ENCAPSULATED WAFER-LEVEL CHIP SCALE (WLSCP) PEDESTAL PACKAGING
Consistent with an example embodiment, there is semiconductor device assembled to resist mechanical damage. The semiconductor device comprises an active circuit defined on a top surface, contact areas providing electrical connection to the active circuit. There is a pedestal structure upon which the active circuit is mounted on an opposite bottom surface; the pedestal structure has an area smaller than the area of the active device. An encapsulation, consisting of a molding compound, surrounds the sides and the underside of the active device and it surrounds the contact areas. The encapsulation provides a resilient surface protecting the active device from mechanical damage. A feature of the embodiment is that the contact areas may have solder bumps defined thereon.
This application claims the benefit of U.S. Provisional Application No. 61/708,188 filed on Oct. 1, 2012 and U.S. Provisional Application No. 61/826,307 filed on May 22, 2013 and are incorporated by reference in their entirety.
FIELDThe embodiments of the present invention relate to semiconductor device packaging and, more particularly, to WLCSP packaging having modifications that enhance the manufacturability and quality of products using these WLCSP.
BACKGROUNDThe electronics industry continues to rely upon advances in semiconductor technology to realize higher-function devices in more compact areas. For many applications realizing higher-functioning devices requires integrating a large number of electronic devices into a single silicon wafer. As the number of electronic devices per given area of the silicon wafer increases, the manufacturing process becomes more difficult.
The packaging of an IC device is increasingly playing a role in its ultimate performance. For example, in mobile devices (i.e., mobile phones, tablet computers, laptop computers, remote controls, etc), WLCSP components are used in their assembly. WLCSP components save valuable space in the mobile device. After assembly, in some example processes, customers encapsulate these WLCSP devices by injection molding or casing. This manual post-processing of the WLCSP may result in the device being damage. Consequently, the customer may prefer to have the WLCSP product surrounded by non-brittle material, which prevents damage to the die itself, before receiving the product for assembly in to his mobile device.
There is a need for a WLCSP assembly process which can address the challenges raised by the needs of mobile applications.
SUMMARYThe present disclosure has been found useful in the packaging of semi-conductor devices which find their way into portable electronic devices. In particular, WLCSP products which are furnished as unpackaged die to manufacturers of mobile devices, who in turn encapsulate these devices directly onto a printed circuit board (in an effort to conserve valuable space in the mobile device) may subject these unpackaged die to rough handling. The handling may result in cracking or other latent damage which may not show up until the mobile device reaches the end user.
The unpackaged die are encapsulated in a resilient material, such as an epoxy molding compound which absorbs the shocks of manual handling during assembly of the mobile device. The process can also be used for CSP with or without solder bumps.
In an example embodiment, there is a method for assembling a wafer level chip scale processed (WLCSP) device having solder balls defined thereon, the method comprises, defining a pedestal mounting strip per WLCSP device die thickness and surface area, the pedestal mounting strip have a topside and an underside. The pedestal mounting strip is fabricated out of a molding compound; the pedestal mounting strip has a grid of pedestals on the topside, each one of the grid pedestals has a surface area smaller than the surface area of the back-side of the WLCSP device. The WLCSP device is die attached onto the surface of each one of the grid pedestals, the WLCSP device forms an overhang on each one of the grid pedestals. Each one of the the WLCSP devices on the pedestal mounting strip is encapsulated. The process assures that the encapsulant surrounds the WLCSP devices and flows under the overhang of each WLSCP device.
In another example embodiment, a semiconductor device is assembled to resist mechanical damage, the semiconductor device comprises an active circuit that has solder bumps defined on a top surface, these solder bumps provide electrical connection to the active circuit. There is a pedestal structure upon which the active circuit is mounted on an bottom surface, the pedestal structure has an area smaller than the area of the active device. An encapsulation, consisting of a molding compound, surrounds the sides and the underside of the active device and surrounding the solder balls. The encapsulation provides a resilient surface protecting the active device from mechanical damage.
