Packaged die and assembling method

Abstract

In an embodiment A package includes a casing having an opening and enclosing a cavity, a die accommodated in the cavity and a membrane attached to the casing, the membrane being air-permeable, covering and sealing the opening, wherein the membrane is configured to allow only a lateral gas flow, and wherein a blocking member is configured to block a vertical gas flow through the membrane into the cavity, the blocking member tightly covering a surface of the membrane at least in an area comprising the opening.

Claims

1. A package comprising: a casing having an opening and enclosing a cavity; a die accommodated in the cavity; and a membrane attached to the casing, the membrane being air-permeable, covering and sealing the opening, wherein the membrane is configured to allow gas to flow into the cavity mainly in a lateral direction, and wherein a blocking member tightly covers a surface of the membrane vertically adjacent to the opening so that the blocking member is configured to block a vertical gas flow through the membrane towards the blocking member.

2. The package of claim 1, wherein the casing comprises a substrate and a lid joined together, thereby enclosing the cavity.

3. The package of claim 2, wherein the opening is formed between the substrate and the lid.

4. The package of claim 2, wherein the opening is formed in the substrate or in the lid.

5. The package of claim 1, wherein the blocking member is the die.

6. The package of claim 1, wherein the blocking member is part of the casing.

7. The package of claim 1, wherein the membrane is hydrophobic.

8. The package of claim 1, wherein the membrane consists essentially of polytetrafluorethylene (PTFE).

9. The package of claim 1, wherein the die comprises a micro-electromechanical structure (MEMS) or an application-specific integrated circuit (ASIC).

10. The package of claim 2, wherein the substrate comprises a ceramic material or a laminate.

11. The package of claim 2, wherein the lid consists essentially of metal.

12. The package of claim 2, wherein the lid and the substrate are connected by a connecting member and fix the membrane by squeezing it there between.

13. The package of claim 2, wherein bonding pads on the surface of the die are electrically and mechanically connected to respective contacts on the substrate by a fixing member.

14. The package of claim 13, wherein the membrane is arranged between the die and the substrate, and wherein the membrane comprises recesses accommodating the fixing members connecting the bonding pads and the substrate.

15. A method for assembling a package, the method comprising: providing a die comprising bond pads; providing a substrate and a lid, both being part of a casing that encloses a cavity, wherein the lid comprises an open side; arranging a membrane onto a surface of the substrate; arranging the die in the casing; and attaching the substrate with attached membrane on the open side of the lid such that the membrane covers an opening between the substrate and the lid thereby closing the casing and enclosing the die.

16. The method of claim 15, further comprising: forming recesses in the membrane, wherein the membrane is arranged at the substrate; filling of the recesses with fixing members comprising a conductive material; and arranging the die on the fixing members so that the die is mechanically fixed and electrically connected to the substrate.

17. The method of claim 15, wherein the membrane covers the whole surface of the substrate, wherein the substrate and the lid are attached by connecting members, and wherein attaching the substrate and the lid comprises: forming recesses for the connecting members in the membrane, filling the recesses to form the connecting members, and fixing the lid to the connecting members.

18. A method for assembling a package, the method comprising: providing a die comprising bond pads; providing a substrate and a lid, both being part of a casing that encloses a cavity, wherein the substrate comprises an opening; arranging a membrane on the substrate such that the membrane covers the opening in the substrate; arranging the die in the casing; and arranging the lid on the substrate to close the casing, thereby enclosing the die.

19. The method of claim 18, wherein arranging the die at the substrate comprises: forming recesses in the membrane arranged at the substrate, filling the recesses with fixing members comprising conductive material, and arranging the die on the fixing members so that the die is mechanically fixed and electrically connected to the substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following the invention will be explained in more detail with reference to preferred embodiments and their relating figures. The figures are schematically drawn only for better understanding and are not drawn to scale. Identical or equivalent parts are referenced by the same reference symbols. Possible embodiments are not limited to the embodiments disclosed.

