阅读说明：本技术 一种2.5d封装结构及其制造方法 (2.5D packaging structure and manufacturing method thereof ) 是由 刘军 曹立强 于 2019-10-16 设计创作，主要内容包括：本发明公开了一种2.5D封装结构,包括：转接板；导电硅通孔,所述导电硅通孔设置在贯穿所述转接板的内部；转接板正面重新布局布线层,所述转接板正面重新布局布线层电连接所述导电硅通孔；第一芯片,所述第一芯片设置在所述转接板正面重新布局布线层的上方,并与所述转接板正面重新布局布线层电连接；第二芯片,所述第二芯片设置在所述转接板正面重新布局布线层的上方,并与所述转接板正面重新布局布线层电连接；底填胶层,所述底填胶设置在所述第一芯片和或所述第二芯片的底部与所述正面重新布局布线层之间；正面塑封层,所述正面塑封层包覆所述第一芯片和所述第二芯片；转接板背面金属层。(The invention discloses a 2.5D packaging structure, which comprises: an adapter plate; the conductive silicon through hole is arranged in the adapter plate in a penetrating manner; a wiring layer is rearranged on the front surface of the adapter plate, and the wiring layer is rearranged on the front surface of the adapter plate and electrically connected with the conductive silicon through hole; the first chip is arranged above the redistribution layer on the front surface of the adapter plate and is electrically connected with the redistribution layer on the front surface of the adapter plate; the second chip is arranged above the redistribution layer on the front surface of the adapter plate and is electrically connected with the redistribution layer on the front surface of the adapter plate; the underfill is arranged between the bottom of the first chip and/or the second chip and the front-side re-layout wiring layer; the front surface plastic package layer wraps the first chip and the second chip; and a metal layer on the back of the adapter plate.)

1. A 2.5D package structure, comprising:

an adapter plate;

the conductive silicon through hole is arranged in the adapter plate in a penetrating manner;

a wiring layer is rearranged on the front surface of the adapter plate, and the wiring layer is rearranged on the front surface of the adapter plate and electrically connected with the conductive silicon through hole;

the first chip is arranged above the redistribution layer on the front surface of the adapter plate and is electrically connected with the redistribution layer on the front surface of the adapter plate;

the second chip is arranged above the redistribution layer on the front surface of the adapter plate and is electrically connected with the redistribution layer on the front surface of the adapter plate;

the underfill is arranged between the bottom of the first chip and/or the second chip and the front-side re-layout wiring layer;

the front surface plastic package layer wraps the first chip and the second chip;

the back metal layer of the adapter plate is electrically connected with the conductive silicon through hole, so that the wiring layer, the first chip and the second chip are electrically connected with the front surface of the adapter plate in a re-layout mode;

the external solder balls are arranged on the external bonding pads of the metal layer on the back surface of the adapter plate; and

and the back surface plastic package layer coats the back surface of the adapter plate except the external solder balls.

2. The 2.5D package structure of claim 1, further comprising a third chip disposed above and electrically connected to the interposer front-side redistribution routing layer.

3. The 2.5D package structure of claim 1, wherein the interposer is a silicon interposer with a thickness of 80 to 130 microns.

4. The 2.5D package structure of claim 1, wherein the redistribution layer on the front side of the interposer is a single-layer or multi-layer conductive metal layer and has a dielectric layer disposed between a metal layer on the same layer and a metal layer on an adjacent layer, wherein the last metal layer further includes M chip pads, and M ≧ 2.

5. The 2.5D package structure of claim 4, wherein the first chip and or the second chip are disposed on the chip pad by flip chip bonding.

6. The 2.5D package structure of claim 1, wherein the front molding compound covers the first chip and the second chip and also covers a sidewall of the interposer.

7. The 2.5D package structure of claim 6, wherein the back side molding compound and the front side molding compound together form an encapsulation protection for all package structures except the external solder balls.

