Patent Publication Number: US-2022221332-A1

Title: Optical system and method of manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/405,838 filed May 7, 2019, now U.S. Pat. No. 11,287,312, which application claims the benefit of and priority to U.S. Provisional Application No. 62/669,320, filed May 9, 2018, the contents of all such applications being incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to an optical system, and more particularly to an optical system including a light detector and a block structure. 
     2. Description of the Related Art 
     In an optical system (e.g., light scanning sensor, distance finding sensor, background-light sensing system), light emitters (e.g., vertical-cavity surface-emitting LASER (VCSEL) or light emitting diodes (LED)) and/or light detectors are used. In some optical systems, an encapsulant may be implemented to protect the light emitters or the light detectors. However, some of the light emitted by the light emitter may be reflected (e.g., interface reflection or total internal reflection) at a boundary between the encapsulant and air outside the encapsulant, and the reflected light may be received by the light detector to cause an unacceptable cross-talk issue and reduce the signal-noise ratio (SNR) of the optical system. 
     SUMMARY 
     In accordance with an aspect of the present disclosure, an optical system includes a carrier, a light emitter, a light receiver, a block structure and an encapsulant. The light emitter is disposed on the carrier. The light receiver is disposed on the carrier and physically spaced apart from the light emitter. The light receiver has a light detecting area. The block structure is disposed on the carrier. The encapsulant is disposed on the carrier and covers the light emitter, the light receiver and the block structure. The encapsulant has a recess over the block structure. 
     In accordance another aspect of the present disclosure, an optical system includes a carrier, a light emitter, a light receiver, a block structure and an encapsulant. The light emitter is disposed on the carrier. The light receiver is disposed on the carrier and physically spaced apart from the light emitter. The light receiver has a light detecting area on a top surface of the light receiver. The encapsulant is disposed on the carrier and covers the light emitter and at least a portion of the block structure. The block structure is disposed between the light emitter and the light receiver. The block structure has a curved surface. The encapsulant has a recess over the block structure. A distance between a bottom surface of the recess and the carrier is less than a distance between the light detecting area of the light receiver and the carrier. 
     In accordance another aspect of the present disclosure, a method of manufacturing an optical system includes (a) providing a carrier; (b) disposing a light emitter on the carrier; (c) disposing a light receiver on the carrier, the light receiver physically spaced apart from the light emitter; (d) forming an encapsulant on the carrier to cover the light emitter and the light receiver; and (e) forming a recess on the encapsulant block structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a cross-sectional view of an optical system in accordance with some embodiments of the present disclosure; 
         FIG. 2A  illustrates a cross-sectional view of an optical system in accordance with some embodiments of the present disclosure; 
         FIG. 2B  illustrates a perspective view of an optical system in accordance with some embodiments of the present disclosure; 
         FIG. 3A  illustrates a cross-sectional view of an optical system in accordance with some embodiments of the present disclosure; 
         FIG. 3B  illustrates a cross-sectional view of an optical system in accordance with some embodiments of the present disclosure; 
         FIG. 3C  illustrates a cross-sectional view of an optical system in accordance with some embodiments of the present disclosure; 
         FIG. 3D  illustrates a cross-sectional view of an optical system in accordance with some embodiments of the present disclosure; 
         FIG. 3E  illustrates a cross-sectional view of an optical system in accordance with some embodiments of the present disclosure; 
         FIG. 4  illustrates a cross-sectional view of an optical system in accordance with some embodiments of the present disclosure; 
         FIG. 5A  and  FIG. 5B  illustrate a method for manufacturing an optical system in accordance with some embodiments of the present disclosure; 
         FIG. 6A ,  FIG. 6B  and  FIG. 6C  illustrate a method for manufacturing an optical system in accordance with some embodiments of the present disclosure; and 
         FIG. 7A ,  FIG. 7B ,  FIG. 7C  and  FIG. 7D  illustrate a method for manufacturing an optical system in accordance with some embodiments of the present disclosure. 
     
    
    
     Common reference numerals are used throughout the drawings and the detailed description to indicate the same or similar components. The present disclosure can be best understood from the following detailed description taken in conjunction with the accompanying drawings. 
