Sensor Arrangement and Method for Producing a Sensor Arrangement

Abstract

In an embodiment a sensor arrangement includes a substrate, at least one spacer arranged directly onto a surface of the substrate, wherein the spacer comprises a soft material and a sensor chip attached to the substrate by an adhesive, wherein both the at least one spacer and the adhesive are arranged at least partly between the sensor chip and the substrate, and wherein the spacer is adapted and arranged to define a bond line thickness of the adhesive.

Claims

1. A sensor arrangement comprising: a substrate; at least one spacer arranged directly onto a surface of the substrate, wherein the spacer comprises a soft material; and a sensor chip attached to the substrate by an adhesive, wherein both the at least one spacer and the adhesive are arranged at least partly between the sensor chip and the substrate, and wherein the spacer is adapted and arranged to define a bond line thickness of the adhesive.

2. The sensor arrangement according to claim 1, wherein the at least one spacer comprises the same material or a material with similar elastic properties as the adhesive.

3. The sensor arrangement according to claim 1, wherein the at least one spacer is arranged at the surface of the substrate in form of a line or in form of a bump.

4. The sensor arrangement according to claim 1, wherein the at least one spacer comprises a material supporting UV, light or thermal curing, or wherein the at least one spacer comprises a solvent based material.

5. The sensor arrangement according to claim 1, wherein the at least one spacer comprises a height between 20 μm and 100 μm, inclusive.

6. The sensor arrangement according to claim 1, wherein the at least one spacer comprises a Shore A hardness between 25 and 70, inclusive.

7. The sensor arrangement according to claim 1, wherein a Young's modulus of the at least one spacer is between 1 Mpa and 50 Mpa, inclusive.

8. The sensor arrangement according to claim 1, wherein the adhesive comprises a Shore A hardness between 25 and 70, inclusive, and/or a Young's modulus between 1 Mpa and 50 Mpa, inclusive.

9. The sensor arrangement according to claim 1, wherein a material of the spacer comprises a soft silicone, a soft epoxy, or a modified polycarbamin acid derivate.

10. The sensor arrangement according to claim 1, wherein the sensor arrangement is a MEMS microphone.

11. A method for producing a sensor arrangement, the method comprising: providing a substrate; providing a plurality of spacers and arranging the spacers onto a surface of the substrate in a predetermined pattern; curing a material of the spacers; providing an adhesive and applying the adhesive onto parts of the surface of the substrate; providing a plurality of sensor chips and attaching the sensor chips onto the substrate by the adhesive; curing the adhesive; and separating the substrate into individual components such that the sensor arrangement comprising at least one spacer is formed.

12. The method according to claim 11, further comprising inspecting a height of the spacers before the spacers are arranged on the substrate.

13. The method according to claim 11, further comprising providing and assembling a protection for the sensor arrangement before separating the substrate.

14. The method according to claim 11, wherein the spacers are printed onto the substrate, or wherein the spacers are applied onto the substrate by needle or jet dispensing.

15. The method according to claim 11, wherein curing the material of the spacers comprises curing the material by UV, by light or by thermal curing.

16. The method according to claim 11, wherein the respective spacer is positioned on the surface of the substrate in form of a line or a bump.

17. The method according to claim 11, wherein the material of the respective spacer comprises a soft silicone, a soft epoxy, or a modified polycarbamin acid derivate.

18. The method according to claim 11, wherein the respective spacer comprises a Shore A hardness between 25 and 70, inclusive, and wherein a Young's modulus of the respective spacer is between 1 Mpa and 50 Mpa, inclusive.

19. The method according to claim 11, wherein the respective spacer comprises the same material or a material with similar elastic properties as the adhesive.

20. The method according to claim 11, wherein the adhesive comprises a Shore A hardness between 25 and 70, inclusive, and/or a Young's modulus between 1 Mpa and 50 Mpa, inclusive.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Further features, refinements and expediencies become apparent from the following description of the exemplary embodiments in connection with the figures.

