1315171 九、發明說明： 【發明/斤屬之技術領域】 本發明涉及一種製作柔性電路板之方法，尤其涉及— 種製作具有斷差結構之柔性電路板之方法。 "— 【先前技術】 柔性電路板（Flexible printed Circuit B〇ard，fpcb)以其 優異之抗徺曲性能廣泛應用於各種工作時部件之間存在相 對運動之電子産品巾以提供電力/訊號傳輸。例如折疊式手 #機，列印頭，硬碟機讀取頭中。 . =産品小型化之趨勢需要同樣面積電路板所能傳輸 之訊號量越來越高，於不能增加電路板面積之情形下若要 •提高信號傳輸量只能增加線路之層數。但層數增加，則其 抗撓曲性能降低，柔性電路板之壽命也降低。因此有必要 開發出具有優異之抗撓曲性能多層柔性電路板。 參閱圖18，爲一種具有斷差結構之柔性電路板結構示 籲思圖，柔性電路板於不同之區域具有不同之層數，層數少 之區域具有高之抗撓曲性能，層數高之區域可提高同樣面 積之電路板中之線路密度。 參閱圖18-圖23’爲先前技術中積層法製作此種柔性電 路板之方法示意圖。參閱圖18及圖19，將第一覆銅層壓板 (Copper Clad Laminate，CCL) 41、第一粘合層 45、第二 覆銅層壓板42疊層、壓合。參閱圖2〇及圖21，壓合後， 於第一覆銅層壓板41及第二覆銅層壓板42上貼上幹獏以 蝕刻線路。蝕刻線路時，先於第一覆銅層壓板41及第二覆 7 1315171 銅層屢板42上分別貼一層幹膜412、422,但由 層麼板-41與第二覆銅層壓板42長度不—致，一= 層壓板.41與第二覆銅層壓板42之間存在一個斷I::銅 二構附近幹臈412結構f曲而不能緊密貼合㈣-覆銅㈣板41及第二覆銅層㈣42之表面，^一 孔隙46’於崎驟時，钱刻藥水從此孔隙46;;!7: :第-覆銅制…第二覆銅層壓…:::： 應，造成銅層爆肖，剝離之問題。 層反 參閱圖22,再分別於第—覆銅層壓板41及第 异 壓板42上積層第—覆銅層難㈡及第二覆銅層壓板^ 述幹膜法再蝴線路。以此類推，可重複 至得到預定層數之電路板。 、狂直 护成導^於传到預定層數之電路板後，於電路板上 化成¥通孔47。形成導通騎需要於鑽狀孔⑽上導電 :於電層時，第二覆銅層壓板42部分絕緣層表面暴 路；電鐘樂水中，從而於絕緣層表面形成銅屑Μ。而 一覆銅層壓板43 及苐-額層驗44上製作最外層線路 日匕思…、第—覆銅層壓板42之樹脂層，會用幹膜貼於樹 :曰亡’但銅屑48會刺穿幹膜，如果第二覆銅層壓板C 又面s覆有銅箔，則蝕刻藥水蝕刻銅層造成斷線。 有鑒於此，有必要提供一種於製作過程中避免對柔性 2板：部銅層與絕緣層產生損害，並且可形成具有斷差 結構之製作柔性電路板之方法。 1315171 【發明内容】 以下以實施例說明於製作過程中避免對柔性電路板内 部銅層與絕緣層産生損害，並且可形成具有斷差結構之製 作柔性電路板之方法。 該方法包括以下㈣：提供第―覆銅職板、黏接層及 第一_層屢板，該第—覆銅隸板包括絕緣層及形成於其 上之銅fl ’第二覆銅層麗板包括絕緣層、形成於絕緣層上之 :荡及截止層；於該黏接層上預定區域形成開口，該黏接層 已括-靠近該開口之側邊；將第一覆銅層壓板、黏接層及第 :覆=壓碰次疊層縣合，使得職止層與該黏接層連 得咖ί —覆銅層壓板及第二覆銅層壓板的㈣上形成線路 =聽電路板；利用雷射對準該侧邊切割預製電路板中處 ^一覆_壓板—側之各層形成—切口；沿預定之邊界裁 路板形成一側面，該側面與該切口於該預製電： = 與朗口相對應之去除區，該去除區於該斷面 構之柔性電路板。 脫洛從而形成-具有斷差結 之方先前技術，該製作具有斷差結構之柔性電路板 孔時i玫Γ下優點：首先，於電路板上形成線路或者通 孔0TJ· ’電路板上並益斷差社槐 斷線算;/ 此可以避免銅層剝離、 形成绩玫，可提向産品良率。其次’於電路板上 者通孔時，電路板上也無預先形成之刀口，可 線路或者通孔時藥水從刀口中侵入，造成電路板 最後’利用雷射進行切割可以得到更加精確之斷面 1315171 尺寸。 【實施·方式】 以·下結合圖1 -圖11對本技術方案第一實施例之製作具 有斷差結構之電路板之方法作出詳細說明。 參閱圖1，首先，提供第一覆輞層壓板（c〇pperClad Laminate，CCL) 11、第二覆銅層壓板12及黏接層15，並 於黏接層15上形成一開口 152,黏接層15於開口 152處有 一侧邊154。根據需要，開口 152可爲各種形狀，例如矩形、 圓形、方形。本實施例中開口 152形狀爲矩形。第一覆銅 層壓板11包括絕緣層111及形成於絕緣層in上之銅猪 112。第二覆銅層壓板12包括絕緣層121及分別形成於絕 緣層121兩表面上之銅箔122及銅靖124。 絕緣層111、絕緣層121及黏接層15最常用之材質爲 聚酰亞胺（Polyimide，PI) ’但還可選自以下聚合物如鐵氟龍 (Teflon)、聚硫胺（Polyamide)、聚甲基丙婦酸甲酯 (Polymethylmethacrylate)、聚礙酸酯（Polycarbonate)、聚乙 烯對苯二酸醋（Polyethylene Terephtalate，PET)或聚酰亞胺-聚乙烯-對苯二甲酯共聚物 （Polyamide polyethylene-terephthalate copolymer)或者其組合物。覆銅 廣麼板也可以用其他覆銅層壓板代替’如銀、金等。銅猪 或者其他金屬箔一般藉由沈積之方法如電鍍、濺鍍，或者 壓合之方法形成於絕緣層上。 參閱圖2,將第一覆銅層壓板11、黏接層15及第二覆 銅層壓板12依次疊層並壓合。疊層時絕緣層111及截止銅 1315171 箔124分別緊貼於黏接層15之兩表面上。 參-閱圖3,於銅箔112及銅箔122上形成線路並於銅箔 112上與侧邊154相對應之區域形成一穿透銅箔112之凹槽 114。形成線路時可採用蝕刻工藝，其具體包括貼幹膜（Dry Film)、曝光、顯影、蝕刻等步驟。凹槽114可以與線路同 時蝕刻形成，也可於形成線路之前或者形成線路之後以摻 鈦釔鋁石榴石（Nd:YAG)雷射燒蝕而製成。 參閱圖4，於銅箔112上依次疊層黏接層16及第一覆 _銅層壓板13,於第二銅箔122上疊層黏接層17及第二覆銅 層壓板14，然後壓合。第一覆銅層壓板13包括絕緣層131 及形成於絕緣層131上之銅箔132。第二覆銅層壓板14包 括絕緣層141及形成於絕緣層141上之銅箔142。絕緣層 131與黏接層16相鄰。絕緣層141與黏接層17相鄰。 參閱圖5，形成導通孔18以導通銅箔112，銅箔122， 銅箔132及銅箔142。導通孔18可採用機械鑽孔或者雷射 •燒孔（Laser-ablation)等方式形成。導通孔18内壁上可艘上 導電層，如鍍上一層銅。或者於導通孔18内填充導電膠。 本實施例當中，導通孔18内壁上鍍有銅層。 參閱圖6,於銅箔132及銅箔142上形成線路並同時於 銅箔132上與側邊154及凹槽114相對應之區域形成凹槽 134得到預製電路板19。凹槽134可以與線路同時蝕刻形 成，也可於形成線路之前或者形成線路之後以Nd:YAG雷 射燒出。 一併參閱圖7及圖8,以二氧化碳雷射對準凹槽134 11 1315171 切割絕緣層131、黏接層16及絕緣層111形成切口 191。 一般情.況下，二氧化碳雷射於絕緣層/黏接層中鑽孔時之鑽 孔速度狠快，惟其波長不同於能被銅箔吸收之波長，因此銅 箔124不能被二氧化碳雷射切割，從而可以作爲截止層， 當切割完絕緣層111後，銅箔124可防止二氧化碳雷射進 一步向下切割。 圖9係圖10中之預製電路板之俯視示意圖。邊界192 内之部分爲最終成品電路板所在之區域。參閱圖9，沿邊界 ❿192裁切預製電路板19去除預製電路板19上邊界192以外 之部分。