201039708 六、發明說明： 【發明所屬之技術領域】 [0001] 本發明係關於一種軟性電路板，尤指一種可傳輸高速差 分訊號的軟性電路板。 【先前技術】 [0002] 軟性電路板是用柔性的絕緣基材製成的印刷電路板，具 有許多硬性印刷電路板不具備的優點。例如軟性電路板 厚度較薄，可以自由彎曲、捲繞、折疊，可依照空間佈 局要求任意安排，並在三維空間任意移動和伸縮，從而 達到元器件裝配和導線連接的一體化。利用軟性電路板 可大大縮小電子產品的體積，適用電子產品向高密度、 小型化、高可靠性方向發展的需要。因此，軟性電路板 在航天、軍事、移動通訊、手提電腦、電腦週邊、PDA、 數碼相機等領域或產品上得到了廣泛的應用。 [0003] 因為軟性電路板厚度極薄，軟性電路板上的傳輸線的阻 抗偏低，因為傳輸高速訊號要求較高的傳輸線阻抗，在 軟性電路板上，即使一般製程可達到的最細傳輸線寬度 ，例如4密爾（1密爾= 0.0254毫米），也難以達到高速 訊號傳輸線阻抗的要求。 [0004] 參考圖1，習知技術提高傳輸線阻抗的方法，是將軟性電 路板50的接地層參考銅箔切割成網格狀。但如果在訊號 層上傳輸差分對51時，會因為差分傳輸線52和差分傳輸 線54對應的接地層銅箔網格排佈不同，導致共模噪音的 產生，這也是一般軟性電路板無法傳輸高速差分訊號的 原因。 098113093 表單編號A0101 第4頁/共10頁 0982021881-0 201039708 【發明内容】 [0005] 鑒於上述内容，有必要提供一種可傳輸高速差分訊號的 軟性電路板。 [0006] 一種軟性電路板，包括至少一訊號層，該訊號層的上方 和下方分別設有一接地層，該訊號層與相鄰的接地層之 間分別設有一絕緣介質層，該訊號層上佈設一差分對， 該差分對包括兩條差分傳輸線，該兩絕緣介質層的相對 介電常數不同，每一接地層上與該差分對垂直相對的部 分為一挖空區域，該兩接地層上挖空區域的兩邊緣分別 〇 與其相鄰的差分傳輸線間具有一第一水平間距及一第二 水平間距，且該第一水平間距與該第二水平間距不相等 0 [0007] 該軟性電路板是在該接地層上，將與該差分對垂直對應 的兩相鄰接地層部分挖空，避免差分對與相鄰接地層的 間距太近所導致的傳輸線阻抗偏低問題的產生。本發明 軟性電路板可傳輸高速訊號，並消除習知技術中網格化 Q 接地層所衍生的共模噪音問題。本發明軟性電路板無需 增加額外成本，只需調整習知佈線方式即可實現。 【實施方式】 [0008] 請參照圖2，本發明軟性電路板的較佳實施方式包括一訊 號層10及分別位於該訊號層10上、下的兩接地層30，在 訊號層10及每一接地層30之間設有一絕緣介質層20。其 中，該兩絕緣介質層20的相對介電係數不同，即由兩種 不同性質的絕緣介質構成，該兩絕緣介質層20的厚度可 以相同也可以不同。 098113093 表單編號A0101 第5頁/共10頁 0982021881-0 201039708 [0009] 差刀對11包括兩條差分傳輸線12及14，並佈線於該訊 號層10上。每—接地層30上，與該差分傳輸線丨2及14所 垂直相對的部分作挖空處理，以避免差分對11與相鄰接 地層30之間的垂直距離太近所導致的傳輸線阻抗偏低問 題的產生，上層接地層30未挖空的部分與其相鄰差分傳 輪線12或14具有一第一水平間距dl，下層接地層3〇未挖 空的部分與其相鄰差分傳輸線12或14具有一第二水平間 距d2，該第—水平間距“與該第二水平間距犯不相等，201039708 VI. Description of the Invention: [Technical Field] [0001] The present invention relates to a flexible circuit board, and more particularly to a flexible circuit board capable of transmitting a high speed differential signal. [Prior Art] [0002] A flexible circuit board is a printed circuit board made of a flexible insulating substrate, which has many advantages that a rigid printed circuit board does not have. For example, the flexible circuit board has a thin thickness and can be freely bent, wound, and folded. It can be arbitrarily arranged according to the space layout requirements, and can be arbitrarily moved and expanded in a three-dimensional space, thereby achieving integration of component assembly and wire connection. The use of a flexible circuit board can greatly reduce the size of electronic products, and is suitable for the development of electronic products in the direction of high density, miniaturization, and high reliability. Therefore, flexible circuit boards have been widely used in aerospace, military, mobile communications, laptop computers, computer peripherals, PDAs, digital cameras and other fields or products. [0003] Because the thickness of the flexible circuit board is extremely thin, the impedance of the transmission line on the flexible circuit board is low, because the transmission of the high-speed signal requires a higher transmission line impedance, and on the flexible circuit board, even the finest transmission line width that can be achieved by a general process, For example, 4 mils (1 mil = 0.0254 mm), it is also difficult to achieve high-speed signal transmission line impedance requirements. Referring to FIG. 1, a conventional method for improving the impedance of a transmission line is to cut a ground layer reference copper foil of a flexible circuit board 50 into a grid shape. However, if the differential pair 51 is transmitted on the signal layer, the ground layer copper foil grid corresponding to the differential transmission line 52 and the differential transmission line 54 may be arranged differently, resulting in common mode noise, which is also a general flexible circuit board cannot transmit high speed differential. The reason for the signal. 