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a cross-sectional view of an optical system  1 . The optical system  1  includes a substrate  10 , a light emitter  11 , a light detector  12  and a lid  13 . As shown in  FIG. 1 , the lid  13  has a wall structure disposed between the light emitter  11  and the light detector  12 . In some embodiments, the lid  13  includes an opaque material to prevent undesired light emitted by the light emitters from being directly transmitted to the light detector. However, since the thickness (e.g., the thickness d 1 , d 2  or d 3 ) of the lid  13  is relatively great (e.g., the lid  13  has a total thickness increase about 0.5 millimeter (mm) in the x-direction or y-direction and a thickness of about 0.4 mm in the z-direction), the use of the lid  13  would hinder the miniaturization of the optical system  1 . 
       FIG. 2A  illustrates a cross-sectional view of an optical system  2  in some embodiments of the present disclosure. The optical system  2  includes a carrier  20 , a light emitter  21 , a light receiver  22 , a block structure (e.g., dam)  23  and an encapsulant  24 . 
     The carrier  20  may include, for example, a printed circuit board, such as a paper-based copper foil laminate, a composite copper foil laminate, or a polymer-impregnated (p.p.) glass-fiber-based copper foil laminate. The carrier  20  may include an interconnection structure, such as a plurality of conductive traces, pads or through vias. In some embodiments, the carrier  20  includes a ceramic material or a metal plate. In some embodiments, the carrier  20  may include a substrate, such as an organic substrate or a leadframe. In some embodiments, the carrier  20  may include a two-layer substrate which includes a core layer and a conductive material and/or structure disposed on an upper surface and a bottom surface of the carrier. The conductive material and/or structure may include a plurality of traces, pads, or vias. 
     The light emitter  21  is disposed on the carrier  20 . The light emitter  21  may include an emitting die or other optical die. For example, the light emitter  21  may include a light-emitting diode (LED), a laser diode, or another device that may include one or more semiconductor layers. The semiconductor layers may include silicon, silicon carbide, gallium nitride, or any other semiconductor materials. The light emitter  21  can be connected to the carrier  20  by way of flip-chip or wire-bond techniques, for example. In some embodiments, the light emitter  21  includes an LED die bonded on the carrier  20  via a die bonding material. The LED die includes at least one wire-bonding pad. The LED die is electrically connected to the carrier  20  by a conductive wire, one end of which is bonded to the wire-bonding pad of the LED die and another end of which is bonded to a wire-bonding pad of the carrier  20 . The light emitter  21  has an active region (or light emitting area) facing away from the carrier  20 . 
     The light receiver  22  is disposed on the carrier  20  and is physically spaced apart from the light emitter  21 . In some embodiments, the light receiver  22  includes, for example, a PIN diode (a diode including a p-type semiconductor region, an intrinsic semiconductor region, and an n-type semiconductor region) or a photo-diode or a photo-transistor. In some embodiments, the light receiver  22  detects the light from light emitter  21  and also includes some different sensing area with filter structure for ambient light sensing (ALS). The light receiver  22  can be connected to the carrier  20 , for example, by way of flip-chip or wire-bond techniques (e.g., through bonding wires  23   w ). The light receiver  22  has an active region  22   d  (or light detecting area) facing away from the carrier  20 . In some embodiments, the light receiver  22  may include a controller, a processor, a memory, an application-specific integrated circuit (ASIC) and the like. 
     The block structure (e.g., dam)  23  is disposed on the carrier  20  and across a portion of the light receiver  22  where the light detecting area  22   d  is not located. For example, the block structure  23  is disposed across other circuits integrated within the light receiver  22 . In some embodiments, the block structure  23  may be disposed across a portion of bonding wires  23   w  connecting the light receiver  22  to the carrier  20  as shown in  FIG. 2B , which illustrates a perspective view of the optical system  2  in  FIG. 2A . In some embodiments, the block structure  23  may cover a portion of the sidewall of the light receiver  22 . In some embodiments, a ratio of a width of a bottom surface of the block structure  23  to a height of the block structure  23  is about 2:1. In some embodiments, the block structure  23  may have a curved structure  23   c  at or adjacent to a top side of the block structure  23 . 