裁切後於預製電路板19上形成侧面194。參閱圖 _ 11，側面194以及切口 191共同於預製電路板19上圍成去 除區193。而此時由於去除區193剛好對應於開口 152上， 去除區193也就與預製電路板19之間脫離連結關係。去除 區193即可從預製電路板19上脫脫落而得到具有斷差結構 之柔性電路板100。裁切時可採用模具沖切或者刀具切割等 籲方式。 本實施例當中，銅箔112及銅箔132中分別形成凹槽 114及凹槽134，因此二氧化碳雷射可以順利切割絕緣層 111、絕緣層131及黏接層16，由於截止銅箔124之存在， 可防止二氧化碳雷射進一步向下切割而破壞電路板100。 本實施當中形成的為部分區域爲四層，另一部分區域 爲兩層之柔性電路板。然而於第一覆銅層壓板11、粘接層 15及第二覆銅層壓板12壓合並形成線路之後，即可利用雷 射切割第一覆銅層壓板11從而得到一部分爲兩層，一部分 12 1315171 .爲早層之柔性電路板。或者於第—覆銅層壓板i3與第 銅壓板]4上還積層另外的覆銅層壓板。其他處理過程= 與第-實施例之製作具有斷差結構之柔性電路板之: 似。 本實施例當中，於黏接層15兩表面上分別積 壓板並在覆銅層壓板的銅箱上形成線路。可選的，也= 積層已經預先形成有線路的覆銅層壓板。其他的製程 一實施例相似。 & 相較於先前技術，本實施例之製作具有斷差姓構之柔 性電路板之方法具有如下優點：首先，於電路板：形成線 路或者通孔時，電路板上並無斷差結構，因此可以避免銅 層剝離、斷線等不良之産生，可提高産品良率。其次，於 電路板上職線路或者軌時，電路板上也無縣形成之 刀口，可避免形成線路或者通孔時藥水從刀口中侵入，造 成電路板不良。最後，利用雷射進行切割可以得到更加= 確之斷面尺寸。 、 第二實施例之製作具有斷差結構之柔性電路板之方法 與第一實施例相似，不同之處在於，參閱圖12，第二覆銅 層壓板22包括緣層221，形成於絕緣層221上之銅箔=22 及截止層224。截止層224形成於與側邊254對齊之部分區 域内。截止層224之材料可選自金屬如鉻、銅、鋁等:截 止層224可以用電鍍或者濺鍍之方法形成於第二絕緣層 時，製作截止層224時，事先貼上一層掩膜，露出要形^ 截止層224之區域，再進行電鍍或者係濺鍍。當形成截止 13 1315171 層？24之後即可將掩膜去除。 參-閱圖13，截止層224所起作用與銅箔124相似，防 止雷射_完成切割任務後進一步破壞電路板。利用截止層224 取代銅fl 124’則電路板可以做的更薄，其抗撓曲性能也更 強。 第三實施例之製作具有斷差結構之柔性電路板之方法 與第二實施例相似，不同之處在於，於銅箔312、銅箔3% 上並不形成與側邊354對齊之凹槽。 # 參閱圖14至圖17,當形成預定層數之預製電路板之 後，以兩種不同之雷射對準側邊354進行切割，其中第一 雷射381用於切割銅箔312及銅箔332，第二雷射382用於 切割黏接層36、絕緣層311及絕緣層331。第一雷射爲固 體雷射如Nd:YAG雷射，第二雷射爲氣體雷射如二氧化碳 =射。由於Nd:YAG雷射適合切割銅箱，但其頻率不同於 緣層311或者黏制36材質，因此很難切割絕緣層奶 鲁或者黏接層36，而二氧化碳雷射剛好與此相反。 綜上所述，本發明確已符合發明專利之要件，遂依法 =出專财請。惟’以上所述者僅為本發明之較佳實施方 ，γ自不能以此限制本案之申請專利範圍。舉凡熟悉本案 技藝之人士援財發明之精神所作之等效修飾或變比、 應涵蓋於以下申請專利範圍内。 白 【圖式簡單說明】 圖1至圖11係第一實施例之製作具有斷差結構之柔性 14 1315171 電路板之方法示意圖。 圖-12至圖13係第二實施例之製作具有斷差結構之柔 性電路板之方法示意圖。 圖14至圖17係第三實施例之製作具有斷差結構之柔 性電路板之方法示意圖。 圖18至圖23係先前技術製作具有斷差結構之柔性電 路板之方法示意圖。 【主要元件符號說明】 111,211,121,221,131,331,141 112,212,312,122,222,132,332,142,124 15,25,16,36,17 154,254,354 114,134 導通孔 18 19 切口 191 192 側面 194 224 第一雷射 381 382 _第一覆銅層壓板11，13,21 第二覆銅層壓板 12, 14,22 *絕緣層 銅猪 黏接層 側邊 凹槽 φ預製電路板 邊界 截止層 第二雷射 151315171 IX. INSTRUCTIONS: [Technical Field of the Invention] The present invention relates to a method of fabricating a flexible circuit board, and more particularly to a method of fabricating a flexible circuit board having a stepped structure. "— [Prior Art] Flexible printed circuit B〇ard (fpcb) is widely used in various kinds of electronic products with relative motion between components to provide power/signal transmission with its excellent anti-twist performance. . For example, a folding hand #machine, a print head, and a hard disk drive read head. The trend of product miniaturization requires that the amount of signals that can be transmitted by the same area of the board is getting higher and higher. If the board area cannot be increased, the signal transmission amount can only increase the number of layers of the line. However, as the number of layers is increased, the flexural resistance is lowered and the life of the flexible circuit board is also lowered. Therefore, it is necessary to develop a multilayer flexible circuit board having excellent flexural resistance. Referring to FIG. 18, there is shown a schematic diagram of a flexible circuit board structure having a fault structure. The flexible circuit board has different layers in different regions, and the region with a small number of layers has high flexural