Abstract:
This invention discloses a composite distributed dielectric structure. It comprises one or more conductor layers, one or more dielectric layers distributed on the conductor layers, and one or more conductor traces distributed on the dielectric layers. One or more dielectric plates can be further around the conductor traces. The dielectric layers or plates may or may not have plural dielectric materials therein, respectively described in two embodiments. Each conductor trace lies on a dielectric material without crossing two different dielectric materials. Two or more dielectric layers may be stacked on the conductor layers The invention provides a low cost and practical dielectric structure for interconnect systems to reduce dielectric loss, cross talk, and signal propagation delay and to well control the impedance matching while maintaining proper heat dissipation and noise reduction at high frequency transmission.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention generally relates to dielectric structures used for interconnects systems, and more specifically to a composite distributed dielectric structure. It is applicable to interconnects systems at high-speed circuits.  
       BACKGROUND OF THE INVENTION  
       [0002]     The growing trend of more functionality and smaller form factor for electronic components has resulted in a dramatic increase of electrical interconnect density in integrated circuits (intra-chip interconnect), electronic packages and circuit boards (inter-chip interconnect). Dielectric layers in electronic circuits are employed as capacitors or circuit boards/substrates. High dielectric constant materials normally have better heat dissipative capability than the low dielectric constant materials, and therefore make them ideal for power components at high frequencies, such as microwave frequencies. A high dielectric constant material also leads to a large interconnect capacitance, which has pros and cons. In order to reduce simultaneous switching noise (SSN), high dielectric constant substrates are required for power and ground planes. However, signal lines surrounded by high dielectric constant materials can cause an increase of cross-talk, dielectric loss, and propagation delay at high frequency transmission. The dielectric loss is a result of the hysterical loop which is worse for high dielectric constant material than for low constant dielectric material. The propagation delay is due to the fact that the wavelength of a signal becomes shorter when it propagates through a material with a higher dielectric constant  
         [0003]     Transmission lines, including microstrip lines and strip lines, are important elements in microwave circuits. These lines not only provide interconnection between active and passive devices but also are utilized as an impedance matching element for the circuits. A microstrip line is a conductor trace routed as the top or bottom layer for example of a circuit board. A strip line is a conductor trace routed on the inside layer for example of a circuit board. The impedance of a transmission line is proportional to dielectric constants of surrounding materials and trace height, and inversely proportional to trace width and trace thickness. As the effective dielectric constant of a strip line is higher than that of a microstrip line, less dielectric loss can be achieved in a microstrip line than in a strip line. In order to better control the impedance matching of transmission lines in microwave circuits, low dielectric constant materials are therefore desired.  
         [0004]     In general, low dielectric constant materials are adopted for high speed and low loss transmission of signals but their poor heat dissipative capability may result in excessive heat and temperature. If a whole circuit is built on either a low or a high dielectric constant material, the circuit will then suffer heat dissipation and impedance matching problems or dielectric loss and propagation delay problems. In order to take advantage of their different material properties, both high and low dielectric constants materials must be chosen in different areas of a circuit board/substrate to meet specific requirements.  
         [0005]     Several techniques based on the layout of microstrip or strip line on the dielectric material have been developed to reduce the dissipation loss in microwave circuit applications. In U.S. Pat. No. 5,753,968, Bahl et al disclosed an off-chip interconnect scheme, wherein an add-on layer  101  of dielectric material between a strip conductor  103  and a substrate  102  to reduce the dissipation loss in monolithic microwave integrated circuits as shown in  FIG. 1 . The dielectric constant of the add-on layer  101  is less than that of the substrate  102 . The add-on dielectric layer  101  is disposed on top of the substrate  102  and placed at a different level (non-coplanar) from the substrate  102 . It is often formed by bonding a layer of low dielectric material onto the high dielectric substrate  102  using a conventional lamination method, and then followed by photolithographic and etching processes to define the circuit pattern. The yield is usually low. In this case, a whole layer of material is consumed just to meet one specific requirement. Therefore, the cost is high. Furthermore, the surface topology is rough and not good for subsequent manufacturing processes.  
         [0006]     In U.S. Pat. No. 5,604,017, Frankosky proposed a multi-dielectric laminate taking the advantage of both high and low dielectric material properties for off-chip interconnect layout of high frequency transmission circuits. The multi-dielectric laminate comprises a common conductor overlying materials having different dielectric constants laminated onto one continuous ground plane. By employing the continuous conductor and ground plane, it eliminates the need for constant impedance devices or conductor jumpers, and the top surface of the conductor may be printed and etched as a continuous piece, with allowances for the constant impedance lines across each dielectric.  