[0049] FIG. 1 schematically shows a top view of a part of a sensor arrangement;

[0050] FIG. 2 schematically shows a top view of a part of a sensor arrangement according to a first embodiment;

[0051] FIG. 3 schematically shows a top view of a part of a sensor arrangement according to a second embodiment;

[0052] FIG. 4 schematically shows a top view of a part of a sensor arrangement according to a third embodiment;

[0053] FIG. 5 schematically shows a top view of a part of a sensor arrangement according to a fourth embodiment;

[0054] FIG. 6 schematically shows a top view of a sensor arrangement; and

[0055] FIG. 7 schematically shows a sectional side of the sensor arrangement according to FIG. 6.

[0056] In the figures, elements of the same structure and/or functionality may be referenced by the same reference numerals. It is to be understood that the embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0057] FIGS. 1 to 5 show parts of a sensor arrangement 1 in different embodiments. FIGS. 6 and 7 show a complete sensor arrangement 1 in a first embodiment.

[0058] The sensor arrangement 1 is a MEMS sensor arrangement. In particular, the sensor arrangement 1 is a MEMS microphone.

[0059] The sensor arrangement 1 comprises a substrate 2. The substrate 2 is square shaped. Of course, other shapes are also conceivable for the substrate 2. For example, the substrate 2 may be shaped rectangularly. The substrate 2 comprises a hole 6 which is adapted and arranged to serve as acoustic access for the microphone. The hole 6 is arranged in a central area of the substrate 2. The hole 6 completely penetrates the substrate 2, as can be gathered from FIG. 6, for example.

[0060] The sensor arrangement 1 further comprises a sensor chip 5 (see FIGS. 6 and 7). The sensor chip 5 comprises a cavity 7. The cavity 7 is arranged in a central region of the sensor chip 5. The cavity 7 may be an oval or circular or hexagonal hole which penetrates the sensor chip 5 completely. On an upper side of the sensor chip 5 (i.e. that side which is arranged furthest away from the substrate 2 once the sensor chip 5 is attached to the substrate 2), a membrane is attached to the sensor chip 5 for covering the cavity 7 (not explicitly shown).

[0061] The sensor chip 5 is attached to the substrate 2 by means of an adhesive 4. The adhesive 4 may comprise a silicone material or similar materials. Alternatively, the adhesive may comprise a closed-cell polymer foam. The adhesive 4 acts as a bond line between the substrate 2 and the sensor chip 5.

[0062] The adhesive 4 is applied to a surface of the substrate 2 in a predetermined pattern or geometry, which is adapted to a shape of the sensor chip 5 and, in particular, to a shape and size/diameter of the cavity 7. The adhesive 4 is applied to the substrate 2 such that the adhesive 4 does not or only slightly cover the cavity 7 in the sensor chip 5 (see FIG. 6). The adhesive 4 may be applied such that it covers an outer edge area of the sensor chip 5.

[0063] In the embodiments shown in FIGS. 3 and 4, the adhesive 4 is applied to the substrate in the shape of a square with rounded corners. Of course, alternative geometries are conceivable for the adhesive 4 which depend, for example, on the material of the adhesive and/or on the shape of the sensor chip 5. For example, the adhesive 4 may be applied in the shape of an Octagon (FIGS. 2, 5 and 6). Usually, the shape of the adhesive 4 is closed to achieve an air-tight seal.

[0064] Depending on the geometry of the bond line, it may be advantageous to select also non-silicone material as adhesive 4. The reason is the inappropriate Poisson's ratio of close to 0.5 for silicones. As a consequence, they can change their shape virtually not by compressibility or expandability, but only by transverse contraction. But the latter may be significantly inhibited by the aspect ratio of a wide and narrow bond gap, so the joint behaves tough even though a low modulus adhesive is used. In that case, the Poisson's ratio should be <0.49, preferably <0.48, more preferably <0.45, most preferably <0.42.