resistance and a high number of layers. The area increases the line density in the same area of the board. Referring to Figures 18 - 23', there is shown a schematic view of a method of fabricating such a flexible circuit board by the lamination method of the prior art. Referring to Figures 18 and 19, a first copper clad laminate (CCL) 41, a first adhesive layer 45, and a second copper clad laminate 42 are laminated and pressed. Referring to Fig. 2A and Fig. 21, after pressing, a dry enamel is applied to the first copper clad laminate 41 and the second copper clad laminate 42 to etch the wiring. When the circuit is etched, a dry film 412, 422 is applied on the copper-clad laminate 41 and the second cladding 7 1315171, respectively, but the length of the laminate-41 and the second copper-clad laminate 42 No--, one = there is a break between the laminate .41 and the second copper-clad laminate 42. I:: near the copper two-structure, the dry 412 structure f is curved and cannot be closely fitted (four)-copper (four) plate 41 and The surface of the second copper-clad layer (4) 42, ^ a hole 46' in the case of the sacrificial, the money engraved from the pores 46;;! 7: : the first - copper-clad... the second copper-clad laminate...:::: should, cause The copper layer is bursting and the problem of stripping. Layer Reverse Referring to Fig. 22, the first copper-clad laminate 41 and the second copper-clad laminate are laminated on the first copper-clad laminate 41 and the first differential pressure plate 42, respectively, and the second copper-clad laminate is described. By analogy, it can be repeated to obtain a predetermined number of layers of the board. After being passed to the circuit board of the predetermined number of layers, it is turned into a through hole 47 on the circuit board. The formation of the conductive ride requires conduction on the drilled hole (10): when the electric layer is on, the surface of the second copper clad laminate 42 is insulated from the surface of the insulating layer; the electric clock is in the water, thereby forming a copper crucible on the surface of the insulating layer. On the other hand, a copper-clad laminate 43 and a 苐-front layer inspection 44 are used to make the outermost layer of the 匕 匕 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 The dry film is pierced. If the second copper clad laminate C is coated with copper foil, the etching solution etches the copper layer to cause disconnection. In view of the above, it is necessary to provide a method of fabricating a flexible circuit board having a hysteresis structure by avoiding damage to the flexible 2 board: the copper layer and the insulating layer during the manufacturing process. 1315171 SUMMARY OF THE INVENTION The following is an embodiment to avoid damage to the copper layer and the insulating layer inside the flexible circuit board during the manufacturing process, and a method of manufacturing a flexible circuit board having a stepped structure can be formed. The method comprises the following (4): providing a first copper clad plate, an adhesive layer and a first layer of a plurality of plates, the first copper-clad plate comprising an insulating layer and a copper fl 'second copper-clad