(2) FIG. 1A shows in a cross-sectional view a first embodiment of the package;

(3) FIG. 1B shows a top view of an open-topped substrate of the first embodiment of the package;

(4) FIG. 2A shows in a cross-sectional view a second embodiment of the package with the die electrically contacted by the flip-chip method;

(5) FIG. 2B shows in a cross-sectional view a second embodiment of the package with the die electrically contacted by a wire bond;

(6) FIG. 2C shows a top view of an open-topped substrate of the second embodiment of the package with the die electrically contacted by a wire bond;

(7) FIG. 3 shows in a cross-sectional view a third embodiment of the package with the die electrically contacted by a flip-chip method and the membrane positioned between die and substrate;

(8) FIG. 4 shows in a cross-sectional view a fourth embodiment of the package with the die electrically contacted by a wire bond and the membrane positioned between the die and the substrate;

(9) FIG. 5A shows a fifth embodiment of the package with an opening in the substrate covered by a membrane and attached on a printable circuit board with the die electrically contacted by solder balls; and

(10) FIG. 5B shows a fifth embodiment of the package with an opening in the substrate covered by a membrane and attached on a printable circuit board with the die electrically contacted by a wire bond.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(11) FIG. 1A shows, in a cross-sectional view, a first embodiment of the package 1 according to embodiments. The package comprises a casing 2. The casing 2 consists of two separated parts. A substrate 7 comprises the bottom side and the four lateral sides of the casing formed as a box. The substrate 7 may consist of a ceramic material.

(12) The second part of the casing 2 is a lid 8 forming the upper side of the casing 2. The lid 8 may consist of a metallic material. The lid 8 is shaped accordingly to fit on the substrate 7 from the top. Between the substrate 7 and the lid 8 a cavity 9 is formed enclosed by the casing 2.

(13) Between the upper edge of the substrate 7 and the lid 8 a membrane 5a is arranged acting as an interposer between the substrate 7 and the lid 8. The membrane is air-permeable and fills a gap 3 left for air supply to the cavity.

(14) The membrane 5a consists of extended polytetrafluorethylene (PTFE) polymer. For example a TEMISH® membrane may be used. The membrane 5a comprises at least 1 million micropores per square centimeter. Therefore air-permeability is guaranteed. Because of the small diameters between 0.1 μm and 10 μm of the micropores the membrane 5a restrains dust particles and liquids.

(15) The membrane 5a is fixed by gluing it by an adhesive 5b to the substrate 7 and the lid 8. Herein the lid 8 acts as a blocking member 6 to block a vertical gas flow. Only a lateral gas flow (fat arrow) through the gap 3 is possible thereby passing the membrane 5a between the substrate 7 and the lid 8 laterally that is within the plane of the membrane. Therefore the membrane 5a has two functions.

(16) On the one hand, the membrane acts as an interposer leaving a kind of a gap 3 in the casing 2 which allows an air flow from the environment into the cavity 9. On the other hand, the membrane 5a acts as a seal restraining liquids and dust from entering the package 1.

(17) A MEMS die 4 is accommodated in the cavity 9. The MEMS die 4 may act as sensor. The sensor may be a gas sensor, a pressure sensor or a humidity sensor. For exact and sensitive measurements a sufficiently large gas flow from the environment into the cavity 9 is necessary.

(18) For providing electrical contact means the MEMS die 4 comprises a bonding surface with bond pads. The bond pads are connected with the substrate 7 by a wire bond boa. For mechanical fixation the die may be mounted to the bottom of the substrate 7 by a fixing member, an adhesive tape or an adhesive layer 10b.

(19) Since the air or gas to be sensed enters the package 1 on a lateral side the gap 3 may be designated as side port.

(20) In further embodiments, the die 4 may be an ASIC or may comprise both a MEMS and an ASIC.

(21) FIG. 1B shows a top view of the first embodiment of the package with an open-topped substrate 7. The membrane 5a and the lid 8 are omitted in this figure for better clarity. In this example, four wire bonds boa are used to connect the die 4 with the substrate 7.

(22) FIG. 2A shows, in a cross-sectional view, a second embodiment of the package 1 comprising a casing 2 with two parts one of which is the substrate 7 and the other is the lid 8. Substrate 7 and lid 8 may be designed like in the first embodiment. The gap 3 between the substrate 7 and the lid 8 is formed and filled by the membrane 5a acting as an interposer. The membrane 5a further seals the gap 3 against dust and liquids. The membrane 5a is fixed by an adhesive 5b to the substrate 7 and the lid 8.

(23) Since the upper surface of the membrane 5a is blocked by the lid 8 acting as blocking member 6, again no vertical gas flow is possible. Only a lateral gas flow arises. Connecting members 12 like solder bumps or alternatively adhesive bumps are applied on the upper edge of the substrate 7 with a regular distance of around 100 μm between each two bumps. These bumps 12 fix the lid 8 to the substrate 7 thereby squeezing the membrane 5a between the substrate 7 and the lid 8. In this case, no adhesive need to be used to fix the membrane surface at the lid 8. By tightening the membrane 5a by squeezing, the tightness and thus the sealing of the membrane 5a can be improved. However, the membrane 5a can additionally be fixed by an adhesive.