8. A manufacturing method of a 2.5D packaging structure comprises the following steps:

forming a conductive silicon through hole, a re-layout wiring layer, a dielectric layer and a cutting way on a substrate;

chip mounting is carried out, and an underfill layer is formed at the bottom of the chip;

forming a semi-cutting groove in the substrate below the cutting channel;

the front side plastic package is used for completing wafer reconstruction of the chip, and the front side plastic package layer is used for filling the semi-cutting groove;

thinning the back of the substrate to realize the back metal leakage of the conductive silicon through hole and the back leakage of the front plastic package layer in the semi-cutting groove;

forming a back metal layer and an external solder ball on the back of the substrate;

forming a back plastic packaging layer; and

and cutting to form single package structures.

9. The method of claim 8, wherein after the singulation, the front molding compound covers the top surface and the side surfaces of the package structure, and the back molding compound covers the bottom surface of the package structure except for the solder balls and is connected to the front molding compound to realize a six-sided package structure.

Technical Field

The invention relates to the technical field of semiconductor packaging, in particular to a 2.5D packaging structure and a manufacturing method thereof.

Background

CoWOS (Chip-on-Wafer-on-Substrate) and InFO (integrated Fan out) are 2.5D packaging technologies that are bench-integrated electro-mechanical push-out, also known as Wafer level packaging. The 2.5D package technology for power build-up packages chips onto a silicon interposer and interconnects them using high density routing on the silicon interposer. CoWOS is mainly aimed at high-end markets, and the number, density and packaging size of interconnection lines are large. Aiming at the cost performance market, the InFO has smaller packaging size and fewer connecting lines.

The conventional CoWOS process for accumulating electricity mainly comprises two schemes, wherein one scheme is that the silicon adapter plate is manufactured firstly, and then the chip is subjected to processes such as chip mounting, packaging (plastic packaging) and the like, and multiple bonding and bonding disassembling processes are required in the scheme, so that the bonding adhesive residue is increased, and the yield is reduced; in another scheme, the front process of the silicon adapter plate is firstly completed, then the processes of chip mounting, packaging (plastic packaging) and the like are carried out, then the adapter plate is thinned, and the back process of the adapter plate is carried out.

Aiming at the problems of bonding glue residue, wafer warpage and the like in the conventional CoWOS process, the invention provides a 2.5D packaging structure and a manufacturing method thereof, which at least partially overcome the problems.

Disclosure of Invention

According to an embodiment of the present invention, a 2.5D package structure is provided, which includes:

an adapter plate;

the conductive silicon through hole is arranged in the adapter plate in a penetrating manner;

a wiring layer is rearranged on the front surface of the adapter plate, and the wiring layer is rearranged on the front surface of the adapter plate and electrically connected with the conductive silicon through hole;

the first chip is arranged above the redistribution layer on the front surface of the adapter plate and is electrically connected with the redistribution layer on the front surface of the adapter plate;

the second chip is arranged above the redistribution layer on the front surface of the adapter plate and is electrically connected with the redistribution layer on the front surface of the adapter plate;

the underfill is arranged between the bottom of the first chip and/or the second chip and the front-side re-layout wiring layer;

the front surface plastic package layer wraps the first chip and the second chip;

the back metal layer of the adapter plate is electrically connected with the conductive silicon through hole, so that the wiring layer, the first chip and the second chip are electrically connected with the front surface of the adapter plate in a re-layout mode;

the external solder balls are arranged on the external bonding pads of the metal layer on the back surface of the adapter plate; and

and the back surface plastic package layer coats the back surface of the adapter plate except the external solder balls.

In an embodiment of the present invention, the 2.5D package structure further includes a third chip, and the third chip is disposed above the interposer front-side redistribution wiring layer and electrically connected to the interposer front-side redistribution wiring layer.

In one embodiment of the present invention, the interposer is a silicon interposer with a thickness of 80 to 130 microns.

In one embodiment of the invention, the redistribution layer on the front surface of the interposer is a single-layer or multi-layer conductive metal layer and has a dielectric layer arranged between a metal layer on the same layer and a metal layer adjacent to the metal layer, wherein the last metal layer further comprises M chip bonding pads, and M is greater than or equal to 2.

In one embodiment of the present invention, the first chip and/or the second chip are disposed on the chip pad by flip chip bonding.

In an embodiment of the invention, the front surface molding compound covers the side walls of the interposer while covering the first chip and the second chip.

In an embodiment of the invention, the back surface molding compound and the front surface molding compound together form an encapsulation protection for all package structures except the external solder balls.

