[關於銅箔] 本發明之雙面電路用基板所使用之銅箔較佳為與氟樹脂接觸之面之二維粗糙度(Ra)處於0.2 μm以下之範圍內，更佳為處於0.15 μm以下之範圍內。若二維粗糙度Ra超過0.2 μm，則有傳輸損耗變大，不滿足雙面電路用基板之實用性能之情況。作為通常之銅箔之種類，可列舉電解箔與壓延箔，於本發明之雙面電路用基板可使用任一種銅箔。銅箔之厚度較佳為5至50 μm，更佳為8至40 μm。 銅箔之與氟樹脂接觸之面可未經處理，亦可實施表面處理。作為表面處理之具體例，例如可列舉利用選自鎳、鐵、鋅、金、銀、鋁、鉻、鈦、鈀或錫中之1種以上之金屬進行之鍍覆處理，較佳為利用選自鎳、鐵、鋅、金或鋁中之1種以上之鍍覆處理，更佳為利用鎳或鋁之鍍覆處理，較佳為視情況選自鎳、鐵、鋅、金或錫中之1種以上之金屬鍍覆處理。又，亦可對未經處理之銅箔表面或利用上述金屬進行過鍍覆處理之銅箔表面，利用矽烷偶合劑等藥劑實施表面改質。 [關於玻璃不織布] 本發明之雙面電路用基板所使用之玻璃不織布並無特別限定，例如可列舉利用少量黏合劑化合物(樹脂或無機物)固著有玻璃之短纖維者，或者不使用黏合劑化合物，藉由使玻璃短纖維纏繞而維持其形狀者，可使用該等之市售品。 構成玻璃不織布之玻璃短纖維之直徑較佳為0.5至30 μm，纖維長較佳為5至30 mm。作為用於玻璃不織布之黏合劑化合物之具體例，可列舉：環氧樹脂、丙烯酸樹脂、纖維素、聚乙烯醇、氟樹脂等樹脂，或二氧化矽化合物等無機物。黏合劑化合物之使用量相對於玻璃短纖維通常為3～15質量%。作為玻璃短纖維之材質，可列舉E玻璃、C玻璃、A玻璃、S玻璃、D玻璃、NE玻璃、低介電常數玻璃等。 玻璃不織布之厚度通常為50 μm至1000 μm，較佳為100 μm至900 μm。再者，所謂本說明書中之「玻璃不織布之厚度」，係指依據JIS P8118：1998，使用小野測器股份有限公司製造之數位規DG-925(荷重110克，面徑10 mm)對玻璃不織布測得之值。為提高玻璃不織布與氟樹脂之親和性，亦可對玻璃不織布實施矽烷偶合劑處理。 玻璃不織布通常空隙率非常高，為80%以上，作為材料，使用厚於下述包含氟樹脂之膜者，較佳為藉由熱板壓時之壓力進行壓縮而使用。通常，玻璃不織布係以其本來之厚度於空隙含浸樹脂而使用，但於本發明中，與更薄之膜併用，較本來之厚度大幅地進行壓縮，藉此玻璃纖維遍及基板之整個厚度方向，可不增加彈性模數而使Z軸方向之線膨脹率明顯降低。 [關於氟樹脂] 本發明中使用之氟樹脂並無特別限定，例如較佳為選自由聚四氟乙烯[PTFE]、聚氯三氟乙烯[PCTFE]、乙烯-TFE共聚物[ETFE]、乙烯-氯三氟乙烯[ECTFE]共聚物、CTFE-TFE共聚物、四氟乙烯-六氟丙烯共聚物[TFE-HFP共聚物、FEP]、四氟乙烯-全氟烷基乙烯基醚共聚物[TFE-PAVE共聚物、PFA]、及聚偏二氟乙烯[PVdF]所組成之群中之至少1種，就電氣特性(介電常數、介電損耗正切)或耐熱性等觀點而言，更佳為PFA及/或FEP，進而較佳為PFA。再者，氟樹脂可於不阻礙本發明之效果之範圍內，包含氟樹脂以外之成分。 上述PFA係包含基於TFE之聚合單元(TFE單元)、及基於PAVE之聚合單元(PAVE單元)之共聚物。 於PFA中，PAVE並無特別限定，例如可列舉下述通式(1)： CF2
=CF-ORf1
(1) 所表示之全氟不飽和化合物。式中，Rf1
表示全氟有機基。 再者，於本說明書中，所謂「全氟有機基」，係意指與碳原子鍵結之氫原子全部被取代為氟原子之有機基，全氟有機基亦可具有醚鍵結性之氧原子。 作為上述PAVE，較佳為於上述通式(1)中，Rf1
為碳數1至10之全氟烷基者，更佳為碳數為1至5之全氟烷基者。 作為上述PAVE，更佳為選自由全氟(甲基乙烯基醚)[PMVE]、全氟(乙基乙烯基醚)[PEVE]、全氟(丙基乙烯基醚)[PPVE]、及全氟(丁基乙烯基醚)所組成之群中之至少1種，進而較佳為選自由PMVE、PEVE及PPVE所組成之群中之至少1種，於耐熱性優異之方面，尤佳為PPVE。 上述PFA較佳為PAVE單元為1至10莫耳%者，更佳為3至6莫耳%者。又，上述PFA較佳為相對於全部聚合單元，TFE單元及PAVE單元合計為90至100莫耳%。 上述PFA亦可為包含TFE單元、PAVE單元、以及基於可與TFE及PAVE共聚合之單體之聚合單元的共聚物。作為可與TFE及PAVE共聚合之單體，較佳為選自由六氟丙烯、CX1