     In some embodiments, the block structure  23  includes an opaque material or a light absorbing material to prevent the light emitted by the light emitter  21  from being directly transmitted to the light receiver  22 . For example, as shown in  FIG. 2A , the light L 1  detected by the light receiver  22  is reflected by a target object  25 , while the light L 2  reflected (e.g., interface reflection) at the boundary of the encapsulant  24  and air outside the encapsulant  24  is blocked by the block structure  23 . Therefore, the cross-talk issue between the light emitter  21  and the light receiver  22  can be eliminated or mitigated, which can increase the SNR of the optical system  2 . 
     In some embodiments, the power of the light reflected at the boundary of the encapsulant  24  and air outside the encapsulant  24  and received by the light receiver  22  in  FIG. 2A  or  FIG. 2B  is about 1% to 5% less than that in an optical system without the block structure. For example, the power of the light reflected at the boundary of the encapsulant  24  and air outside the encapsulant  24  and received by the light receiver  22  in  FIG. 2A  or  FIG. 2B  may be about 0.063 micro watt (μW) with the block structure  23  and may be about 1.68 μW without the block structure  23 . In addition, because no lid is included in the optical system  2  to avoid cross-talk between the light emitter  21  and the light receiver  22 , the area and the thickness of the optical system  2  in  FIG. 2A  or  FIG. 2B  can be reduced to achieve a compact package size. 
     The encapsulant  24  is disposed on the carrier  20  and covers the light emitter  21 , the light receiver  22  and at least a portion of the block structure  23 . In some embodiments, a portion (e.g., a top surface) of the block structure  23  is exposed from the encapsulant  24 . The top surface of the block structure  23  is substantially coplanar with a top surface of the encapsulant  24 . In other embodiments, the block structure  23  can be fully covered by the encapsulant  24 . In some embodiments, the encapsulant  24  includes light transparent materials. For example, the encapsulant  24  is a clear compound. For example, the encapsulant  24  includes an epoxy resin. 
       FIG. 3A  illustrates a cross-sectional view of an optical system  3 A in some embodiments of the present disclosure. The optical system  3 A is similar to the optical system  2  in  FIG. 2A  except that the block structure  23  in  FIG. 3A  is not disposed across the light receiver  22 . For example, the block structure  23  is disposed between the light emitter  21  and the light receiver  22  and spaced apart from the light emitter  21  or the light receiver  22 . 
       FIG. 3B  illustrates a cross-sectional view of an optical system  3 B in some embodiments of the present disclosure. The optical system  3 A is similar to the optical system  3 A in  FIG. 3A , and the differences therebetween are described below. 
     As shown in  FIG. 3B , the encapsulant  24  has a recess  24   r . The recess is disposed between the light emitter  21  and the light receiver  22 . The recess  24   r  is disposed over the block structure  23 . In some embodiments, the recess  24   r  exposes the block structure  23 . In other embodiments, a lower side (e.g., a bottom surface or a bottom side) of the recess  24   r  is spaced apart from the block structure  23 . In some embodiments, the lower side of the recess  24   r  may be lower than, equal to or greater than the active region  22   d  of the light receiver  22  depending on different design specifications. 
     In some embodiments, the light receiver  22  is electrically connected to the carrier  20  through the bonding wires  23 . Due to the space (e.g., wireloop) specified for the bonding wires  23 , a thickness of the encapsulant  24  has a minimum limitation. For example, there should be a gap between the top surface of the encapsulant  24  and the light receiver  22  for accommodating the bonding wires  23 . In addition, as mentioned above, a ratio of the width of the bottom surface of the block structure  23  to the height of the block structure  23  should follow a rule (e.g.,  2 : 1 ), and thus if the height of the block structure  23  is designed to be the same as the thickness of the encapsulant  24 , the width of the block structure  23  would be relatively large, which will increase the area (increase package size) occupied by the block structure  23 . However, if the height of the block structure  23  is designed to be less than the thickness of the encapsulant  24  (e.g., a gap exists between the top surface of the encapsulant  24  and the top surface of the block structure  23 ), the light emitted from the light emitter  21  may directly enter the light receiver  22 , which would cause an unacceptable cross-talk issue and reduce the SNR. 
