Sensor in a moulded package and a method for manufacturing the same

The flow sensor or other type of sensor comprises a package having a cylindrical section arranged between an anchor section and a head section. The diameter of the anchor section is typically larger than the diameter of the cylindrical section, which in turn is typically larger than the diameter of the head section. A sensor chip is embedded partially into the package, with a sensitive area being exposed to the surroundings. The sensor can e.g. be inserted into a bore having a diameter matching the one of the cylindrical section.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority of European Patent application EP09002618, filed on Feb. 25, 2009 the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The invention relates to a sensor having a moulded package as well as a method for manufacturing the same. In particular, the invention relates to a pressure, flow or substance sensor of this type.

A sensor of this type is disclosed in US 2007/0113648 A1. It comprises a sensor chip embedded in a cuboid moulded package. A window is provided in the package for exposing a sensitive area of the chip to its surroundings. The sensor is designed to measure a parameter, namely humidity, of said surroundings.

Sensors of this type are typically mounted on printed circuit boards, and the printed circuit boards are then located in contact with the surroundings. Alternatively, the sensors are mounted in suitable holders that allow to bring them into contact with the surroundings, in which case the leads of the sensor are either connected to a circuit board located close by or they are connected to connecting wires leading to a remote circuit board.

It is desired to provide a sensor of this type that can be mounted easily for various types of applications.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided a sensor according to claim1. A moulded package of the sensor comprises a cylindrical section. Providing the package with such a cylindrical section makes it, for many applications, much easier to mount the device because it can simply be inserted into a matching cylindrical bore, tube or other type of opening.

In other words, the package combines the purpose of a conventional plastics package (such as acting as a protective coating of the sensor chip) with the purpose of a plug-like mechanical holder suited for insertion into any cylindrical opening with appropriate diameter.

Advantageously, the package further comprises an anchor section which, in at least one direction perpendicular to the axis of the cylindrical section, has a radius exceeding the one of the cylindrical surface. In this case, the anchor section serves as a stop when introducing the package into the opening mentioned above. Advantageously, in all directions perpendicular to said axis, the anchor section has a radius exceeding the radius of the cylindrical section, which allows the anchor section to act as a kind of cap closing the end of the receiving opening.

The sensor is advantageously manufactured by mounting the sensor chip to a lead frame section and placing the lead frame section with the chip into a mould. A hardening package material is then inserted into the mould and hardened. The mould has a cylindrical interior chamber section for forming the cylindrical section of the package.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

The term “radius” as used herein designates the extension of the package from an axis designated by the reference numeral4in the drawings to its surface, in a direction perpendicular to axis4.

The terms “radial” and “axial” refer to the directions perpendicular and parallel, respectively, to the axis4of the sensor.

The “sensor chip” is any integrated sensor on a substrate, such as a silicon substrate or a glass substrate. It has a sensitive area for measuring a parameter of its surroundings. It may e.g. be a substance sensor, i.e. a sensor for measuring the presence and/or amount of a given substance in the surrounding fluid, for example a carbon dioxide sensor or a humidity sensor as described in WO 01/42776. Or it may e.g. be a pressure sensor, such as described in EP 1 860 417 or a flow sensor, such as described in EP 1 840 535.

First Embodiment

The sensor ofFIGS. 1-3comprises a sensor chip1having a sensitive area2. It is moulded partially into a package3, which is typically of a plastics material as known to the skilled person.

Package3has an axis4and, along axis4, package3comprises an anchor section5, a cylindrical section6and a head section7, with cylindrical section6being arranged between anchor section5and head section7.

As can best be seen inFIG. 2, cylindrical section6has a cylindrical outer surface arranged coaxially to axis4. In the shown embodiment, anchor section5and head section7also have substantially cylindrical outer surfaces coaxial to axis4. The shapes of the outer surfaces of anchor section5and head section7may, however, also be non-cylindrical, e.g. rectangular or polygonal.

However, at least in one direction perpendicular to axis4, anchor section5advantageously has a radius R2exceeding the radius R1of cylindrical section6. Thus, it can act as an axial stop when inserting package3into an opening as described above.

Similarly, the radius R3of head section7advantageously does not exceed the radius R1of cylindrical section6, and, in at least one direction, it advantageously has a smaller radius R3than the radius R1of cylindrical section6. Thus, the package can be inserted with head section7first into the opening as described above.