layer formed thereon The board includes an insulating layer formed on the insulating layer: a swash layer and a cut-off layer; a predetermined area is formed on the adhesive layer to form an opening, the adhesive layer includes a side adjacent to the opening; and the first copper clad laminate, Adhesive layer and the first: the cover = the pressure of the laminated county, so that the service layer and the adhesive layer are connected to the copper-clad laminate and the second copper-clad laminate (four) on the line = listening to the circuit board Aligning the side of the prefabricated circuit board with a laser to form a slit in the side of the side of the prefabricated circuit board; forming a side along the predetermined boundary of the cutting board, the side and the slit in the prefabrication: A removal zone corresponding to the Langkou, the removal zone being a flexible circuit board constructed in the section. De-loating to form a prior art with a faulty junction, the advantage of making a flexible circuit board hole with a faulty structure is as follows: First, a circuit or a via hole is formed on the circuit board 0TJ·' The break-off of the company is broken; / This can avoid the peeling of the copper layer, the shape of the results, and can improve the yield of the product. Secondly, when there is a through hole on the circuit board, there is no pre-formed knife edge on the circuit board. When the circuit or the through hole is inserted, the syrup invades from the knife edge, causing the circuit board to finally use the laser for cutting to obtain a more accurate section. 1315171 size. [Embodiment] A method of manufacturing a circuit board having a stepped structure according to the first embodiment of the present technical solution will be described in detail with reference to Figs. 1 to 11 . Referring to FIG. 1 , firstly, a first copper clad laminate (CCL) 11 , a second copper clad laminate 12 and an adhesive layer 15 are provided, and an opening 152 is formed on the adhesive layer 15 for bonding. Layer 15 has a side 154 at opening 152. The opening 152 can be of various shapes, such as rectangular, circular, square, as desired. The opening 152 is rectangular in shape in this embodiment. The first copper clad laminate 11 includes an insulating layer 111 and a copper pig 112 formed on the insulating layer in. The second copper clad laminate 12 includes an insulating layer 121 and copper foils 122 and Tongshui 124 respectively formed on both surfaces of the insulating layer 121. The most commonly used material for the insulating layer 111, the insulating layer 121 and the adhesive layer 15 is polyimide (PI) 'but may also be selected from the following polymers such as Teflon, Polyamide, Polymethylmethacrylate, Polycarbonate, Polyethylene Terephtalate (PET) or Polyimide-Polyethylene-terephthalate Copolymer ( Polyamide polyethylene-terephthalate copolymer) or a combination thereof. Copper-clad laminates can also be replaced by other copper-clad laminates such as silver and gold. Copper pigs or other metal foils are typically formed on the insulating layer by deposition methods such as electroplating, sputtering, or lamination. Referring to Fig. 2, the first copper clad laminate 