         [0007]     According to International Patent Publication WO 2004/079797, a high speed interconnect system was proposed for both on-chip and off-chip interconnects to reduce the microwave loss and the signal propagation delay. For on-chip interconnects, the signal lines  201  laid on the oxide or dielectric material  202  connect the high-speed electronics devices (not shown) on a semiconductor substrate  204 . For off-chip interconnects in a PCB, opened trenches or slots  203  are used to reduce the microwave loss of high-speed chips, as shown in  FIG. 2 . The trenches or slots may be filled up with air or low dielectric material. The trench or slot does not go all the way through the dielectric layer. The manufacturing process is difficult and the depth of trench or slot is hard to precisely control.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention has been made to overcome the aforementioned drawback of conventional dielectric structures used for interconnects systems. The primary object of the present invention is to provide a composite distributed dielectric structure for interconnects systems.  
         [0009]     In a first preferred embodiment of the present invention, a composite distributed dielectric structure comprises one or more conductor layers, one or more dielectric layers formed on the conductor layers, and one or more conductor traces formed on the dielectric layers. At least one dielectric layer has plural dielectric materials therein.  
         [0010]     In a second preferred embodiment of the present invention, the composite distributed dielectric structure further comprises one or more dielectric plates formed around the conductor traces. Wherein the dielectric layers or plates may or may not have plural dielectric materials therein.  
         [0011]     According to the invention, the dielectric layer or dielectric plate having plural dielectric materials therein has at least two dielectric constants. Each conductor trace does not across two different dielectric materials. In other words, each conductor trace lies on a dielectric material. The conductor traces on different dielectric layers are electrically connected through via holes. Two or more dielectric layers may be stacked on one conductor layer.  
         [0012]     An adhesive layer may be further attached between a conductor trace and a dielectric layer, or between a dielectric layer and a conductor layer. The composite distributed dielectric structure may be realized with a flexible laminate, a printed circuit board, or a substrate.  
         [0013]     In a first example of the first embodiment, the composite distributed dielectric comprises a conductor layer, a dielectric layer having plural dielectric materials, and a conductor trace overlying the dielectric layer. The dielectric layer is formed on the conductor layer. The dielectric layer has plural dielectric materials with different dielectric constants.  
         [0014]     In a second example of the first embodiment, the composite distributed dielectric comprises a conductor trace, two dielectric layers having plural dielectric materials in each layer, and a first and second conductor layers. The two dielectric layers are stacked between the two conductor layers. Each dielectric material in each dielectric layer may have a dielectric constant and a dielectric loss. The conductor trace is formed between the two stacked dielectric layers and lies on a dielectric material.  
         [0015]     In a third example of the first embodiment, the composite distributed dielectric structure is formed by bonding together one composite distributed dielectric structure of the first example on top of at least one composite distributed dielectric structure of the second example. These composite distributed dielectric structures can be electrically connected through via holes. The strip conductor lines of each composite distributed dielectric structure are normally routed perpendicularly to those of adjacent composite distributed dielectric structures.  
         [0016]     In a fourth example of the first embodiment, the composite distributed dielectric structure is formed by bonding together plural composite distributed dielectric structures of second examples. These composite distributed dielectric structures can be electrically connected through via holes. The strip conductor lines of each composite distributed dielectric structure are normally routed perpendicularly to those of adjacent composite distributed dielectric structures.  
         [0017]     In an example of the second embodiment, the composite distributed dielectric structure comprises two conductor layers, two dielectric layers, a conductor trace formed on the dielectric layer, and a dielectric plate formed around the conductor trace. The dielectric layer has plural dielectric materials therein.  
         [0018]     The fundamental structures provided in this invention can be used for high-speed connectors, high-speed cables, and intra-chip and inter-chip interconnects systems at high speed transmission. The present invention provides a low cost and practical dielectric structure for interconnect system to reduce dielectric loss, cross talk, and signal propagation delay and to well control the impedance matching while maintaining proper heat dissipation and noise reduction at high frequency transmission.  
         [0019]     The foregoing and other objects, features, aspects and advantages of the present invention will become better understood from a careful reading of a detailed description provided herein below with appropriate reference to the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]      FIG. 1  is a diagram of a conventional microstrip line on a substrate having different dielectric constants materials.  
         [0021]      FIG. 2  is a side view of a conventional interconnects system.  
         [0022]      FIG. 3A  is a diagram of the composite distributed dielectric structure in a first preferred embodiment according to the present invention.  
         [0023]      FIG. 3B  is a diagram of the composite distributed dielectric structure in a second preferred embodiment according to the present invention.  
         [0024]      FIG. 4A  is a side view of a first example of  FIG. 3A  according to the present invention.  
         [0025]      FIG. 4B  is a perspective view of the first example of  FIG. 3A  according to the present invention.  
         [0026]      FIG. 5A  is a side view of a second example of  FIG. 3A  according to the present invention.  