     In accordance with the embodiments as shown in  FIG. 3B , the recess  24   r  is formed over the block structure  23 , the light (e.g., L 33 ) emitted by the light emitter  21  may be refracted twice by the recess  24   r , in which one refraction occurs when the light emitted from the encapsulant  24  to the outside of the encapsulant  24 , and the other refraction occurs when the light emitted from the outside of the encapsulant  24  to the encapsulant  24 . Thus, the power of the light emitted by the light emitter  21  and directly entering the active region  22   d  of the light receiver  22  can be reduced. For example, the power of the light emitted by the light emitter  21  and directly entering the active region  22   d  of the light receiver  22  as shown in the structure of  FIG. 3B  may be 80% less than that of the structure without the recess. Therefore, by forming the recess  24   r  over the block structure  23 , the power of the light emitted by the light emitter  21  and directly entering the active region  22   d  of the light receiver  22  can be reduced without increasing the height of the block structure  23 . In addition, the block structure  23  includes an opaque material or a light absorbing material to prevent the light emitted by the light emitter  21  from being directly transmitted to the light receiver  22  (e.g., through the path L 34 ). 
       FIG. 3C  illustrates a cross-sectional view of an optical system  3 C in some embodiments of the present disclosure. The optical system  3 C is similar to the optical system  3 B in  FIG. 3B , except that the shape of the recess  24   r  in  FIG. 3C  is different from that of the recess  24   r  in  FIG. 3B . In some embodiments, the shape of the recess  24   r  can be designed depending on different design specifications. In some embodiments, a bottom surface of the recess  24   r  is spaced apart from the block structure  23 . For example, there is a gap between the recess  24   r  and the block structure  23 . 
       FIG. 3D  illustrates a cross-sectional view of an optical system  3 D in some embodiments of the present disclosure. The optical system  3 D in  FIG. 3D  is similar to the optical system  3 A in  FIG. 3A  except that the encapsulant  24  of the optical system  3 D in  FIG. 3D  has a recess  24   r  to expose a top surface of the block structure  23 . For example, a top surface of the encapsulant  24  is not coplanar with the top surface of the block structure  23 . In some embodiments, a hardness of the block structure  23  in  FIG. 3D  is greater than a hardness of the block structure  23  in  FIG. 2A  or  FIG. 3A . In some embodiments, a bottom surface of the recess  24   r  is substantially coplanar with a top surface of the block structure  23 . For example, the top surface of the block structure  23  is exposed from the recess  24   r . In some embodiments, a width of the recess  24   r  may be equal to or greater than a width of the block structure  23 . 
     Compared with the optical system  3 C in  FIG. 3C , the top surface of the block structure  23  in  FIG. 3D  is exposed from the recess, which may prevent the light emitted by the light emitter  21  from being directly transmitted to the light receiver  22 . For example, as shown in  FIG. 3D , the light L 31  reflected (e.g., interface reflection) at the boundary of the encapsulant  24  and air outside the encapsulant  24  is blocked by the block structure  23 . Therefore, the cross-talk issue between the light emitter  21  and the light receiver  22  can be eliminated or mitigated, which can increase the SNR of the optical system  3 D. 
       FIG. 3E  illustrates a cross-sectional view of an optical system  3 E in some embodiments of the present disclosure. The optical system  3 E in  FIG. 3E  is similar to the optical system  3 D in  FIG. 3D  and the differences therebetween are described below. 
     In some embodiments, the width of the recess  24   r  in  FIG. 3E  is less than the width of the block structure  23 . As shown in  FIG. 3E , the block structure  23  may have a cutting surface  24   r   1  that is exposed from the encapsulant  24 . The cutting surface  24   r   1  of the block structure  23  is recessed from the other portion of the block structure  23  surrounding the cutting surface  24   r   1 . In some embodiments, the recess  24   r  may be defined by the cutting surface  24   r   1  and at least a portion of the block structure  23 . The example, at least a portion of a sidewall of the recess  24   r  may be defined by a portion the block structure  23 . In some embodiments, the portion of the block may at least partially surround the cutting surface  24   r   1  and exposed from the encapsulant  24 . 