11, the adhesive layer 15, and the second copper clad laminate 12 are laminated in this order and pressed. The insulating layer 111 and the cut-off copper 1315171 foil 124 are adhered to both surfaces of the adhesive layer 15, respectively. Referring to Figure 3, a line is formed on the copper foil 112 and the copper foil 122 and a recess 114 is formed in the copper foil 112 corresponding to the side 154 to penetrate the copper foil 112. An etching process may be employed to form the wiring, which specifically includes steps of dry film, exposure, development, etching, and the like. The recess 114 may be formed by etching simultaneously with the wiring, or may be formed by ablation of titanium-doped yttrium aluminum garnet (Nd:YAG) before or after forming the wiring. Referring to FIG. 4, the adhesive layer 16 and the first copper-clad laminate 13 are sequentially laminated on the copper foil 112, and the adhesive layer 17 and the second copper-clad laminate 14 are laminated on the second copper foil 122, and then pressed. Hehe. The first copper clad laminate 13 includes an insulating layer 131 and a copper foil 132 formed on the insulating layer 131. The second copper clad laminate 14 includes an insulating layer 141 and a copper foil 142 formed on the insulating layer 141. The insulating layer 131 is adjacent to the adhesive layer 16. The insulating layer 141 is adjacent to the adhesive layer 17. Referring to FIG. 5, via holes 18 are formed to turn on the copper foil 112, the copper foil 122, the copper foil 132, and the copper foil 142. The via hole 18 can be formed by mechanical drilling or laser-bronching. A conductive layer may be placed on the inner wall of the via hole 18, such as a layer of copper. Or, the conductive vias are filled in the via holes 18. In this embodiment, the inner wall of the via hole 18 is plated with a copper layer. Referring to Fig. 6, a wiring is formed on the copper foil 132 and the copper foil 142, and a recess 134 is formed on the copper foil 132 at a region corresponding to the side 154 and the recess 114 to obtain a prefabricated circuit board 19. The recess 134 may be formed by etching simultaneously with the line, or may be fired by a Nd:YAG laser before or after the line is formed. Referring to FIGS. 7 and 8, the slit 191 is formed by cutting the insulating layer 131, the adhesive layer 16, and the insulating layer 111 by the carbon dioxide laser alignment groove 134 11 1315171. Under normal circumstances, when the carbon dioxide laser is drilled in the insulating layer/adhesive layer, the drilling speed is fast, but the wavelength is different from the wavelength that can be absorbed by the copper foil, so the copper foil 124 cannot be cut by the carbon dioxide laser. Thereby, it can serve as a cut-off layer, and after the insulating layer 111 is cut, the copper foil 124 can prevent the carbon dioxide laser from being further cut downward. Figure 9 is a top plan view of the prefabricated circuit board of Figure 10. The portion of the boundary 192 is the area where the final finished circuit board is located. Referring to Figure 9, the prefabricated circuit board 19 is cut along the boundary 192 to remove portions of the pre-made circuit board 19 