In another embodiment of the present invention, a method for manufacturing a 2.5D package structure is provided, including:

forming a conductive silicon through hole, a re-layout wiring layer, a dielectric layer and a cutting way on a substrate;

chip mounting is carried out, and an underfill layer is formed at the bottom of the chip;

forming a semi-cutting groove in the substrate below the cutting channel;

the front side plastic package is used for completing wafer reconstruction of the chip, and the front side plastic package layer is used for filling the semi-cutting groove;

thinning the back of the substrate to realize the back metal leakage of the conductive silicon through hole and the back leakage of the front plastic package layer in the semi-cutting groove;

forming a back metal layer and an external solder ball on the back of the substrate;

forming a back plastic packaging layer; and

and cutting to form single package structures.

In another embodiment of the present invention, after the division, the front surface molding compound covers the top surface and the side surfaces of the package structure, and the back surface molding compound covers the bottom surface of the package structure except the solder balls, and is connected to the front surface molding compound, so as to realize a six-sided package structure.

The invention provides a 2.5D packaging structure and a manufacturing method thereof.A front surface of an adapter plate is sequentially provided with an interconnection layer and a chip, a back surface is provided with an external solder ball, and six surfaces of the packaging structure are coated by plastic packaging layers on the front surface and the back surface. The manufacturing method of the structure comprises the following steps: completing the front process of the silicon adapter plate on the silicon chip to form a welding pad or a salient point for the flip chip; forming a groove by using a wafer cutting process half-cut or wet etching mode, wherein the depth of the groove is larger than the thickness of the final adapter plate; then finishing the flip chip and whole wafer plastic package process; thinning the plastic package material, and then performing back thinning of the adapter plate and a head exposing process of the TSV copper column to complete the back process of the adapter plate; then, the whole wafer is taken as a whole to carry out the plastic packaging process of bump protection, and the adapter plate is completely embedded into the plastic packaging material; and finally, cutting is finished, and the cutting width is required to be smaller than that of the preset groove, so that the plastic sealing glue can form protection on the side wall. The final single product obtained based on the 2.5D packaging structure and the manufacturing method thereof provided by the invention is completely wrapped by the plastic sealing adhesive except for the exposed solder ball salient points, so that good mechanical strength is formed; the grooves which are wider than the common cutting lines are added in the manufacturing process, and the grooves are filled by the plastic packaging material, so that the stress of the plastic packaging material which is not matched with the CTE of silicon can be effectively released; after the TSV copper columns are exposed, the plastic packaging material in the grooves is also exposed, and warping balance of the whole wafer is facilitated.

Drawings

To further clarify the above and other advantages and features of embodiments of the present invention, a more particular description of embodiments of the invention will be rendered by reference to the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. In the drawings, the same or corresponding parts will be denoted by the same or similar reference numerals for clarity.

Fig. 1 shows a cross-sectional schematic view of a 2.5D package structure 100 according to an embodiment of the invention.

Fig. 2A to 2F are cross-sectional projection views illustrating a process of forming the 2.5D package structure 100 according to an embodiment of the invention.

Fig. 3 illustrates a flow diagram 300 for forming such a 2.5D package structure 100 according to an embodiment of the present invention.

Detailed Description

In the following description, the invention is described with reference to various embodiments. One skilled in the relevant art will recognize, however, that the embodiments may be practiced without one or more of the specific details, or with other alternative and/or additional methods, materials, or components. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of embodiments of the invention. Similarly, for purposes of explanation, specific numbers, materials and configurations are set forth in order to provide a thorough understanding of the embodiments of the invention. However, the invention may be practiced without specific details. Further, it should be understood that the embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale.

Reference in the specification to "one embodiment" or "the embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.

It should be noted that, in the embodiments of the present invention, the process steps are described in a specific order, however, this is only for convenience of distinguishing the steps, and the order of the steps is not limited, and in different embodiments of the present invention, the order of the steps may be adjusted according to the adjustment of the process.