       FIG. 4  illustrates a cross-sectional view of an optical system  4  in some embodiments of the present disclosure. The optical system  4  in  FIG. 4  is similar to the optical system  2  in  FIG. 2A  except that the encapsulant  24  of the optical system  4  in  FIG. 4A  has a recess  24   r  to expose a top surface of the block structure  43 . For example, a top surface of the encapsulant  24  is not coplanar with the top surface of the block structure  43 . 
     As shown in  FIG. 4 , the light L 41  reflected (e.g., interface reflection) at the boundary of the encapsulant  24  and air outside the encapsulant  24  is blocked by the block structure  23 . Therefore, the cross-talk issue between the light emitter  21  and the light receiver  22  can be eliminated or mitigated, which can increase the SNR of the optical system  4 . In some embodiments, the power of the light reflected at the boundary of the encapsulant  24  and air outside the encapsulant  24  and received by the light receiver  22  may be about 0.028 μW. 
       FIG. 5A  and  FIG. 5B  illustrate a method of manufacturing an optical system in accordance with some embodiments of the present disclosure. In some embodiments, the method in  FIG. 5A  and  FIG. 5B  are used to manufacture the optical system  2  in  FIG. 2A . 
     Referring to  FIG. 5A , a carrier  20  is provided. A light emitter  21  and a light receiver  22  are disposed on the carrier  20  and physically spaced apart from each other. A block structure  23  is formed on the carrier  20  and across a portion of the light receiver  22  where the light detecting area  22   d  is not located. In some embodiments, the block structure  23  can be formed by dispensing opaque materials on the carrier  20  and the portion of the light receiver  22  where the light detecting area  22   d  is not located. In some embodiments, the block structure  23  includes silicon, epoxy or any other suitable materials (e.g., opaque materials or light absorbing materials). In some embodiments, the block structure  23  is relatively soft or flexible. For example, the block structure  23  can be formed of a material of Shore A50 or greater hardness. 
     A mold tool  50  with a film  50   f  then moves toward the carrier  20  to form the encapsulant  24  to cover the light emitter  21 , the light receiver  22  and the block structure  23  to form the optical system  2  as shown in  FIG. 5B . In some embodiments, the molding compound  24  is formed by compressive molding process. Since the support structure  23  is relatively soft or flexible, the block structure  23  would be compressed when pressing the mold tool  50  on the block structure  23 . Hence, there is no clearance between the top surface of the block structure  23  and the top surface of the encapsulant  24 . In other words, the top surface of the block structure  23  is substantially coplanar with the top surface of the encapsulant  24 . 
       FIG. 6A ,  FIG. 6B  and  FIG. 6C  illustrate a method of manufacturing an optical system from cross-sectional views in accordance with some embodiments of the present disclosure.  FIG. 7A ,  FIG. 7B ,  FIG. 7C  and  FIG. 7D  illustrate a method for manufacturing the optical system from perspective views in accordance with some embodiments of the present disclosure. In some embodiments, the method in  FIG. 6A ,  FIG. 6B  and  FIG. 6C  or  FIG. 7A ,  FIG. 7B ,  FIG. 7C  and  FIG. 7D  are used to manufacture the optical system  4  in  FIG. 4 . 
     Referring to  FIG. 6A  or  FIG. 7A , a carrier  20  is provided. A light emitter  21  and a light receiver  22  are disposed on the carrier  20  and physically spaced apart from each other. As shown in  FIG. 7A , the light receiver  22  is connected to the carrier  20  through bonding wires  22   w . A block structure  43 ′ is formed on the carrier  20  and across a portion of the light receiver  22  where the light detecting area  22   d  is not located. In some embodiments, the block structure  43 ′ is disposed across a portion of the bonding wires  22   w  as shown in  FIG. 7B . In some embodiments, the block structure  43 ′ may cover a portion of the sidewall of the light receiver  22 . In some embodiments, the block structure  43 ′ can be formed by dispensing opaque materials on the carrier  20  and the portion of the light receiver  22  where the light detecting area  22   d  is not located. In some embodiments, the block structure  43 ′ includes silicon, epoxy or any other suitable materials (e.g., opaque materials or light absorbing materials). In some embodiments, the block structure  43 ′ is relatively hard. For example, the block structure  43 ′ in  FIG. 6A  is harder than the block structure  23  in  FIG. 5A . For example, the block structure  43 ′ can be formed of a material of Shore C or greater hardness like Shore D90. 