from the upper boundary 192. A side surface 194 is formed on the prefabricated circuit board 19 after cutting. Referring to Figures -11, side 194 and slit 191 are collectively disposed on prefabricated circuit board 19 as a removal zone 193. At this time, since the removal region 193 corresponds to the opening 152, the removal region 193 is also disconnected from the prefabricated circuit board 19. The removal region 193 can be detached from the prefabricated circuit board 19 to obtain a flexible circuit board 100 having a stepped structure. When cutting, you can use die punching or tool cutting. In the embodiment, the recess 114 and the recess 134 are respectively formed in the copper foil 112 and the copper foil 132. Therefore, the carbon dioxide laser can smoothly cut the insulating layer 111, the insulating layer 131 and the adhesive layer 16, due to the existence of the cut-off copper foil 124. The carbon dioxide laser can be prevented from further cutting down to damage the circuit board 100. In the present embodiment, a partial circuit is formed in four layers, and the other portion is a two-layer flexible circuit board. However, after the first copper clad laminate 11, the adhesive layer 15 and the second copper clad laminate 12 are pressed and combined to form a line, the first copper clad laminate 11 can be cut by laser to obtain a part of two layers, a part of which is 12 1315171. A flexible circuit board that is an early layer. Alternatively, an additional copper clad laminate may be laminated on the first copper clad laminate i3 and the second copper press plate 4. Other Processes = Similar to the fabrication of the flexible circuit board having the stepped structure of the first embodiment: In the present embodiment, the plates are respectively laminated on both surfaces of the adhesive layer 15 and lines are formed on the copper cases of the copper clad laminate. Alternatively, it is also a laminate of copper clad laminates which have been pre-formed with wires. Other processes An embodiment is similar. & Compared with the prior art, the method for fabricating a flexible circuit board having a faulty surname has the following advantages: First, when the circuit board is formed with a line or a through hole, there is no fault structure on the circuit board. Therefore, it is possible to avoid the occurrence of defects such as peeling of the copper layer and disconnection, and it is possible to improve the yield of the product. Secondly, when the circuit board or the track is on the circuit board, there is no knife edge formed on the circuit board, which avoids the intrusion of the syrup from the knife edge when forming the line or the through hole, resulting in a defective circuit board. Finally, cutting with a laser can result in a more accurate section size. The method of fabricating the flexible circuit board having the stepped structure of the second embodiment is similar to that of the first embodiment, except that referring to FIG. 12, the second copper clad laminate 22 includes an edge layer 221 formed on the insulating layer 221 The upper copper foil = 22 and the cut-off layer 224. A cutoff layer 224 is formed in a portion of the area that is aligned with the side edges 