Lens support and wirebond protector

A wirebond protector has an elongated shape that corresponds to the elongated array of wirebonds along the edge of a microelectronic device that connect a semiconductor die to electrical conductors on a substrate. In making the microelectronic device with wirebond protection, wirebonds are first formed in the conventional manner The wirebond protector is then attached to the device in an orientation in which it extends along the array of wirebonds to at least partially cover the wirebonds.

BACKGROUND

In optical communications networks, optical transmitter modules, optical receiver modules, and optical transceiver modules are used to transmit and receive optical signals over optical fibers. In a transmit portion of such an optical module, a laser generates modulated optical signals that represent data, which are then transmitted over an optical fiber. The laser can be, for example, a Vertical Cavity Surface Emitting Laser (VCSEL) or an edge-emitting laser. In a receive portion of such a module, an optics system directs light propagating out of the end of an optical fiber onto an optical detector or photodetector, which converts the optical energy into electrical energy. An photodetector is typically a semiconductor photodiode device, such as a PIN (p-type/intrinsic/n-type) photodiode. Optical transceiver modules typically include multiple lasers for transmitting multiple data signals and multiple photodiodes for receiving multiple data signals.

An optical module is commonly assembled by mounting the optical device, i.e., laser or optical detector, on a substrate, also referred to as a leadframe. As the optical device typically comprises a microelectronic semiconductor die, electrical connections between the die and conductors on the substrate are made by a technique known as wirebonding. Wirebonding is a technique in which one end of a very fine wire is bonded to a pad on the die using thermal or ultrasonic energy, and the other end is bonded to one of the conductors on the substrate. A lens assembly can be aligned with the transmit or receive optical ports of the die and mounted in fixed relation to the die and substrate.

Wirebonds are extremely fragile because the wires are extremely fine, i.e., thin gauge. Rough handling of the optical assembly can easily break or dislodge a wirebond. In some optical assemblies, the wirebonds are protected by an enclosure or module body that encloses the entire optical assembly. In some assemblies, the wirebonds are encapsulated in a dielectric resin to protect them.

SUMMARY

Embodiments of the present invention relate to a wirebond protector, microelectronic device, and method for protecting wirebonds. The wirebond protector has an elongated shape that corresponds to the elongated array of wirebonds along the edge of a microelectronic device that connect a semiconductor die to electrical connections on a substrate. In making the microelectronic device, the wirebonds are first formed in the conventional manner. The wirebond protector is then attached to the microelectronic device in an orientation in which it extends along the array of wirebonds to at least partially cover and thereby protect the wirebonds.

DETAILED DESCRIPTION

As illustrated inFIGS. 1-5, in an exemplary embodiment, a wirebond protector100has an elongated shape defined by a top wall102and a side wall104. At opposing ends of wirebond protector100are feet106and108that together define a bottom of wirebond protector100. Recesses110and112at the respective ends of wirebond protector100facilitate aligning and attaching wirebond protector100, as described below. It should be noted that the intersection of top wall102and side wall104defines an interior space or cavity114in wirebond protector100.

Wirebond protector100can be made from any suitable material, including plastic, epoxy or other resin, metal, etc. Wirebond protector100can be formed by injection molding, casting, extrusion, or any other suitable conventional processes. Wirebond protector100can be, for example, injection molded from a transparent, semi-transparent, or opaque liquid crystal polymer (LCP).

As illustrated inFIG. 6, a wirebond array116of a microelectronic device assembly118can be protected by attaching wirebond protector100. Wirebond array116comprises multiple wirebonds that extend along an edge of a substrate120. As well understood in the art (and thus not shown in detail for purposes of clarity), each wirebond comprises a fine wire having one end bonded to a pad of a semiconductor die122and another end bonded to a conductor of the substrate120. Wirebond array116is defined by the line of wirebonds, which is commonly straight or linear, as in the illustrated embodiment of the invention, but can alternatively have one or more bends. Note that the elongated shape of wirebond protector100corresponds to or conforms to the elongated shape of wirebond array116. Accordingly, in embodiments in which a wirebond array having a non-linear shape is to be protected, the wirebond protector would have a corresponding or conforming shape. For example, in an alternative embodiment (not shown) the wirebond protector could be L-shaped to protect an L-shaped wirebond array.

In the exemplary embodiment, substrate120comprises a leadframe124and a mounting core125attached to the upper surface of leadframe124. Although the terms “substrate” and “leadframe” are sometimes used interchangeably in the art, the term “substrate” as used in this patent specification (“herein”) is not limited to a leadframe; rather, the term “substrate” broadly includes within its scope of meaning any suitable element or assembly of elements. In the exemplary embodiment, several semiconductor dies122are mounted on substrate120by virtue of being mounted on mounting core125, which in turn is mounted on leadframe124of substrate120. Although in the exemplary embodiment substrate120comprises leadframe124and mounting core125, in other embodiments the substrate can have any other suitable structure.

Semiconductor dies122can comprise any suitable type of device known in the art. For example, they can be optical transmitters (e.g., VCSELs) and receivers (e.g., photodiodes) in an embodiment in which microelectronic device assembly118is part of an optical transceiver module. Although the exemplary embodiment includes multiple semiconductor dies122, some of which are optical transmitters and others of which are optical receivers, other embodiments can have as few as a single die.