     A mold tool  50  with a film  50   f  then moves toward the carrier  20  to form the encapsulant  24  to cover the light emitter  21 , the light receiver  22  and a portion of the block structure  43 ′ to form the optical system as shown in  FIG. 6B  or  FIG. 7C . In some embodiments, the encapsulant  24  is formed by compressive molding process. Since the block structure  43 ′ is relatively hard, the block structure  43 ′ would not be deformed when pressing the mold tool  50  on the block structure  43 ′. Therefore, as shown in  FIG. 6B , the block structure  43 ′ protrudes the top surface of the encapsulant  24 . The film  50   f  is formed of a soft material to provide a buffer for the block structure  43 ′ to avoid crack. 
     Referring to  FIG. 6C  or  FIG. 7D , a cutting operation (e.g., half cut) is carried out to remove a portion of the block structure  43 ′ and a portion of the encapsulant to form a recess  24   r . A top surface of the rest portion of the block structure  43  is exposed from the encapsulant  24 . For example, the top surface of the encapsulant  24  is higher than the top surface of the block structure  43 . For example, the top surface of the block structure  43  is recessed from the top surface of the encapsulant  24 . 
     As used herein, the terms “substantially,” “substantial,” “approximately,” and “about” are used to denote and account for small variations. For example, when used in conjunction with a numerical value, the terms can refer to a range of variation of less than or equal to ±10% of that numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. As another example, a thickness of a film or a layer being “substantially uniform” can refer to a standard deviation of less than or equal to ±10% of an average thickness of the film or the layer, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. The term “substantially coplanar” can refer to two surfaces within 50 μm of lying along a same plane, such as within 40 within 30 within 20 within 10 or within 1 μm of lying along the same plane. Two components can be deemed to be “substantially aligned” if, for example, the two components overlap or are within 200 within 150 within 100 within 50 within 40 within 30 within 20 within 10 or within 1 μm of overlapping. Two surfaces or components can be deemed to be “substantially perpendicular” if an angle therebetween is, for example, 90°±10°, such as ±5°, ±4°, ±3°, ±2°, ±1°, ±0.5°, ±0.1°, or ±0.05°. When used in conjunction with an event or circumstance, the terms “substantially,” “substantial,” “approximately,” and “about” can refer to instances in which the event or circumstance occurs precisely, as well as instances in which the event or circumstance occurs to a close approximation. 
     In the description of some embodiments, a component provided “on” another component can encompass cases where the former component is directly on (e.g., in physical contact with) the latter component, as well as cases where one or more intervening components are located between the former component and the latter component. 
     Additionally, amounts, ratios, and other numerical values are sometimes presented herein in a range format. It can be understood that such range formats are used for convenience and brevity, and should be understood flexibly to include not only numerical values explicitly specified as limits of a range, but also all individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly specified. 
     While the present disclosure has been described and illustrated with reference to specific embodiments thereof, these descriptions and illustrations do not limit the present disclosure. It can be clearly understood by those skilled in the art that various changes may be made, and equivalent elements may be substituted within the embodiments without departing from the true spirit and scope of the present disclosure as defined by the appended claims. The illustrations may not necessarily be drawn to scale. There may be distinctions between the artistic renditions in the present disclosure and the actual apparatus, due to variables in manufacturing processes and such. There may be other embodiments of the present disclosure which are not specifically illustrated. The specification and drawings are to be regarded as illustrative rather than restrictive. Modifications may be made to adapt a particular situation, material, composition of matter, method, or process to the objective, spirit and scope of the present disclosure. All such modifications are intended to be within the scope of the claims appended hereto. While the methods disclosed herein have been described with reference to particular operations performed in a particular order, it can be understood that these operations may be combined, sub-divided, or re-ordered to form an equivalent method without departing from the teachings of the present disclosure. Therefore, unless specifically indicated herein, the order and grouping of the operations are not limitations of the present disclosure.