The invention provides a 2.5D packaging structure and a manufacturing method thereof.A front surface of an adapter plate is sequentially provided with an interconnection layer and a chip, a back surface is provided with an external solder ball, and six surfaces of the packaging structure are coated by plastic packaging layers on the front surface and the back surface. The manufacturing method of the structure comprises the following steps: completing the front process of the silicon adapter plate on the silicon chip to form a welding pad or a salient point for the flip chip; forming a groove by using a wafer cutting process half-cut or wet etching mode, wherein the depth of the groove is larger than the thickness of the final adapter plate; then finishing the flip chip and whole wafer plastic package process; thinning the plastic package material, and then performing back thinning of the adapter plate and a head exposing process of the TSV copper column to complete the back process of the adapter plate; then, the whole wafer is taken as a whole to carry out the plastic packaging process of bump protection, and the adapter plate is completely embedded into the plastic packaging material; and finally, cutting is finished, and the cutting width is required to be smaller than that of the preset groove, so that the plastic sealing glue can form protection on the side wall. The final single product obtained based on the 2.5D packaging structure and the manufacturing method thereof provided by the invention is completely wrapped by the plastic sealing adhesive except for the exposed solder ball salient points, so that good mechanical strength is formed; the grooves which are wider than the common cutting lines are added in the manufacturing process, and the grooves are filled by the plastic packaging material, so that the stress of the plastic packaging material which is not matched with the CTE of silicon can be effectively released; after the TSV copper columns are exposed, the plastic packaging material in the grooves is also exposed, and warping balance of the whole wafer is facilitated.

A 2.5D package structure according to an embodiment of the present invention is described in detail below with reference to fig. 1. Fig. 1 shows a cross-sectional schematic view of a 2.5D package structure 100 according to an embodiment of the invention. As shown in fig. 1, the 2.5D package structure 100 further includes an interposer 110, a conductive Through Silicon Via (TSV)120, an interposer front redistribution layer 130, a first chip 140-1, a second chip 140-2, an underfill layer 150, a front molding layer 160, an interposer back metal layer 170, external solder balls 180, and a back molding layer 190.

Interposer 110 is typically a silicon interposer. In one embodiment of the present invention, the interposer 110 has a thickness of about 100 microns. In yet another embodiment of the present invention, the interposer 110 may also be an interposer of glass or other material.

A conductive Through Silicon Via (TSV)120 is disposed inside the interposer 110, penetrating the interposer 110. In one embodiment of the present invention, the depth of the conductive Through Silicon Via (TSV)120 is about 100 μm, the main conductive material of the conductive Through Silicon Via (TSV)120 is copper metal, and a barrier layer (not shown) is disposed adjacent to the interposer 110 to prevent the copper metal from diffusing into the interposer.

The interposer front-side redistribution wiring layer 130 is disposed on the front side of the interposer 110 and electrically connected to the conductive Through Silicon Vias (TSVs) 120, and the metal on the topmost layer of the interposer front-side redistribution wiring layer 130 has a chip pad (not shown). In one embodiment of the present invention, the interposer front-side redistribution layer 130 may have a single layer or multiple layers of conductive metal layers, and the conductive metal material may be selected from copper, aluminum, tungsten, and the like. The same layer of conductive metal of the wiring layer 130 is rearranged on the front surface of the interposer, or a dielectric layer 131 is further included between multiple layers of conductive metal layers, which plays a role in electrical insulation and mechanical support.

The first chip 140-1 and the second chip 140-2 are flip-chip bonded to the chip pads of the redistribution layer 130 on the front side of the interposer. In yet another embodiment of the present invention, the interconnection of the first chip 140-1 or the second chip 140-2 and the interposer front-side re-layout wiring layer 130 may be achieved by mounting the patch and then bonding wires. The first chip 140-1 and the second chip 140-2 may be heterogeneous chips, or chips with similar or identical functions.

The underfill layer 150 is disposed on the bottom of the first chip 140-1 and the second chip 140-2, and plays a role in protecting the flip chip bonding structure.

The front molding compound layer 160 covers the entire first chip 140-1, the entire second chip 140-2, and the exposed front and side surfaces of the interposer, wherein the side surfaces include 4 front, back, left, and right surfaces. Therefore, the front molding layer 160 forms an integral covering of the interposer 110 and the front package structure thereof.