254. The material of the cut-off layer 224 may be selected from a metal such as chromium, copper, aluminum, etc.: when the cut-off layer 224 can be formed on the second insulating layer by electroplating or sputtering, when the cut-off layer 224 is formed, a mask is attached in advance to expose The area of the cut-off layer 224 is shaped and then plated or sputtered. When forming the cutoff 13 1315171 layer? The mask can be removed after 24 hours. Referring to Figure 13, the cut-off layer 224 functions similarly to the copper foil 124 to prevent further damage to the board after the laser has completed the cutting task. By replacing the copper fl 124' with the cut-off layer 224, the board can be made thinner and its flexural resistance is also stronger. The method of fabricating a flexible circuit board having a stepped structure of the third embodiment is similar to that of the second embodiment except that a groove aligned with the side edge 354 is not formed on the copper foil 312 and the copper foil 3%. Referring to FIGS. 14-17, after forming a predetermined number of prefabricated circuit boards, the cutting is performed with two different laser alignment side edges 354, wherein the first laser 381 is used to cut the copper foil 312 and the copper foil 332. The second laser 382 is used to cut the adhesive layer 36, the insulating layer 311, and the insulating layer 331. The first laser is a solid laser such as a Nd:YAG laser, and the second laser is a gas laser such as carbon dioxide = shot. Since the Nd:YAG laser is suitable for cutting copper boxes, but the frequency is different from that of the edge layer 311 or the adhesive 36 material, it is difficult to cut the insulating layer milk or the adhesive layer 36, and the carbon dioxide laser is just the opposite. In summary, the present invention has indeed met the requirements of the invention patent, and is legally qualified. However, the above is only the preferred embodiment of the present invention, and γ cannot limit the scope of patent application in this case. Equivalent modifications or variations made by those who are familiar with the skill of the present invention should be covered in the scope of the following patent application. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 to FIG. 11 are schematic views showing a method of fabricating a flexible 14 1315171 circuit board having a stepped structure according to a first embodiment. Fig.-12 to Fig. 13 are views showing a method of fabricating a flexible circuit board having a stepped structure in the second embodiment. 14 to 17 are views showing a method of fabricating a flexible circuit board having a stepped structure in the third embodiment. 18 to 23 are schematic views showing a method of fabricating a flexible circuit board having a stepped structure in the prior art. [Description of main component symbols] 111,211,121,221,131,331,141 112,212,312,122,222,132,332,142,124 15,25,16,36,17 154,254,354 114,134 via hole 18 19 slit 191 192 side 194 224 first laser 381 382 _ first copper clad laminate 11,13,21 second cover Copper laminate 12, 14, 22 * Insulation copper pig adhesive layer side groove φ prefabricated circuit board boundary cutoff layer second laser 15