X2
=CX3
(CF2
)nX4
(式中，X1
、X2
及X3
可相同亦可不同，表示氫原子或氟原子。X4
表示氫原子、氟原子或氯原子。n表示2至10之整數)所表示之乙烯系單體、CF2
=CF-OCH2
-Rf2
(式中，Rf2
表示碳數1至5之全氟烷基)所表示之烷基全氟乙烯基醚衍生物所組成之群中之至少1種。 作為上述烷基全氟乙烯基醚衍生物，較佳為Rf2
為碳數1至3之全氟烷基者，更佳為CF2
=CF-OCH2
-CF2
CF3
。 於PFA具有基於可與TFE及PAVE共聚合之單體之聚合單元之情形時，PFA較佳為源自可與TFE及PAVE共聚合之其他單體之單體單元為0至10莫耳%，TFE單元及PAVE單元合計為90至100莫耳%。更佳為源自可與TFE及PAVE共聚合之其他單體之單體單元為0.1至10莫耳%，TFE單元及PAVE單元合計為90至99.9莫耳%。 FEP係包含基於四氟乙烯之聚合單元(TFE單元)、及基於六氟丙烯之聚合單元(HFP單元)之共聚物。 作為FEP，並無特別限定，較佳為TFE單元與HFP單元之莫耳比(TFE單元/HFP單元)為70至99/30至1之共聚物，更佳為80至97/20至3之共聚物。若TFE單元過少，則有機械物性降低之傾向，若過多，則有熔點變得過高，成形性降低之傾向。 FEP亦較佳為源自可與TFE及HFP共聚合之其他單體之單體單元為0.1至10莫耳%，TFE單元及HFP單元合計為90至99.9莫耳%之共聚物。作為可與TFE及HFP共聚合之其他單體，可列舉PAVE、烷基全氟乙烯基醚衍生物等。 上述共聚物之各單體之含量可藉由根據單體之種類，適當組合NMR(nuclear magnetic resonance，核磁共振)、FT-IR(fourier transform infrared radiation，傅立葉轉換紅外線光譜)、元素分析、螢光X射線分析而算出。 上述氟樹脂之熔體流動速率(MFR)較佳為1.0 g/10分鐘以上，更佳為2.5 g/10分鐘以上，進而較佳為10 g/10分鐘以上。MFR之上限例如為100 g/10分鐘。 上述MFR係依據ASTM D3307，於溫度372℃、荷重5.0 kg之條件下進行測定而獲得之值。 氟樹脂之熔點較佳為320℃以下，更佳為310℃以下。若鑒於耐熱性及雙面基板之製作中之加工性，則熔點較佳為260℃以上，更佳為265℃以上。 上述熔點係使用DSC(示差掃描熱量測定)裝置，以10℃/分鐘之速度升溫時之熔解峰所對應之溫度。 於以膜形態使用氟樹脂之材料之情形時，該膜可藉由利用熔融擠出成形法、溶劑澆鑄法或噴霧法等公知之方法，使上述能夠進行熔融加工之氟樹脂或包含該氟樹脂之組合物成形而獲得。包含氟樹脂之1片膜之厚度較佳為10至100 μm，更佳為20至80 μm。 作為本發明之雙面電路用基板所使用之包含氟樹脂及玻璃不織布之複合材料，可使用正面及背面經氟樹脂被覆之玻璃不織布。作為自氟樹脂與玻璃不織布獲得複合材料之方法，例如可列舉： I.將預先成形並經過表面處理之氟樹脂之膜與玻璃不織布於加熱下進行壓接之方法； II.使自模具等擠出之氟樹脂之熔融物與玻璃不織布於加熱下進行複合化及成形之方法； 等，於考慮生產性之情形時，較佳為方法I。 於上述方法I中，於在加熱下進行壓接(熱壓接)之情形時，通常可於250～400℃之範圍內，以0.1～10兆帕斯卡之壓力進行1～20分鐘。關於熱壓接溫度，若變為高溫，則有產生樹脂之滲出、或厚度之不均勻化之擔憂，較佳為未達350℃，更佳為340℃以下。熱壓接可使用加壓機批次式地進行，又，亦可使用高溫貼合機連續地進行。於使用加壓機之情形時，為防止空氣之夾入，提高氟樹脂於玻璃不織布內之含浸性，較佳為使用真空加壓機。