         [0027]      FIG. 5B  is a perspective view of the second example of  FIG. 3A  according to the present invention.  
         [0028]      FIG. 6  is a perspective view of a third example of  FIG. 3A  according to the present invention.  
         [0029]      FIG. 7  is a perspective view of a fourth example of  FIG. 3A  according to the present invention.  
         [0030]      FIG. 8  is a side view of a example of  FIG. 3B  according to the present invention.  
         [0031]      FIG. 9A  is a side view illustrating an adhesive layer is further attached between a conductor trace and a dielectric layer.  
         [0032]      FIG. 9B  is a side view illustrating an adhesive layer is further attached between a dielectric layer and a conductor layer.  
         [0033]      FIG. 10  shows the simulated signal attenuation in a conventional microstrip line and in a composite distributed dielectric structure according to the present invention, in which both low dielectric constant materials and conductors are therein. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0034]     In the invention, a composite distributed dielectric structure having different dielectric constants is provided to meet specific requirements in high frequency electronic circuits. Both high- and low-dielectric constants materials are chosen in different areas of a circuit board or substrate to meet specific applications.  FIG. 3A  is a diagram of the composite distributed dielectric structure in a first preferred embodiment according to the present invention.  
         [0035]     The composite distributed dielectric structure of  FIG. 3A  comprises one or more conductor layers, one or more dielectric layers distributed on the conductor layers, and one or more conductor traces distributed on the dielectric layers. At least one dielectric layer has plural dielectric materials therein.  
         [0036]     Referring to  FIG. 3A , the composite distributed dielectric structure  300  comprises conductor layers  311 - 31   n , dielectric layers  321 ,  322   a - 322   c ,  323   a , . . . ,  32   j  formed on the conductor layers  311 - 31   n , and conductor traces  331 ,  332 ,  333   a - 333   b ,  334 ,  33   m  formed on the dielectric layers  321 ,  322   a - 322   c ,  32   j.    
         [0037]     Dielectric layer  321  is formed on the conductor layer  311 , and the dielectric layer  321  has dielectric materials  341   a - 341   c  therein. Conductor trace  331  is formed on the dielectric layer  321 .  
         [0038]     Dielectric layers  322   a - 322   c  are stacked and formed on the conductor layer  312 . Conductor trace  332  is formed on the dielectric layer  322   b , and conductor traces  333   a - 333   b  are formed on the dielectric layer  322   c . Dielectric layer  322   a  has one dielectric material therein. Dielectric layer  322   b  has five dielectric materials therein. Dielectric layer  322   c  has three dielectric materials therein. Dielectric layer  323   a  has three dielectric materials therein.  
         [0039]     Conductor trace  32   m  is formed on the bottom dielectric layer  32   j . Dielectric layer  32   j  has three dielectric materials therein, and is formed on the bottom conductor layer  31   n.    
         [0040]     According to the invention, the dielectric layer having plural dielectric materials therein has at least two dielectric constants. These different dielectric materials may include high/low dielectric constant materials, FR4, and so on. The conductor traces lying on the different dielectric layers may be electrically connected through via holes. The conductor layer may be a metal layer. The composite distributed dielectric structure may be realized with a flexible laminate, a printed circuit board, or a substrate and the like.  
         [0041]     As can be seen from  FIG. 3A , a plurality of stacked dielectric layers may be formed between two conductor layers. Each conductor trace lies on a dielectric material without crossing two different dielectric materials.  
         [0042]     The manufacturing process for realizing the composite distributed dielectric structure of  FIG. 3A  is described as follows. The dielectric layer is disposed onto the conductor layer (e.g., aluminum or copper foil) to from a substrate (e.g., FR4). This can be done with a conventional lamination method. Then, at least one trench/slot is opened in the dielectric layer. Either a photolithographic process followed by a chemical etching process or a laser etching process can be adopted for the trench/slot opening. The trenches/slots are then filled up with different dielectric constant materials to meet specific applications. The filling process may be a printing or deposition process. Finally, the conductor layer is formed and defined on top of the dielectric layer. The formation of the conductor layer can be achieved with an electro-plating or lamination technique. The definition of the circuit pattern is usually performed with a photolithographic process and then followed by a chemical etching process.  
         [0043]      FIG. 3B  is a diagram of the composite distributed dielectric structure in a second preferred embodiment according to the present invention. The difference between the first and second embodiments is that one or more dielectric plates are further formed around the conductor traces in the second embodiment. Wherein the dielectric layers or plates may or may not have plural dielectric materials therein. Without loss of generality, two dielectric plates  351  and  352  are shown in the second embodiment. The dielectric plate  351  is formed around the conductor traces  333   a  and  33   b . The dielectric plate  352  is formed around the conductor traces  334 .  