In an example embodiment, a method for assembling a WLCSP semiconductor device having contact areas defined thereon comprises, defining a pedestal mounting strip per semiconductor device die thickness and surface area, the pedestal mounting strip have a topside and an underside. The pedestal mounting strip is fabricated out of a molding compound, the pedestal mounting strip having a grid of pedestals on the topside, each one of the grid pedestals having a surface area smaller than the surface area of the underside of the semiconductor device. The semiconductor device is die attached onto the surface of each one of the grid pedestals, the semiconductor device forming an overhang on each one of the grid pedestals. With a release foil, the contact areas are protected before encapsulating each one of the WLCSP devices. Each one of the semiconductor devices on the pedestal mounting strip is encapsulated, the user assures the encapsulant surrounds the semiconductor devices and flows under the overhang of each semiconductor device. After encapsulating each one of the WLCSP devices, the release foil is removed. In the corresponding position of the underside of the pedestal mounting strip, each one of the semiconductor devices is marked.
In another example embodiment, there is a method for assembling wafer level chip scale processed (WLCSP) devices from a wafer substrate having a front-side surface upon which solder bumps are defined on active device die and an opposite back-side surface. The method comprises, applying a protection tape on the front-side surface; sawing with a “V-shaped” blade of a first kerf, on the back-side surface of the wafer substrate, in areas corresponding to saw lanes of the active device die, to a depth of about 50% of the wafer substrate thickness; continuing the sawing of the back-side surface with a blade of a second smaller kerf, so as to separate the active device die into singulated device die, wherein each of the singulated device die has an angled recessed profile with respect to the vertical faces of the device die; remounting the singulated device die on their front-side surfaces onto a sawing tape; die bonding the singulated device die onto a pedestal array, the pedestal array having a top-side surface with pre-defined landings for the back-side surface of each of the singulated device die, the pedestal array having a pitch larger than that of the device die; and encapsulating each one of the singulated device die on the pedestal array, and the encapsulant enveloping the WLCSP devices and flowing under the angled recess of each WLCSP device.
The above summaries of the present disclosure are not intended to represent each disclosed embodiment, or every aspect, of the present invention. Other aspects and example embodiments are provided in the figures and the detailed description that follow.
The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which:
While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
DETAILED DESCRIPTIONThe disclosed embodiments have been found useful in preventing damage to the Wafer Level Chip-Scale Product (WLCSP) devices during their assembly. The process provides mechanical protection to the silicon device by encapsulating the device in a resilient material. Such a process may be integrated into the customary back-end assembly.
In an example embodiment, the user takes a wafer substrate having devices. The wafer undergoes electrical tests (e.g., E-sort) to sort out non-functioning devices; other processes may forego E-sort and cull out non-functioning devices after packaging. The tested wafers are mounted on an adhesive tape. The wafers are then sawed and separated out into individual device die. Using an appropriate molding apparatus, epoxy mold compound (EMC) is formed into a strip having pedestals. The dimensions (i.e., size, height, etc.) of a formed pedestal are smaller than that of the WLCSP device and are governed by the particular WLCSP product. Thus, the WLCSP device will have an overhanging edge on its underside. The overhang facilitates the flow of encapsulant around the product device and provides an anchor with enhanced strength to the protective encapsulant which seals five or six sides of the device. The individual device die are mounted on the pedestals using suitable die bond techniques. After the device die are mounted, the pedestal strip is over-molded; the molding compound may be the same of different than that used to form the pedestal strip. In some WLCSP devices, solder bumps may have been applied thereon and are protected using a foil-assisted apparatus. Having been sealed in encapsulant, the WLCSP product devices may be laser marked on the side opposite the side having the solder bumps. Saw tape is applied the marked side of the sealed devices; the product devices are then sawed and singulated.
In another example embodiment, the pedestal may be formed within the device die itself A wafer having device die is mounted on a grinding tape. With a first blade, a wafer having active device die has V-shaped saw marks defined on the backside of the wafer in the X and Y directions of the saw lanes surrounding the active devices. With a second blade, the active device die are sawed apart; the cut is continued from where the V-shape cut left off. A given device die has a pedestal profile on its vertical faces. A strip made of metal, packaging EMC or other suitable material, is made in such a way that its pitch is slightly larger than the size of the device die; a grid of pedestal locations are formed. The pedestal shape enhances the flow of encapsulant around the product and the pedestal shape (i.e., size, height, etc.) which is WLCSP-specific, provides enhanced mechanical anchoring of the encapsulant for either 5 or 6-side encapsulation. Singulated devices are mounted on the grid of pedestal locations and encapsulated. After encapsulation, the devices are sawed apart into separate device now-having a resilient protective material surrounding five or six sides.
