors, or printed circuit boards with surface-mounted components. Furthermore, the use of integrated passive components in MEMS microphones, as described in US 10 / 469956 B2 or US 2014 / 0103464 A1, has recently attracted attention.

[0004] Often, such MEMS microphones are positioned near antennas or other devices that can cause unintended interference. This can lead to thermal fluctuations in components such as integrated passive devices. Details on this effect can be found in IEEE Sensors Journal, Vol. 18, No. 13, July 1, 2018, entitled "MEMS Capacitive Microphones: Acoustical, Electrical, and Hidden Thermal-Related Issues" by Germano Nicollini and Daniele Devecchi.

[0005] To insulate integrated passive components against such temperature fluctuations, a cover is often used, which can be applied using, for example, the glob-top technique.

[0006] However, the inventors of the present invention have found that other thermal effects can also contribute to noise generation in such microphones.

[0007] Accordingly, an objective of the present invention is to provide an improved component for a MEMS setup as well as an improved MEMS microphone.

[0008] According to a first embodiment, a chip component is provided for use in a MEMS setup, which is covered with a cover having a coefficient of thermal expansion of less than 200 ppm / K.

[0009] The inventors have found that it is even better if the coefficient of thermal expansion is even smaller, e.g. 100 ppm / K or less, or 50 ppm / K or less.

[0010] In particular, it can be advantageous if the coefficient of thermal expansion is lower than that of standard glob-top materials. Standard glob-top materials can have a coefficient of thermal expansion of 200 ppm / K or more, e.g., 200 to 400 ppm / K.

[0011] The inventors of the present invention have discovered that a heat or temperature change induced in the electronically functional component causes a thermally induced volume expansion of the thermal barrier formed by the cover. This generates pressure on the rear volume of a MEMS microphone.

[0012] Furthermore, the cover material is foamed.

[0013] Using a cover with the properties described above can help reduce thermally induced volume expansion. This can improve the quality of the MEMS microphone.

[0014] The inventors of the present invention have found that it is particularly preferred if the material with the lower coefficient of thermal expansion otherwise exhibits properties of conventional glob-top materials, in particular low stiffness, a thermal conductivity of 0.5 W / m·K or less, and / or a specific heat capacity of over 1000 J / kg·K. Furthermore, the cover material is preferably opaque. These properties are advantageous for reducing thermally induced volume expansion. However, it is not necessary for a cover material to possess all of these properties to achieve the effect according to the invention.

[0015] The volume of the cover can be, for example, between 0.1 mm 3 and 1 mm 3 , such as between 0.2 mm 3 and 1 mm 3 be.

[0016] Preferred materials for the cover according to the invention are materials based on silicone, acrylate, epoxy or anhydride.

[0017] The invention is explained below with reference to exemplary embodiments and measured and simulated simulation data for these embodiments. All representations of exemplary embodiments are not to scale, and no actual sizes or size ratios of components can be derived from the representations of the exemplary embodiments. Fig. Figure 1 shows a schematic representation of a MEMS microphone in a perspective sectional view. Fig. Figure 2 shows a schematic and simplified cross-sectional view of a MEMS microphone. Fig. Figure 3 shows a schematic representation of a MEMS microphone in a transparent perspective view. Fig. Figure 4 shows a diagram. Fig. Figure 1 shows a first embodiment of a MEMS microphone. The MEMS microphone shown has a three-chip configuration.

[0018] The MEMS microphone has a substrate 10 with metal layers 8 for electrical connection. Specifically, the substrate 10 contains four copper layers. Three chips are mounted on the substrate 10: a MEMS chip 1, an ASIC chip 2, and an integrated passive device die (IPD chip 3). A solder mask 5 is applied to the surface of the substrate 10. The MEMS chip 1 is bonded to the substrate 10 via a MEMS adhesive 6. The substrate 10 measures approximately 3 mm × 4 mm, which is also the approximate size of the entire MEMS assembly.

[0019] The substrate 10 has an opening 7 that forms a sound port cavity below the MEMS chip 1. A diaphragm of the MEMS chip 1 is located above the sound opening.

[0020] The ASIC chip 2 is electrically connected to the MEMS chip 1. Furthermore, the ASIC chip 2 is electrically connected to the metal layers 8 in the substrate via wire bonds 9.

[0021] Furthermore, a metallic cover 4 is arranged on the substrate 10 and connected to the surface of the substrate 10 via a cover solder 11. The cover 4 encloses the components arranged on the surface of the substrate 10 and forms a rear volume for the MEMS microphone.

[0022] The IPD chip 3 shown here is an example of a chip component for use in a MEMS setup. It is a silicon-based chip that includes a high-frequency filter circuit. The IPD chip 3 is shown here only as an electronically functional component without a cover to better illustrate the overall MEMS setup. In an arrangement according to the invention, however, it is provided with a cover.