(24) In this embodiment, the connecting member 12 applied as adhesive or solder bumps penetrate the membrane 5a periodically. The penetration is realized by cutting recesses in the membrane 5a which may be filled with an adhesive or solder. The recesses may be cut with a laser.

(25) In the second embodiment, a MEMS die 4 is accommodated in the cavity 9 formed by the casing 2. The die 4 may be electrically contacted by the flip-chip method. This means that the bonding surface of the die with the bond pads for electrical connection is flipped to the bottom. Thus the bonding surface of the die is facing the bottom surface of the substrate 7. Fixing members 11 made of solder or a conductive adhesive are formed on the bond pads of the die 4 and connect the die electrically with the substrate 7. Furthermore the fixing members 11 mount the die 4 mechanically on the surface of the substrate 7.

(26) Alternatively, the die 4 may be electrically contacted by a wire bond boa as shown in FIG. 2B like in the first embodiment. In this case, the die 4 is mechanically fixed to the surface of the substrate 7 by an adhesive layer bob.

(27) FIG. 2C shows a top view of the second embodiment as shown in FIG. 2B. The substrate 7 is open-topped. The die 4 and the lid 8 are omitted for better clarity. Four wire bonds boa may be used to electrically contact the die 4.

(28) In the second embodiment, the die 4 can act as a sensor, in particular as a sensor measuring pressure, gas or humidity.

(29) FIG. 3 shows, in a cross-sectional view, a third embodiment of the package 1 with a gap 3 in the casing 2 at its lateral side like in the first and second embodiment. In the third embodiment the lid 8 is formed as a box and comprises or may consist of a metallic material. The lid 8 forms the upper side and the four lateral sides of the box and hence, of the casing.

(30) As a second part of the casing 2 a substrate forms the bottom of the casing 2. The substrate may consist of a laminate. The substrate is shaped accordingly to fit to the opening of the lid 8 that a cavity 9 is enclosed between the lid 8 and the substrate 7.

(31) Between the lower edge of the lid 8 and the substrate 7 the gap 3 is left. The gap 3 is caused by the membrane 5a acting as an interposer.

(32) In spite of its vertical permeability no vertical gas flow arises in the membrane 5a since its lower surface is blocked by the substrate 7 acting as a blocking member 6.

(33) Similar as in the recent embodiments, the membrane 5a is fixed by an adhesive 5b to the substrate 7 and the lid 8.

(34) Accommodated in the cavity 9 is a die 4. The die corresponds to the die of the second embodiment. In order to mechanically fix and electrically contact the die 4 with the substrate 7, solder bumps are positioned as fixing members 11 between the bond pads on the die surface and bond pads on the substrate 7.

(35) Since the membrane 5a is positioned between the substrate 7 and the die 4, recesses are formed in the membrane 5a and the adhesive 5b between membrane and substrate. The recesses are positioned and formed accordingly to accommodate the fixing members 11 at the desired positions. Once the recesses are formed solder is filled into the recesses. Thus the resulting solder bumps 11 are positioned accordingly to connect the substrate 7 and the die 4 electrically. Furthermore the die 4 is fixed by the solder bumps 11 mechanically.

(36) In one method, the recesses in the membrane 5a are formed before arranging the membrane on the substrate 7.

(37) The die 4 may act as a sensor, in particular a pressure, humidity or gas sensor. Instead of solder an adhesive may be used for the fixing and contacting members 11 and 12.

(38) FIG. 4 shows, in a cross-sectional view, a fourth embodiment of the package 1. The fourth embodiment resembles the third embodiment of the package 1. The package 1 comprises a casing 2 comprising a lid 8 and a substrate 7. The substrate 7 comprises the bottom of the casing 2. The box-shaped lid 8 comprises the upper side and the four lateral sides of the case 2 and comprises an open side at the bottom. Between the lid 8 and the substrate 7 a cavity 9 is formed.

(39) The cavity 9 accommodates a MEMS die 4. Between the substrate 7 and the lid 8 a gap 3 is caused by a membrane 5a acting as an interposer and fixed by an adhesive 5b to the substrate 7 and the lid 8. The membrane 5a seals the package 1 against water and dust from the environment. The die 4 is fixed by an adhesive tape 10b to the membrane 5a.