         [0044]     In the second preferred embodiment shown in  FIG. 3B , each of the dielectric layers  322   a ,  322   d ,  322   e  and  323  has one dielectric material therein. This can be a special example of the second embodiment. According to the present invention, the dielectric layers may have plural dielectric materials therein, such as dielectric layers  321  and  32   j . The dielectric layer having plural dielectric materials therein has at least two dielectric constants. This has been illustrated in the first embodiment  
         [0045]     Further referring to  FIG. 3B , the dielectric plate  351  has one dielectric material therein. This can also be a special example of the second embodiment. According to the present invention, the dielectric plates may have plural dielectric materials therein, such as the dielectric plate  352 . The dielectric plate  352  has two dielectric materials  352   a  and  352   b  therein, and the two dielectric materials  352   a  and  352   b  have different dielectric constants.  
         [0046]     The preferred embodiments of the present invention will become better understood from the following examples with a detailed description provided herein below.  
         [0047]     The following four examples are taken from the first preferred embodiment shown in  FIG. 3A .  
         [0048]      FIG. 4A  is a side view of a first example of  FIG. 3A  according to the present invention. Referring to  FIG. 4A , the composite distributed dielectric structure  400  comprises a conductor layer  401 , a dielectric layer  402  having plural dielectric materials  402   a - 402   c  therein, and a conductor trace  403  formed on the dielectric layer  402  and without crossing two different dielectric materials. The dielectric layer  402  is formed on the conductor layer  401 .  FIG. 4B  is a perspective view of the first example of  FIG. 3A  according to the present invention.  
         [0049]      FIG. 5A  is a side view of a second example of  FIG. 3A  according to the present invention. Referring to  FIG. 5A , the composite distributed dielectric structure  500  comprises a first conductor layer  501 , a second conductor layer  505 , two dielectric layers  502  and  504  formed between the two conductor layers  501  and  505  and having plural dielectric materials in each layer, and a conductor trace  503  lying between the two dielectric layers  502  and  504 . Different dielectric materials  502   a - 502   c  in the dielectric layer  502  may have different dielectric constants. Different dielectric materials  504   a - 504   c  in the dielectric layer  504  may have different dielectric constants.  FIG. 5B  is a perspective view of the second example of  FIG. 3A  according to the present invention.  
         [0050]      FIG. 6  is a perspective view of a third example of  FIG. 3A  according to the present invention. Wherein the composite distributed dielectric structure is formed by bonding together one composite distributed dielectric structure of the first example on top of one or more composite distributed dielectric structures of the second example. These composite distributed dielectric structures can be electrically connected, such as through via holes  601 .  
         [0051]      FIG. 7  is a perspective view of a fourth example of  FIG. 3A  according to the present invention. Wherein the composite distributed dielectric structure is formed by bonding together plural composite distributed dielectric structures of the second example. Without loss of generality, two composite distributed dielectric structures of the second example is taken in the fourth example of  FIG. 3A . These composite distributed dielectric structures can be electrically connected, such as through via holes  701 .  
         [0052]     The strip conductor lines of each composite distributed dielectric structure are normally routed perpendicularly to those of adjacent composite distributed dielectric structures.  
         [0053]     The following example is taken from the second preferred embodiment shown in  FIG. 3B .  
         [0054]      FIG. 8  is a side view of an example of  FIG. 3B  according to the present invention. Referring to  FIG. 8 , the composite distributed dielectric structure comprises two conductor layers  811 - 812 , two dielectric layers  821 - 822 , a conductor trace  831  formed on the dielectric layer  822 , and a dielectric plate  851  formed around the conductor trace  832 . The dielectric layer  822  has plural dielectric materials  841   a - 841   c  therein. The conductor trace  831  on the dielectric layer  822  does not cross two different dielectric materials.  
         [0055]     According to the invention, an adhesive layer may be further attached between a conductor trace and a dielectric layer, or between a dielectric layer and a conductor layer.  FIG. 9A  illustrates an adhesive layer  901  is further attached between a conductor trace  902  and a dielectric layer  903 .  FIG. 9B  illustrates an adhesive layer  901  is further attached between a dielectric layer  903  and a conductor layer  904 .  
         [0056]      FIG. 10  shows the simulated signal attenuation in a conventional microstrip line and in a composite distributed dielectric structure according to the present invention, in which both low dielectric constant materials and conductors are therein. The horizontal axis represents operating frequency, and the vertical axis represents signal attenuation. It can be dearly seen that the composite distributed dielectric structure of the present invention provides a lower dielectric loss than the conventional microstrip line. And, the differences between them increase with increasing frequency.  
         [0057]     Although the present invention has been described with reference to the preferred embodiments, it will be understood that the invention is not limited to the details described thereof. Various substitutions and modifications have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.