098113093 Form No. A0101 Page 4 of 10 0982021881-0 201039708 SUMMARY OF THE INVENTION [0005] In view of the above, it is necessary to provide a flexible circuit board that can transmit high-speed differential signals. [0006] A flexible circuit board includes at least one signal layer, and a ground layer is disposed above and below the signal layer, and an insulating dielectric layer is disposed between the signal layer and the adjacent ground layer, and the signal layer is disposed on the signal layer a differential pair comprising two differential transmission lines, wherein the two dielectric layers have different relative dielectric constants, and a portion of each of the ground layers perpendicular to the differential pair is a hollowed out area, and the two ground layers are dig The two edges of the empty area respectively have a first horizontal spacing and a second horizontal spacing between the adjacent differential transmission lines, and the first horizontal spacing is not equal to the second horizontal spacing. [0007] The flexible circuit board is On the ground layer, two adjacent ground layer portions corresponding to the differential pair are hollowed out to avoid the problem of low transmission line impedance caused by the distance between the differential pair and the adjacent ground layer being too close. The flexible circuit board of the present invention can transmit high speed signals and eliminate the common mode noise problem caused by the gridded Q ground layer in the prior art. The flexible circuit board of the present invention can be realized by adjusting the conventional wiring method without adding extra cost. [0008] Referring to FIG. 2, a preferred embodiment of the flexible circuit board of the present invention includes a signal layer 10 and two ground layers 30 respectively located above and below the signal layer 10, in the signal layer 10 and each. An insulating dielectric layer 20 is disposed between the ground layers 30. The two dielectric layers 20 have different relative dielectric constants, that is, two different kinds of insulating materials, and the thickness of the two insulating dielectric layers 20 may be the same or different. 098113093 Form No. A0101 Page 5 of 10 0982021881-0 201039708 [0009] The differential blade pair 11 includes two differential transmission lines 12 and 14 and is routed to the signal layer 10. On each of the ground layer 30, a portion perpendicular to the differential transmission lines 丨2 and 14 is hollowed out to avoid a low transmission line impedance caused by the vertical distance between the differential pair 11 and the adjacent ground layer 30 being too close. The portion of the upper ground layer 30 that is not hollowed out has a first horizontal spacing dl with its adjacent differential transmission line 12 or 14, and the portion of the lower ground layer 3 that is not hollowed out has a first differential transmission line 12 or 14 a second horizontal spacing d2, the first horizontal spacing "does not equal to the second horizontal spacing,
圖2中每一接地層30上覆蓋的材料為銅箔，其中央的矩形 挖空區域32即是將接地層30上的銅箔挖空所形成的。在 該訊號層10上，該差分對Η的兩側平行設置有與差分對 11長度相等的接地導電材料，本較佳實施方式中該兩接 地導電材料為銅箔16，每一接地銅箔16與其對應相鄰的 傳輸線12及14具有一第三水平間距d。該第―、第二及第 二水平間距dl、d2及d根據差分對11傳輸的訊號不同而不 同，該第一、第二及第三水平間距以、（12及(1可根據差分 對11傳輸不同訊號時的阻抗要求，考慮軟性電路板上每 條差分傳輸線12及14的線寬、該兩差分傳輸線12及14的 間距、該訊號層10上接地銅箔16的寬度、該兩絕緣介質 層20的厚度、該兩絕緣介質層2〇的相對介電常數等參數 經由仿真軟體仿真後確定。其他實施方式中，也可不在 該訊號層10上佈設接地銅箔，僅透過調整該第一及第二 水平間距dl及d2來調整該兩差分傳輸線12及14的阻抗， 以實現高速差分訊號的傳輸。 [0010]該軟性電路板是在佈有差分對11的訊號層10的上下兩相 098113093 表單編號A0101 第6頁/共1〇頁 0982021881-0 201039708 Ο [0011] 鄰的接地層3 0上’將與差分對η的兩傳輸線I〗、η垂直 對應的部分挖空’避免差分對11與相鄰接地層30的間距 太近所導致的傳輪線阻抗偏低問題的產生，並選擇性地 在差分對11的兩側平行設置接地銅箔16，透過仿真軟體 仿真後設定每—接地層30未挖空的部分與其相鄰差分傳 輸線12或14的第一及第二水平間距dl及d2，以及該兩接 地銅箔16與傳輸線12、14的第三水平間距d。本發明軟性 電路板可傳輪高速訊號，並消除習知技術中網格化接地 層所衍生的共模噪音問題。本發明軟性電路板無需增加 額外成本’只需調整習知佈線方式gp可實現。 综上所述，本發明符合發明專利要件，爰依法提出專利 申請。惟，以上所述者僅為本發明之較佳實施例，舉凡 熟悉本案技藝之人士，在爰依本發明精神所作之等效終 飾或變化，皆應涵蓋於以下之申請專利範圍内。 [0012] ❹[0013] [0014] 【圖式簡單說明】 圖2係本發明軟性電路板較佳實施方式的結構示意圖 圖1係習知軟性電路板的結構示意圖。 【主要元件符號說明】 訊號層 10 差分傳輸線 12 絕緣介質層 20 挖空區域 32 14The material covered on each of the ground layers 30 in Fig. 2 is a copper foil, and the central rectangular hollowed out area 32 is formed by hollowing out the copper foil on the ground layer 30. On the signal layer 10, the two sides of the differential pair are provided with a grounding conductive material having the same length as the differential pair 11. In the preferred embodiment, the two grounded conductive materials are copper foils 16, and each of the grounded copper foils 16 is provided. The transmission lines 12 and 14 adjacent thereto have a third horizontal spacing d. The first, second, and second horizontal spacings dl, d2, and d are different according to signals transmitted by the differential pair 11, and the first, second, and third horizontal spacings are (12 and (1 can be based on the differential pair 11) For the impedance requirements when transmitting different signals, consider the line width of each differential transmission line 12 and 14 on the flexible circuit board, the spacing of the two differential transmission lines 12 and 14, the width of the ground copper foil 16 on the signal layer 10, and the two insulating mediums. The thickness of the layer 20 and the relative dielectric constant of the two insulating dielectric layers 2 are determined by simulation software simulation. In other embodiments, the ground copper foil may not be disposed on the signal layer 10, and only the first adjustment is performed. And the second horizontal spacing dl and d2 adjust the impedance of the two differential transmission lines 12 and 14 to realize the transmission of the high-speed differential signal. [0010] The flexible circuit board is the upper and lower phases of the signal layer 10 on which the differential pair 11 is disposed. 098113093 Form No. A0101 Page 6/Total 1 Page 0982021881-0 201039708 Ο [0011] The adjacent ground plane 30 0' will be hollowed out with the two transmission lines I of the differential pair η, η vertically corresponding to the 'differential pair 11 and adjacent ground plane If the pitch of 30 is too close, the problem of low impedance of the transmission line is generated, and the ground copper foil 16 is selectively disposed on both sides of the differential pair 11, and the grounding layer 30 is not hollowed out after simulation by simulation software. The first and second horizontal spacings d1 and d2 of the adjacent differential transmission line 12 or 14 and the third horizontal spacing d between the two grounded copper foils 16 and the transmission lines 12 and 14. The flexible circuit board of the present invention can transmit high-speed signals And eliminating the common mode noise problem derived from the gridded ground layer in the prior art. The flexible circuit board of the present invention does not need to add extra cost 'just need to adjust the conventional wiring mode gp can be realized. In summary, the present invention conforms to the invention. Patent requirements, patent applications are filed according to law. However, the above is only a preferred embodiment of the present invention, and those skilled in the art will be able to cover the equivalent finishes or changes in accordance with the spirit of the present invention. [0012] [0014] [0014] [Brief Description of the Drawings] FIG. 2 is a schematic structural view of a preferred embodiment of the flexible circuit board of the present invention. FIG. 1 is a conventional flexible circuit. The structure of FIG. [20] The main reference numerals DESCRIPTION hollowed area signal 10 the differential transmission line layer 12 the insulating dielectric layer 3214
接地銅箱Grounded copper box
098113093 表單編號A0101 第7頁/共1〇頁 0982021881-0098113093 Form No. A0101 Page 7 of 1 Page 0982021881-0