(40) In contrast to the third embodiment the die 4 is electrically contacted by a wire bond boa connecting the die 4 with the substrate 7. Therefore the wire penetrates the membrane 5a and the adhesive 5b.

(41) Since the membrane 5a is positioned between the lid 8 and the substrate 7 it also acts as mechanical decoupling component reducing thermomechanical stress and bending stress in the casing 2.

(42) FIG. 5A shows, in a cross-sectional view, a fifth embodiment of the package 1. In contrast to the previous embodiments the fifth embodiment of the package 1 comprises a bottom port. A bottom port means that a measured media enters the package 1 from the bottom side.

(43) The package 1 comprises a casing 2 which comprises a box-shaped lid 8 and a substrate 7. The lid 8 comprises an upper side and four lateral sides. It has an open side at the bottom. The substrate 7 comprises the bottom of the casing 2 and provides an opening 16 that may be arranged in the center of the substrate. The opening 16 may be shaped as a circle. The lid 7 and the substrate 8 are tightly fixed together by solder. Alternatively the lid 7 may be attached by a conductive epoxy resin to the substrate 8. The tight attachment of the lid 7 on the substrate 8 improves the RF immunity of the package 1.

(44) The membrane 5a covers the opening 16 in the substrate 7 from the top. The membrane 5a is attached at the substrate 7 by an adhesive 5b surrounding the edge of the opening 16. The die 4, which is a MEMS, is arranged on the upper surface of the membrane 5a acting as a blocking member to block a vertical gas flow from the opening through the membrane 5a into the cavity 9 enclosed between lid and substrate. Therefore only a lateral gas flow through the membrane 5a is possible. Arrows indicate the gas flow that passes through the opening 16 into the membrane 5a and laterally within the membrane 5a into the cavity 9.

(45) The die 4, whose bonding surface faces the substrate 7, is electrically connected to respective contacts on the substrate 7 by solder bumps as fixing members 11. Therefore recesses are cut by laser into the membrane 5a and the adhesive 5b and are filled with solder material. The solder bumps 11 connect the bond pads on the bonding surface of the flipped die 4 with the substrate 7 electrically and fix the die 4 mechanically.

(46) Alternatively, the die 4 may be electrically contacted to the substrate 7 by a wire bond boa as shown in FIG. 5B, similar to the first embodiment. In this case, the die 4 is mechanically fixed to the surface of the membrane 5a by an adhesive layer 10b.

(47) The substrate 7 is mounted on a carrier 13 like for example a printed circuit board (PCB). The carrier 13 may consist from several components, which are adhesively attached. The substrate 7 is mounted on the carrier by a soldering or a conductive adhesive 14. To enable gas supply the carrier 13 comprises an opening 15 which is positioned under the opening 16 in the substrate 7. The substrate 7 and the carrier 13 are tightly attached by the conductive adhesive or the soldering 14 through which no gas supply is possible.

(48) The gas analyzed by the MEMS die 4 acting as a sensor enters the package 1 through the opening 15, flows through the opening 16 and penetrates the membrane 5a in a lateral stream reaching the cavity 9. The carrier 13 may be a part of an electronical device like a mobile phone, smart watch or a navigation device. The described bottom port approach simplifies the assembly and the sealing of the package including the carrier.

(49) The fifth embodiment may be configured to act as a microphone. Therefore a separated back volume is required as a reference volume for the sound detection. Therefore a continuous ring of solder is arranged between the substrate 7 and the die 4 instead of the fixing members 11. The continuous ring acts as seal separating the back volume in the cavity 9 from the environment. Thus no gas flow between the environment and the cavity 9 is possible.

(50) If the MEMS die 4 is configured as a microphone it comprises a functional opening connected with the back volume of the cavity 9. This functional opening is centrally positioned above the opening 16 and covered by a membrane for sound detection. This membrane is configured as an acoustic seal. The ambient acoustic waves enter the sensor through the opening 16. The waves penetrate the membrane 5a covering the opening 16 to be detected by the acoustic sealed membrane. No gas flow into the cavity 9 is possible. Furthermore the membrane 5a restrains undesired liquids or dust particles before reaching the microphone.

(51) The microphone may further comprise an ASIC, which is a small semiconductor die that supports and controls the function of the MEMS.

(52) Notwithstanding the number of exemplary embodiments, the invention is not restricted to the shown embodiments. The die may be any kind of sensing die. The scope of the invention shall only be limited by the wording of the claims.