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In another example embodiment, pedestals of metal may be placed onto a metal strip. In another example embodiment, the pedestals may be manufactured integral to a metal strip. In another example embodiment, the pedestals may be punched into a metal strip. Refer to
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Note that WL is flexible, based on different singulation saw blades used, thus a wide range is possible (as in Table 1), excluding manufacturing tolerances, the range is about 125 μm to about 250 μm.
In another example embodiment according to the present disclosure, the device die may be fabricated to have a pedestal defined integrally in its structure. Refer to
In another example embodiment, the “V” shaped profile may be accomplished with a photo-lithographic process. The front-side surface of the wafer substrate (containing the active devices) may be masked with a protective film. The back-side surface of the wafer substrate may be masked so as to leave exposed those areas corresponding to saw lanes of active devices. With a preferential etch, angled profiles, similar to those obtained with the sawing process discussed supra, may be achieved. The etching process may be a wet-etch, dry etch, or combination thereof.
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Having prepared the pedestal device die 615, having an angled profile with a recess 655, the user may select from a number of options in providing protection to the back-side surface of the die.
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Having provided protection on the five surfaces of the device die substantially minimizes the likelihood of assembly damage by the end-user building his subsystems.
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Numerous other embodiments of the invention will be apparent to persons skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.
Claims
1-12. (canceled)
13. A method for assembling wafer level chip scale processed (WLCSP) devices from a wafer substrate having a front-side surface upon which solder bumps are defined on active device die and an opposite back-side surface, the method comprising:
- applying a protection tape on the front-side surface;
- sawing with a “V-shaped” blade of a first kerf, on the back-side surface of the wafer substrate, in areas corresponding to saw lanes of the active device die, to a depth of about 50% of the wafer substrate thickness;
- continuing the sawing of the back-side surface with a blade of a second smaller kerf, so as to separate the active device die into singulated device die, wherein each of the singulated device die has an angled recessed profile with respect to the vertical faces of the device die;
- remounting the singulated device die on their front-side surfaces onto a sawing tape;
- die bonding the singulated device die onto a pedestal array, the pedestal array having a top-side surface with pre-defined landings for the back-side surface of each of the singulated device die, the pedestal array having a pitch larger than that of the device die; and
- encapsulating each one of the singulated device die on the pedestal array, and the encapsulant enveloping the WLCSP devices and flowing under the angled recess of each WLCSP device.
14. The method as recited in claim 13, further comprising, laser-marking an under-side surface of the pedestal array corresponding to device die locations.
15. The method as recited in claim 14, further comprising, placing the pedestal strip having encapsulated device die onto a sawing tape and sawing the encapsulated device into separate product devices.
16. The method as recited in claim 13, wherein the angled recessed profile is defined by:
- masking the front-side surface of the wafer substrate with a protective film;
- preferentially etching the back-side surface of the wafer substrate in areas corresponding to the saw lanes of the active devices, to about 50% of substrate thickness, so as to create sloped etch profile; and
- at the etched areas of the back-side surface of the wafer substrate, sawing with the blade of the second smaller kerf, so as to separate the active device die into singulated device die, wherein each of the singulated device die has an angled recess defined by the sloped etch profile with respect to the vertical faces of the device die.
17. The method as recited in claim 13, wherein the pedestal array is selected from one of the following: metal, plastic, a layered composite of plastic on metal.
Type: Application
Filed: Feb 19, 2015
Publication Date: Jun 11, 2015
Inventors: Leonardus Antonius Elisabeth VAN GEMERT (Nijmegen), Tonny KAMPHUIS (Lent), Hartmut BUENNING (Norderstedt), Christian ZENZ (Graz)
Application Number: 14/626,832