[0023] Fig. Figure 2 shows a second embodiment of a MEMS microphone according to the invention. It is essentially the same MEMS microphone as in Fig. 1, however, with the exception of the IPD chip 3, all components are not explicitly shown to simplify the illustration.

[0024] The IPD chip 3 is arranged on the surface of the substrate, and an underfill 13 is positioned between the electronically functional component 3a and the surface of the substrate 10. The IPD chip 3 comprises an electronically functional component 3a, which is covered by a cover 3b. The cover 3b is a glob-top material with a coefficient of thermal expansion of less than 200 ppm / K. As a specific example, the cover can be made of an epoxy resin such as Loctite Eccobond FP4530. Alternatively, the cover materials can be silicone-based, acrylate-based, epoxy-based, or anhydride-based. Foamed or filled materials can also be used.

[0025] Furthermore, a heat source 12 is depicted in the electronically functional component 3a.

[0026] Cover 3b is able to reduce both the thermoacoustic effect for the rear chamber volume and the thermally induced volume expansion compared to a conventional cover material.

[0027] Fig. Figure 3 shows a microphone model in a transparent view with the same components as in Fig. 1. However, the IPD chip and the ASIC chip are covered by the cover. It is not necessary for the entire surface of the IPD chip to be covered by the cover. In particular, an uncovered volume may exist between the ASIC chip and the IPD.

[0028] In Fig. Figure 4 shows a diagram with combined measured and calculated data. The diagram illustrates the thermally induced pressure caused by a modulation frequency of 217 Hz under standard TDMA conditions. This causes temperature fluctuations originating from the IPD chip 3.

[0029] The black line marked with longer dashed lines, labeled "Thermoacoustic w / o GT," shows the simulated thermoacoustic response curve of a MEMS microphone with an uncovered IPD chip 3. This simulated data is supported by experimental data (data points represented as triangles). The left data point (left triangle) is measured for a first example IPD chip 3 at 3 dBm power dissipation, resulting in a measured thermally induced pressure of 70.9 dBSPL. The right data point (right triangle) is measured for a second example IPD chip 3 at 6 dBm power dissipation, resulting in a measured thermally induced pressure of 76.8 dBSPL.

[0030] The solid line curve labeled "Thermoacoustic with GT" is a first simulation of the thermoacoustic effect with a simulated glob-top coverage, from which a strong improvement in the thermoacoustic effect would be expected when using glob-top.

[0031] However, compared to the experimental data (data points represented by circles), this expectation is not met. The left data point (left circle) is measured for a glob-top of a first example IPD chip 3 at 3 dBm power dissipation, resulting in a measured thermally induced pressure of 34.5 dBSPL. The right data point (right circle) is measured for a second example IPD chip 3 at 6 dBm power dissipation, resulting in a measured thermally induced pressure of 41.5 dBSPL. These values ​​show a considerable improvement over the uncovered IPD chip; however, the results are not as favorable as the simulation suggests, based on the solid curve labeled "Thermoacoustic with GT".

[0032] The inventors of the present invention have determined that the model used for the solid curve labeled "Thermoacoustic with GT" is overly simplified because it does not account for the thermal expansion of the Glob-Top cover. When thermal expansion is taken into account, the curve shown with short dashed lines, labeled "Thermal expansion," is obtained, which corresponds well with the measured data.

[0033] Against this background, the inventors of the present invention set out to provide a cover with a reduced coefficient of thermal expansion in order to come closer to the idealized blue curve called “Thermoacoustic with GT”. Reference character list 1 MEMS chip 2 ASIC chips 3 integrated passive component 3a electronic functional component 3b Cover 4 lids 5 Solder mask 6 MEMS adhesive 7 Opening 8 metal layers 9 Wire bond 10 substrate 11 Lid lot 12 Heat source 13 Underfill

Claims

[1] Chip component for use in a MEMS microphone, which has an electronically functional component (3a) which is at least partially covered by a cover (3b), wherein the cover is made of a Glob-Top material, the cover has a coefficient of thermal expansion of less than 200 ppm / K, The cover is made of a foamed material. [2] Chip component according to claim 1, wherein the cover has a coefficient of thermal expansion of less than 100 ppm / K. [3] Chip component according to claim 1 or 2, wherein the cover has a coefficient of thermal expansion of less than 50 ppm / K. [4] Chip component according to any of the preceding claims, wherein the cover has a coefficient of thermal expansion that is smaller than that of conventional glob-top materials used to reduce a thermoacoustic effect in MEMS microphones. [5] MEMS microphone with the chip component according to one of claims 1 to 4. [6] MEMS microphone according to claim 5, wherein the chip component is an integrated passive component arranged on a substrate of the MEMS microphone.

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