[0065] The sensor arrangement 1 comprises at least one spacer 3.

[0066] The respective spacer 3 defines a bond line thickness or height H of the adhesive 4. A sufficiently high bond line thickness H is needed to improve stress decoupling of the sensor arrangement 1. In this context, the bond line thickness H of the adhesive 4 denotes the expansion of the adhesive 4 perpendicular to the surface of the substrate 2 onto which the adhesive 4 is applied.

[0067] The respective spacer 3 has a height between 10 μm and 300 μm, preferably between 20 μm and 100 μm, for definition of the final bond line thickness. The application of the respective spacer 3 can be done by needle or jet dispensing, or by a printing method like stencil or screen printing, which is described later on in more detail.

[0068] The respective spacer 3 is arranged directly onto the substrate 2 before adhesive 4 is applied to the substrate 2, i.e. it is pre-applied to the substrate 2. In particular, the spacers 3 are applied on a surface, i.e. an upper surface, of the substrate 2. In this context, the upper surface of the substrate 2 denotes that surface which is arrange closest to the sensor chip 5 once the sensor chip 5 is attached to the substrate 2. The respective spacer 3 is applied on a footprint for the sensor chip 5. The respective spacer 3 may be at least partly surrounded with adhesive 4 (see, for example, FIG. 4).

[0069] In the embodiment shown in FIGS. 1, 2, 3, 5, 6 and 7, the sensor arrangement 1 comprises four spacers 3. The respective spacer 3 may comprise the form of a spherical segment or bump (FIGS. 1, 2, 5, 6 and 7). Alternatively, the respective spacer 3 can comprise the form of a short line (FIG. 3). The short lines can be aligned to the centre area of the substrate 2 (FIG. 3).

[0070] The sensor arrangement 1 can also comprise more than four spacers 3, e.g. six or eight spacers 3 (not explicitly shown). The sensor arrangement 1 can also comprise less than four spacers 3, e.g. one or two spacers 3 (see, for example, FIG. 4). For example, in the embodiment illustrated by FIG. 4, exactly one spacer 3 is applied to the substrate 2. The said spacer 3 comprises the form of a square with rounded corners. The single spacer 3 comprises a continuous line. In this embodiment, the line shaped spacer 3 is completely surrounded by adhesive 4.

[0071] The respective spacer 3 comprises a soft material. In this context a soft material is understood to be softer than glass material. The respective spacer 3 comprises the same material or a material with similar elastic properties as the adhesive 4. The respective spacer 3 comprises a material supporting UV, light or thermal curing. Alternatively, the spacer 3 can comprise a solvent based material. For example, the spacer 3 comprises a soft silicone, a soft epoxy, or a modified polycarbamin acid derivate.

[0072] The Young's modulus of the cured spacer material is in a range of 0.1 to 200 Mpa, preferably 1 to 50 Mpa. Such soft materials are frequently specified rather by Shore A hardness. The shore A hardness of the spacer material is in a range of 15 to 80, preferably 25 to 70.

[0073] By means of the soft profiled spacer 3, the final bond line thickness H of the adhesive 4 is controlled in a simple and effective way. Thus, stress decoupling for the sensor arrangement 1 is effectively ensured.

[0074] In the following a method for producing a sensor arrangement 1, in particular the previously described MEMS microphone, is described. The method comprises the following steps:

[0075] In a first step A) a substrate 2 is provided. The substrate 2 is a MEMS substrate. The substrate is adequately dimensioned to produce a plurality, e.g. hundreds or thousands, of sensor arrangements. The substrate may comprise a multilayer laminate with metal contact patterns on top and bottom surface. The substrate may further comprise internal electrical interconnections. Additional layers like platings or solder masks may be integral parts of the substrate.

[0076] In a second step B) a plurality of spacers 3 are provided. The spacers 3 comprise a soft material, e.g. a soft silicone, a soft epoxy, or a modified polycarbamin acid derivate.