Wirebond protector100can be attached to microelectronic device assembly118by moving it generally in the direction of the arrows shown inFIG. 6into alignment with microelectronic device assembly118. As wirebond protector100approaches microelectronic device assembly118, tapered or angled surfaces in recesses110and112guide corresponding protrusions126and128on (mounting core125of) substrate120. Protrusions126and128mate with recesses110and112(seeFIGS. 1,2and5) in a snap engagement or, alternatively, a press-fit (also known as an interference-fit) engagement. This guiding action inhibits portions of wirebond protector100from colliding with a wirebond and damaging it as wirebond protector100is moved into alignment. When wirebond protector100is fully mated with microelectronic device assembly118, feet106and108rest on the surface of (leadframe124of) substrate120to stabilize the structure against undesired movement. Protruding portions of feet106and108also serve as stops, abutting portions of substrate120when wirebond protector100is fully mated with microelectronic device assembly118.

In some embodiments, a suitable adhesive can be used alternatively or in addition to the mechanical mating features described above to secure wirebond protector100to microelectronic device assembly118. Note that although in the exemplary embodiment wirebond protector100attaches to mounting core125, in other embodiments the wirebond protector can attach to any other element or portion of the substrate.

In the exemplary embodiment, two such wirebond protectors100and100′ are attached to opposing edges of substrate120to protect correspondingly opposing wirebond arrays116and116′, as shown inFIGS. 6-10. Note that the individual wirebonds of arrays116and116′ are covered by or semi-enclosed within cavities114and114′, respectively. Although in the exemplary embodiment wirebond protectors100and100′ nearly completely shield or protect wirebond arrays116and116′, in other embodiments it is suitable that the wirebond protector at least partially cover the wirebonds.

It can be seen inFIGS. 6-10that microelectronic device assembly118with attached wirebond protectors100and100′ protects the wirebonds against adverse effects of rough handling. It should be noted that wirebond protectors100and100′ also serve to shield semiconductor dies122and other elements from contaminants such as dirt and dust particles.

In addition to wirebond protector100protecting the wirebonds against damage and shielding the wirebonds and other areas against contaminants, the flat surface of top wall102of wirebond protector100can be used as a mounting or receiving surface for an additional or auxiliary device. As illustrated inFIG. 11, in the exemplary embodiment, in which microelectronic device assembly118is part of an optical transceiver module, such an additional device can be a lens assembly130. As known in the art, optical lenses are commonly included in optical transceiver modules to focus light produced by an optical transmitter such as a VCSEL or focus received light upon an optical detector.

As described above, for example, some or all of dies122can be VCSELs. Lens assembly130can be mounted with its opposing edges on the flat surfaces of upper walls102and102′ of respective wirebond protectors100and100′, with the body of lens assembly130spanning the interior portion of microelectronic device assembly118. Supporting lens assembly130on wirebond protectors100and100′ facilitates optically aligning the lenses (not shown) of lens assembly130with the VCSEL ports (not shown). Epoxy or other suitable adhesive applied to the flat surfaces of top walls102and102′ can be used to secure lens assembly130to wirebond protectors100and100′. As the epoxy is disposed in a plane perpendicular or normal to the optical axes of the VCSEL ports, forces resulting from the curing of the epoxy are not in directions that would tend to pull the lenses of lens assembly118out of optical alignment with the VCSEL ports. Also note that with lens assembly130covering the interior of microelectronic device assembly118, the combination of wirebond protectors100and100′ and lens assembly130further serves to seal the interior against contaminants, especially if epoxy or other sealant is used.

It should further be noted that in embodiments in which wirebond protectors100and100′ are transparent or at least semi-transparent, manufacturing personnel can visually inspect the wirebonds even after wirebond protectors100and100′ have been attached to microelectronic device assembly118, and even after lens assembly130or other such auxiliary device has been attached.

Wirebonds of a microelectronic device can be protected in accordance with the invention by, for example, performing the method illustrated inFIG. 12. As indicated by step132, a wirebond array116is first formed between semiconductor die122and substrate120. As well understood in the art, wirebonding entails bonding one end of a very fine wire to a pad (not shown) on die122using thermal or ultrasonic energy, and bonding the other end of the wire to one of the conductors (not shown) of substrate120.

Various additional steps can be included in some embodiments of the method. For example, as indicated by step134, a resin, adhesive or other material can be applied to a portion of wirebond protector100or to a mating element of semiconductor device assembly118. The material can be used to adhere wirebond protector100to the mating portion of semiconductor device assembly118, to encapsulate the wirebonds, or for other suitable purposes. For example, the material can be applied to the interior or cavity114to encapsulate the wirebonds or to the surface of top wall102to adhere lens assembly130.

As indicated by step136, wirebond protector100is then attached in an orientation that at least partially covers wirebond array116. Two or more such wirebond protectors can be attached in embodiments in which two or more corresponding wirebond arrays are to be protected. As best illustrated inFIGS. 6-10, the wirebonds of arrays116and116′ are thereby enclosed within cavities114and114′, respectively.

As indicated by step138, in embodiments in which an adhesive or other material is applied, the material can be cured to harden or set it. In embodiments in which wirebond protector100is transparent or otherwise transmissive of ultraviolet (UV) light, the material can be a UV light-curable resin or epoxy. Note that the wirebonds can be visually inspected in an embodiment in which both the epoxy and wirebond protector100are sufficiently transparent or clear.

As indicated by step140, in some embodiments an auxiliary device can be mounted on one or more wirebond protectors100. As described above, in the exemplary embodiment lens assembly130is mounted between two wirebond protectors100and100′. Although in the exemplary embodiment this auxiliary device is a lens assembly, in other embodiments it can be any other suitable type of device.

Any suitable conventional steps can also be included, such as mounting the entire assembly in a suitable transceiver module package or enclosure. Also, it should be recognized that not all embodiments need include all of the above-described steps. For example, some embodiments do not include some or all of steps134,138and140. Furthermore, steps can be performed in any suitable order unless explicitly stated otherwise.

One or more illustrative embodiments of the invention have been described above. However, it is to be understood that the invention is defined by the appended claims and is not limited to the specific embodiments described.