The interposer backside metal layer 170 is disposed on the backside of the interposer 110 and electrically connected to the conductive Through Silicon Vias (TSVs) 120. Similar to the interposer front-side redistribution routing layer 130, there may be a single or multiple conductive layers, with the outermost layer having external bond pads (not shown).

The external solder balls 180 are disposed at the external pads of the interposer backside metal layer 170, and may be formed by electroplating, reflow, or ball-mounting. In one embodiment of the present invention, the external solder ball 180 may also be a conductive Copper pillar (Copper pillar).

The back molding layer 190 is disposed on the interposer back metal layer 170 except the solder balls, and forms a protection for the back surface of the interposer 110, and forms an encapsulation protection for the whole package structure (except the solder balls) together with the front molding layer 160.

A process of forming such a 2.5D package structure 100 is described in detail below with reference to fig. 2A to 2F and fig. 3. Fig. 2A-2F are cross-sectional projection views illustrating a process of forming such a 2.5D package structure 100 according to an embodiment of the present invention; fig. 3 illustrates a flow diagram 300 for forming such a 2.5D package structure 100 according to an embodiment of the present invention.

First, in step 301, as shown in fig. 2A, a conductive through silicon via 211, a re-layout wiring layer 212, a dielectric layer 213, and a scribe line 214 are formed on a substrate 210. In an embodiment of the present invention, a TSV via is completed on a silicon substrate, the TSV via depth is generally about 100 μm, but not limited to this depth, and then conductive filling of the TSV is completed using a conductive material such as copper, so as to form a final conductive silicon via 211; and then, the manufacturing of the wiring layer 212 is rearranged on the front surface of the interposer, and the scribe line 214 is reserved, wherein the width of the scribe line 214 is about 20 micrometers compared with that of the conventional scribe line, and the width of the scribe line is finally required to be more than 100 micrometers. In another embodiment of the present invention, the scribe line 214 is formed by additive method and patterning to form the redistribution layer 212 and the dielectric layer 213. In yet another embodiment of the present invention, the scribe line 214 is formed by etching, mechanical cutting, laser cutting, etc. the formed redistribution layer 212 and the dielectric layer 213 are formed.

Next, in step 302, as shown in fig. 2B, the chips 220 and 230 are mounted, an underfill 240 is formed on the bottoms of the chips 220 and 230, and a half-cut 250 is formed in the substrate 210 under the scribe line 214. In one embodiment of the present invention, the chips 220, 230 are flip-chip bonded by BGA solder balls (e.g., chip solder balls, copper pillars, etc.) located on the chips at chip pad locations (not shown) of the re-layout wiring layer 212. In yet another embodiment of the present invention, the chip 220 and/or the chip 230 may be disposed on the redistribution routing layer 212 by a face-up patch, and then the chip 220 and/or the chip 230 is electrically connected to the lower redistribution routing layer 212 by a wire bonding process. The half-cut grooves 250 are formed in a manner that the substrate 210 below the scribe lines 214 is cut by a dicing blade; in another embodiment of the present invention, the half-cut 250 is formed by etching (e.g., dry etching by reactive ions or wet etching by a solution such as potassium hydroxide) the substrate 210 under the scribe line 214.

Then, in step 303, as shown in fig. 2C, a front molding layer 260 is formed to complete the wafer reconfiguration of the chips 220 and 230. In one embodiment of the present invention, the wafer of chips 220, 230 is fully encapsulated, and the molding layer 260 covers the chips 220, 230 and the entire front surface of the substrate 210 and effectively fills the half-cuts 250. In order to achieve better filling effect, in another embodiment of the present invention, a vacuum plastic package technique is adopted to obtain better and more sufficient access of the plastic package layer 260 to the inside of the half-cutting grooves 250. In another embodiment of the present invention, the plastic packaging surface of the plastic packaged reconstituted wafer is thinned, the thinning is mainly to obtain a smoother reconstituted wafer, and the thinner plastic packaging is more favorable for overcoming the warpage of the whole product.

Next, in step 304, as shown in fig. 2D, the back surface of the substrate 210 is thinned to realize metal leakage from the back surface of the conductive through-silicon via 211 and leakage from the back surface of the molding layer 260 in the half-cut groove 250, so that the silicon substrate 210 in the whole reconstituted wafer is divided into many small modules, and the molding layer 260 (usually resin) between the modules can effectively suppress the warpage of the reconstituted wafer.