In the embodiment ofFIG. 1, sensor chip1is located at least partially in head section7, and sensitive area2is not covered by package3but rather located in a window formed by a recess8, which is open in radial direction. It is also open axially towards the end of package3that faces away from anchor section5, such that sensitive area2is well exposed to the surroundings.

A protective cap10(only shown inFIG. 1) can be arranged over head section7for protecting the sensor and in particular sensitive area2. Cap10is advantageously provided with axially extending legs11having toe portions12snapped into a groove or recess13extending around head section7.

As shown inFIG. 1, cap10can carry a filter14, e.g. formed by a mesh, a porous material or a semi-permeable membrane in order to prevent unwanted substances or particles from reaching sensitive area2.

As it is also shown inFIG. 1, the sensor advantageously comprises a sealing ring16located in a circumferential recess17and extending around cylindrical section6. The purpose of sealing ring16is to seal the opening into which the sensor has been inserted. In the embodiment as shown, sealing ring16abuts radially e.g. against the inner wall of a surrounding opening or bore. Alternatively, sealing ring16can be arranged to abut axially against e.g. a flat surface surrounding such opening or bore.

As can best be seen fromFIGS. 1 and 3, the sensor further comprises a lead frame section18, typically of a metal. Lead frame section18comprises an “embedded section”, embedded in package3, comprising a die pad19and embedded parts20aof the leads. Lead frame section18further comprises a “contact section” formed by non-embedded parts20bof the leads and not being covered by package3. Contact section20bis exposed for connecting the sensor to other circuitry. Bond wires22connect the embedded parts19of the leads to sensor chip1. Sensor chip1is typically fastened, e.g. glued, to die pad19.

In the embodiment ofFIGS. 1-3as well as in some of the following embodiments, at least part of lead frame section18extends parallel to axis4. In the shown embodiment, axis4even extends through lead frame section18.

The arrangement of lead frame section18parallel to axis4has the advantage that the extension of the sensor along axis4can be arbitrarily large, which allows the sensor to reach deep into the opening that it is mounted in.

As it can also be seen inFIG. 1, sensitive area2is located on a surface of sensor chip1that extends parallel to axis4. Again, this allows sensitive area2to be located deeply within the opening that receives the sensor.

In any embodiment of the present invention, lead frame section18advantageously is located at least partially in anchor section5and its contact section20bextends from anchor section5, thus allowing to connect the sensor from the side of the anchor section.

As can be seen inFIGS. 1 and 3, the sensor shown here comprises, in addition to sensor chip1, a further circuit element25embedded in package3. Circuit element25is e.g. a blocking capacitor and is connected to the ground and supply voltage leads of lead frame section18. It may e.g. be glued or soldered onto lead frame section18. Circuit element25can also e.g. consist of or comprise an integrated processing circuit and/or other active or passive circuitry.

FIGS. 1 and 2show that the outer surface of cylindrical section6may be equipped with structures allowing to fasten the sensor in its opening. In the embodiment ofFIG. 6this is achieved by protrusions27extending away from the cylindrical outer surface of cylindrical section6for forming a bayonet-type coupling.

Similarly, such protrusions28may also form a tangential stop preventing a rotation of the sensor in its opening.

In general, at least one structure on the outer surface of the sensor can be provided for attaching the sensor, e.g. in an opening, and/or for locking the sensor against rotation about axis4.

Second Embodiment

The second embodiment of the device as shown inFIG. 4differs from the first one in that a lead frame section18with a “recessed” die pad19has been used, i.e. die pad19resides in a plane parallel to but offset from the plane of the leads20a,20b. This has the advantage that the leads20a,20bcan be laterally offset in respect to the bottom surface of sensor chip1. In the embodiment ofFIG. 4this is used for placing the leads201,20bas well as the center plane of sensor chip1into axis4.

As it is also illustrated inFIG. 4, a recess30can be formed in package3at a location below sensor chip1. This may be useful whenever an access to the bottom side of sensor chip1is required, e.g. if sensor chip1has been mounted to the lead frame section using “flip chip” technology.

Third Embodiment

In the embodiments shown so far, lead frame section18extends parallel to axis4. The embodiment inFIGS. 5 and 6represents a type of sensor where at least part of lead frame section18extends perpendicularly to axis4. This design has the advantage that it allows to build flatter sensors as well as sensors with radially protruding leads.

The sensor ofFIGS. 5 and 6again has a package3with anchor section5and cylindrical section6, wherein anchor section5has, at least in one direction, a radius larger than the radius of cylindrical section6. The outer surface of cylindrical section6is again coaxial to the axis4of the sensor.

