Patent Application
20130087379
Embodiments of the present disclosure generally relate to bulk acoustic wave (BAW) and surface acoustic wave (SAW) devices, and more particularly to such devices having a clean and robust air cavity styled package.
SAW and BAW device manufacturers are incorporating wafer-level packaging (WLP) solutions to meet the size and cost reduction demands of the wireless communications market. For proper acoustic performance, SAW and BAW devices provide a clean air cavity over an acoustically active area of a substrate. Techniques currently exist to provide a clean air cavity through the use of different types of sacrificial layers. However, such techniques may be associated with degradation of electrical performance of the SAW and BAW devices through various process and/or testing operations to which the devices may be subjected.
For a fuller understanding of the invention, reference is made to the following detailed description, which, taken in connection with the accompanying drawings, illustrate various embodiments of the present invention, in which:
The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.
An exterior surface 24 of the enclosure 18 includes one or more sharp portion(s) 26, formed, for example, by surface portion 26a being in an angled position relative to adjacent surface portion 26b, such as sides forming corners, by way of example. The sharp portion(s) 26 may be any type of sharpness, and is not limited to sides coming together at a 90-degree angle, e.g., sharp portion(s) 26 may be formed by sides coming together at a 135-degree angle, a 90-degree angle, a 45-degree angle, or any angle. In addition, sharp portion(s) 26 need not be absolutely sharp, but only need be sufficiently sharp to benefit from the teachings of the present invention.
Developed photosensitive layer 30 encapsulates the enclosure 18. The developed photosensitive layer 30 may be secured to the exterior surface 24 of the enclosure 18 and may form a patterned shape 32 resulting from the developing of the developed photosensitive layer 30. As will be described later, the developed photosensitive layer 30 is reflowed prior to curing, such that the developed photosensitive layer 30 provides smooth portion(s) 31 on an outer surface 34. The smooth portion(s) 31 may be adjacent to sharp portion(s) 26 of the exterior surface 24 of the enclosure 18. In some embodiments, the outer surface 34 of the developed photosensitive layer 30 may be an agonic surface. Outer surface 34 smoothes out sharp portion(s) 26 of exterior surface 24 of the enclosure 18 such that the sharpness present in sharp portion 26 on exterior surface 24 of enclosure 18 is not present on the outer surface 34.
An inorganic layer 36 covers the outer surface 34 and thus takes on characteristics of the outer surface 34, thereby providing a desirable agonic and generally smooth outer surface 38. A top portion 40 of the inorganic layer 36 defined above a top wall 42 of the enclosure 18, and generally above the cavity 20, is dome shaped. The dome shape of the top portion 40 of the inorganic layer 36 may be the result of a similar dome shape of the underlying photosensitive layer 30. The dome shape of the photosensitive layer 30 may be a result of a reflow operation as discussed below.
Wafer level package 10 thus may have a domed top surface 46 that has a center portion 46C that is higher than side surface portions 46S, relative to the substrate 12 by a dome height 48 in one embodiment. This provides added strength for supporting subsequent processing of wafer level package 10, such as overmolding procedures. Enclosure 18, developed photosensitive layer 30 and inorganic layer 36 together form wafer level package 10 having a structural strength sufficient to withstand significant overmold pressures, e.g., overmold pressures up to 1000 psi.
In one embodiment, enclosure 18 is formed from a photo definable epoxy, such as, for example, a SU8 epoxy resin. Substrate 12, may be, for example, Si, GaAs, LiTaO3, LiNbO3 or glass. Inorganic layer 36 may be a rigid dielectric layer formed from a nitride material, such as, for example, silicon nitride or silicon oxi-nitride, thereby forming inorganic layer 36 as a moisture resistant layer. Developed photosensitive layer 30 may be formed from a positive resist photosensitive material, for example, AZ4330, AZ4620, AZ4999, bisbenzocyclobutene (BCB) or a polyimide material.
In one embodiment of the present invention, heat is applied to the developed photosensitive layer 30, permitting the material forming developed photosensitive layer 30 to reflow and form the outer surface 34 as, e.g., an agonic surface. As a result, the sharp portion(s) 26 of exterior surface 24 are covered by developed photosensitive layer 30 that now has smooth outer surface 34. As a result of the reflow baking operation, the outer surface 34 may take on a dome shape 35 above the cavity 18. The reflowed developed photosensitive layer 30 is then cured to form a hardened overcoat having the outer surface 34, resulting in the formative stage of the wafer level package 10 illustrated in
The reflowing of developed photosensitive layer 30 will smooth the sharp portion(s) to various degrees depending upon the temperatures applied, as illustrated with reference to
Developed photosensitive layer 30 may be applied through a spin coating process, a spray coating process, a dry film laminating process, or other processes. Prior to applying the developed photosensitive layer 30, enclosure 18 and exposed portions of substrate 12 may be cleaned to enhance dielectric adhesion of developed photosensitive layer 30 to enclosure 18 and exposed portions of the substrate 12.
Following the processing stage of
Inorganic layer 36 may be deposited by, for example, microelectronics techniques, such as plasma enhanced chemical vapor deposition (PECVD), PVD, a chemical solution deposition referred to as sol gel, and the like.
Now protected, the electronic device 16 may be capable of withstanding a variety of process and/or testing operations, such as, for example, mold transfer, and autoclave or Hast tests. Embodiments of the present invention may be compatible with, for example, chip and wire assembly processes and bumping processes. In addition, wafer level package 10 may be ready, for example, to be diced, taped, reeled and directly assembled on a laminate board.
While embodiments of the present disclosure are described with respect to acoustic wave filters, e.g., BAW and SAW filters, other embodiments may include other types of devices that benefit from the described clean and robust air-cavity packages. For example, packages of other embodiments may be used in microelectromechanical systems (MEMS), micro-fluidic MEMS, nanoelectromechanical systems (NEMS), etc.
Many modifications and other embodiments of the invention will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of the appended claims.