[0077] Optionally, a height inspection (profile measurement) of the spacers 3 may take place.

[0078] Afterwards, the spacers 3 are arranged onto the surface of the substrate 2 in a predetermined geometry. The geometry depends on the design of the sensor chip 5, the design of the substrate 2, the material of the spacer 3, the material of the adhesive 4, and/or the desired height of the bond line. The spacers 3 are arranged on the surface of the substrate 2 in the form of bumps or lines, for example.

[0079] A preferred spacer arrangement may consist of four laterally relatively small dots or bumps, the distance between two of them being typically larger than ⅓ of a length of a neighboring die edge.

[0080] The spacers 3 can be printed onto the surface of the substrate, e.g. by stencil or screen printing. Alternatively, the spacers 3 can be applied onto the substrate 2 by means of needle or jet dispensing.

[0081] Printing methods are suitable, since package substrates for MEMS microphones typically comprise a plurality of individual units in a large panel that is separated at the end of the assembly, usually after covering the units with a plurality of caps. Therefore, a single printing step can form hundreds or thousands of spacers 3 of high homogeneity.

[0082] In a next step C) a UV, light or thermal curing step can take place for curing the spacer material.

[0083] By using a material for the spacers 3 that supports light or UV curing (complete or to a certain degree), the spread can easily be stopped right after the deposition by suitable illumination, independently of the deposition method (i.e. printing or dispensing). This UV or light curing can be done for a plurality of spacers 3 when applied in a parallel process like printing, or for each individual spacer 3 immediately after deposition in case of a serial process like dispensing. Here, curing of a plurality of spacers is also an option.

[0084] But also thermally curable or even solvent based materials are appropriate for the spacers 3, since only very little volume is required, so that the spread is limited. For the same reason, it is also possible to use material with a very high viscosity (e g. >100 Pa.Math.s) without sacrificing process speed.

[0085] In a next step D) an adhesive 4 is provided. The adhesive 4 is applied onto parts of the surface of the substrate 2 such that the adhesive 4 is arranged at least partly between the sensor chip 5 and the substrate 2. Adhesive 4 may also be applied onto a surface of the respective spacer 3.

[0086] The adhesive 4 is applied in a predetermined pattern. The pattern depends on the design of the sensor chip 5, the material of the spacer 3, the material of the adhesive 4, and/or the desired height of the bond line. For applying the adhesive 4, conventional mass production methods such as jet dispensing, printing or dispensing are used.

[0087] The respective spacer 3 and the adhesive 4 may comprise the same material or a material with similar elastic properties. The adhesive 4 comprises a Shore A hardness between 15 and 80, preferably between 25 and 70. A Young's modulus of the adhesive is between 0.1 Mpa and 200 Mpa, preferably between 1 Mpa and 50 Mpa.

[0088] In a next step E) a plurality of sensor chips is provided. The sensor chips 5 are attached onto the substrate 2 by means of the adhesive 4. The sensor chips 5 can be placed relatively rough and fast without compromising the bond line thickness accurateness.

[0089] In a step F), the adhesive 4 is cured.

[0090] After curing the adhesive 4, additional components may be assembled before a separation into individual components (see step G)) takes place. For example, an ASIC may be assembled. In addition, internal electrical connections, e.g. wire bonds and/or a glob top application may be provided.

[0091] Furthermore, a protection for the sensor arrangement 1 is provided. For example, a cover of the respective sensor arrangement 1, e.g. a metal cap, is provided and assembled.

[0092] In a last step G) the substrate 2 comprising the spacers 3, the adhesive 4 and the sensor chips 5 is separated into individual components such that a plurality of sensor arrangements 1 each comprising at least one spacer 3 is formed.

[0093] Although the invention has been illustrated and described in detail by means of the preferred embodiment examples, the present invention is not restricted by the disclosed examples and other variations may be derived by the skilled person without exceeding the scope of protection of the invention