In the third embodiment, lead frame section18is located completely in anchor section5, with sensor chip1being arranged on that side of die pad19which faces cylindrical section6. Sensitive area2is again located in a window formed by a recess8, with recess8opening towards the axial end face of the sensor.

Again, a sealing ring16extends around cylindrical section6for sealingly embedding the sensor in the opening. Sealing ring16arranged to abut in axial direction (i.e. in a direction parallel to axis4) against a surface.

Fourth Embodiment

In the embodiments shown so far, anchor section5has cylindrical circumference.FIG. 7shows an embodiment of the invention where anchor section5has rectangular circumference. Also, as illustrated, anchor section5can be equipped with structures allowing to fasten it to a support, such as a hole32for receiving a screw.

FIG. 7further shows a differently formed recess or window8especially suited for flow measurement.

Fifth Embodiment

In the embodiment ofFIGS. 5 and 6, recess8has to be sufficiently deep to reach all the way to sensitive area2, which makes it necessary to either make cylindrical section6comparatively short or to make recess8comparatively deep.

This potential design drawback is overcome by the fifth embodiment of the device as shown inFIG. 8, where lead frame section18has a non-planar configuration, e.g. by having suitably bent leads20a, such that it reaches into cylindrical section6, thus allowing to mount sensor chip1closer to the end of the sensor and therefore to make recess8more shallow for the same cylindrical section length.

Sixth Embodiment

The leads of lead frame section18, and in particular the exposed parts20bthereof, may also be bent at an angle of approximately 90° such that their ends extend parallel to axis4, while the embedded section20aof the leads as well as die pad19extend perpendicular to axis4. This allows to create a sensor that requires less space in radial direction.

Such an embodiment is shown inFIG. 9.

FIG. 9also shows that a recess30can be formed in package3at a location below sensor chip1and extending through anchor section5. This is e.g. useful for a differential pressure sensor measuring the pressure difference above and below semiconductor chip2.

Seventh Embodiment

FIGS. 12 and 13show a seventh embodiment of a sensor of the present invention.

This embodiment of the sensor substantially corresponds to the one ofFIGS. 1 and 2, but does not comprise an anchor section, thus that it can be inserted deeply into any suitable opening.

FIGS. 12 and 13also show the circumferential groove or recess17for receiving the sealing ring16.

Manufacturing the Sensor

The sensor described here can be manufactured in a substantially conventional transfer mould process, as it is e.g. used for semiconductor packaging.

Typically, a plurality of sensor chips1is first mounted to a lead frame comprising a plurality of lead frame sections18, e.g. by being glued to die pads19of the individual lead frame sections18. Then, they are connected to the leads20a,20bby means of the bond wires22. Also, the circuit elements25can be mounted to the leads20a,20b, e.g. by conducting glue.

In a next step, the assembly of lead frame sections with the sensor chips is placed in a suitable mould. The mould is shaped to form the packages3. A hardening package material is injected into the mould and hardened. Then the mould can be removed. The individual sensors can finally be formed by separating the lead frame sections, e.g. in a punching process.

The mould advantageously has a first mould part and a second mould part with a separating plane between the first and the second mould part extending parallel to the lead frame section.

Recess8can be formed e.g. using the techniques described in WO 2006/114005.

For the embodiments ofFIGS. 4 and 8, a preformed lead frame section can be used. For manufacturing the embodiment ofFIG. 9, the leads20bcan be bent after forming the packages.

Application

As mentioned, the sensor can e.g. be inserted into a cylindrical opening, such as a tube or a bore. This is illustrated inFIG. 10, where the sensor is located in a bore33extending through a wall34, e.g. the wall of a gas channel.

If the sensor is to be used as a flow sensor, an arrangement as shown inFIG. 11can be used. Here, opening33extends through a wall34into a flow channel35, where a fluid is flowing into a direction perpendicular to the plane of the drawing. Head section7of the sensor extends into flow channel35. Cap10is provided with at least two, e.g. opposing, openings39, perpendicular to the plane of drawing, such that the fluid in flow channel35can flow through it and along sensitive area2in well-defined manner.

When the sensor is being used as a flow sensor, recess8is advantageously formed such that the sensitive area2is well exposed to the flowing fluid. This is illustrated inFIG. 2, where the dotted lines38indicate a possible cross section of head section7in such an application. This cross section is elongated with substantially flat sides, wherein sensitive area2is arranged at one of the flat sides.