Then, in step 305, as shown in fig. 2E, a backside metal layer 270 and external solder balls 280 are formed on the backside of the substrate 210, and a backside molding layer 290 is formed. In an embodiment of the present invention, after the back surface of the substrate 210 is thinned and the metal on the back surface of the conductive through-silicon-via 211 and the plastic package layer 260 in the half-cutting groove 250 are exposed, a back metal layer 270 is fabricated, the back metal layer 270 is similar to the re-layout wiring layer 212 on the front surface of the substrate 210 and can be formed by patterned electroplating, and the back metal layer 270 is electrically connected to the conductive through-silicon-via 211, so as to achieve electrical interconnection with the re-layout wiring layer 212 and the chips 220 and 230 in the package structure; the external solder balls 280 are formed on the external pads (not shown) of the back metal layer 270 by plating, ball-planting, etc. to implement electrical and/or signal connection between the package structure and an external motherboard or system. In another embodiment of the present invention, after the external solder balls 280 are manufactured, a plastic package process is performed again to form a back plastic package layer 290, the back plastic package layer 290 covers the back surface of the substrate 210 where the external solder balls 280 are located, only the external solder balls leak out, and the back plastic package layer 290 is connected to the plastic package layer 260 in the half-cut groove 250 to form an integral package of the package structure. The main purpose is as follows: on one hand, the external solder balls 280 are protected (the thickness of the general plastic package is about half of the height of the external solder balls, so that the protection effect can be effectively achieved), and on the other hand, the back plastic package layer 290 is formed, so that the warpage of the whole product can be effectively reduced, and the whole reconstructed wafer tends to zero warpage. In another embodiment of the present invention, the external solder balls 280 may also be conductive copper pillars.

Finally, in step 306, as shown in fig. 2F, the individual package structures 100 are formed by singulation. The specific segmentation is that through the reconsitution wafer after accomplishing back plastic envelope, use the cutting knife to cut the cutting street, the width of cutting knife generally needs to be less than about 20 to 30 microns of the width of initial cutting street 214, finally realizes that single packaging structure's silicon keysets 210's lateral wall, top and bottom all are protected by plastic envelope resin, has increased the structural strength of product, and the keysets front back all has resin in addition, and its warpage performance will be better under high temperature processing procedure.

Based on the 2.5D packaging structure and the manufacturing method thereof provided by the invention, the front surface of the adapter plate is sequentially provided with the interconnection layer and the chip, the back surface of the adapter plate is provided with the external solder balls, and six surfaces of the packaging structure are coated by the plastic packaging layers on the front surface and the back surface. The manufacturing method of the structure comprises the following steps: completing the front process of the silicon adapter plate on the silicon chip to form a welding pad or a salient point for the flip chip; forming a groove by using a wafer cutting process half-cut or wet etching mode, wherein the depth of the groove is larger than the thickness of the final adapter plate; then finishing the flip chip and whole wafer plastic package process; thinning the plastic package material, and then performing back thinning of the adapter plate and a head exposing process of the TSV copper column to complete the back process of the adapter plate; then, the whole wafer is taken as a whole to carry out the plastic packaging process of bump protection, and the adapter plate is completely embedded into the plastic packaging material; and finally, cutting is finished, and the cutting width is required to be smaller than that of the preset groove, so that the plastic sealing glue can form protection on the side wall. The final single product obtained based on the 2.5D packaging structure and the manufacturing method thereof provided by the invention is completely wrapped by the plastic sealing adhesive except for the exposed solder ball salient points, so that good mechanical strength is formed; the grooves which are wider than the common cutting lines are added in the manufacturing process, and the grooves are filled by the plastic packaging material, so that the stress of the plastic packaging material which is not matched with the CTE of silicon can be effectively released; after the TSV copper columns are exposed, the plastic packaging material in the grooves is also exposed, and warping balance of the whole wafer is facilitated.

While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to persons skilled in the relevant art that various combinations, modifications, and changes can be made thereto without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention disclosed herein should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.