再者，於氟樹脂於玻璃不織布中之含浸性較低之情形時，於形成通孔時，容易產生鍍覆液滲透至玻璃布內，於通孔間出現短路之問題，因此必須注意。但是，於本說明書中，無論包含氟樹脂之膜對玻璃不織布是否充分地含浸，均將由氟樹脂膜及玻璃不織布構成之交替層設為複合材料之一形態。 其特徵在於：本發明之雙面電路用基板所使用之複合材料之表面或包含氟樹脂之膜之表面(任一情形時之表面均為與銅箔接觸之表面)利用ESCA觀察到之氧原子之存在比率為1.0%以上。與銅箔接觸之表面之利用ESCA觀察到之氧原子之存在比率較佳為1.2%以上，更佳為1.8%以上，進而較佳為2.5%以上。關於上限，並無特別限定，若鑒於對生產性或其他物性之影響，則較佳為15%以下。與銅箔接觸之表面之利用ESCA觀察到之氮原子之存在比率並無特別限定，較佳為0.1%以上。 為了將與銅箔接觸之表面之利用ESCA觀察到之氧原子之存在比率設為1.0%以上，可對複合材料之表面(複合材料之氟樹脂之表面)及包含氟樹脂之膜之表面進行改質。再者，於複合材料之情形時，亦可藉由上述方法，將預先經表面改質之包含氟樹脂之膜與玻璃不織布壓接，而獲得表面經改質之複合材料。 表面改質可採用先前公知之電暈放電處理或輝光放電處理、電漿放電處理、利用濺鍍處理等進行之放電處理。例如除可藉由於放電環境中導入氧氣、氮氣、氫氣等控制表面自由能以外，可將應改質之表面置於包含有機化合物之惰性氣體(例如氮氣、氦氣、氬氣等)環境中，藉由於電極間施加高頻電壓而產生放電，藉此於表面生成活性種，繼而導入有機化合物之官能基或者使聚合性有機化合物接枝聚合，藉此進行表面改質。 作為此處使用之有機化合物，係含有氧原子之聚合性或非聚合性有機化合物，例如可列舉：乙酸乙烯酯、甲酸乙烯酯等乙烯酯類；甲基丙烯酸縮水甘油酯等丙烯酸酯類；乙烯基乙醚、乙烯基甲醚、縮水甘油基甲醚等醚類；乙酸、甲酸等羧酸類；甲醇、乙醇、苯酚、乙二醇等醇類；丙酮、甲基乙基酮等酮類；乙酸乙酯、甲酸乙酯等羧酸酯類；丙烯酸、甲基丙烯酸等丙烯酸類等。該等之中，就經改質之表面不易失活(壽命長)之方面、於安全性方面容易處理之方面而言，較佳為乙烯酯類、丙烯酸酯類、酮類，尤佳為乙酸乙烯酯、甲基丙烯酸縮水甘油酯。 用於表面改質之有機化合物之濃度根據該表面改質之氟樹脂或有機化合物之種類等而異，通常為0.1至3.0容量%，較佳為0.1至1.0容量%。放電條件只要根據目標之表面改質之程度、氟樹脂之種類、有機化合物之種類或濃度等進行適當選定即可，通常於荷電密度為0.3至9.0 W・sec/cm2
、較佳為0.3至3.0 W・sec/cm2
之範圍內進行放電處理。處理溫度可以0至100℃之範圍之任意溫度進行。 [適於雙面電路之基板之製作方法] 繼而，對製作本發明之適於雙面電路之基板之方法進行說明。 作為獲得本發明之適於雙面電路之基板之方法，例如可列舉如下方法等： A法：將兩片銅箔與上述複合材料，以二維粗糙度Ra為0.2 μm以下之銅箔面與複合材料相對向之方式，依序將銅箔-複合材料-銅箔重疊而形成積層體後，於加熱下進行壓接； B法：將n片包含氟樹脂之膜及n－1片玻璃不織布交替重疊而獲得包含氟樹脂之膜與玻璃不織布之交替層之後，於該積層體之最上層之包含氟樹脂之膜上方及最下層之包含氟樹脂之膜下方，以二維粗糙度Ra為0.2 μm以下之銅箔面與包含氟樹脂之膜相對向之方式分別設置銅箔，形成積層體後，於加熱下進行壓接。 上述A法係使用一片複合材料之最簡單之製備方法，亦可於兩片銅箔之間使用複數片複合材料而製備雙面電路用基板。於使用複數片複合材料之情形時，只要複合材料之與銅箔接觸之面(氟樹脂之表面)之利用ESCA觀察到之氧原子之存在比率為1.0%以上，則與其他複合材料接觸之面之利用ESCA觀察到之氧原子之存在比率亦可未達1.0%。 再者，上述A法係僅雙面設置有銅箔之雙面電路基板之製備方法，但使用三片以上之銅箔而獲得之三層以上之多層基板，或於雙面具有銅箔之雙層基板之銅箔上進而積層有氟樹脂層(及玻璃不織布)之構成之電路用基板亦包含於本發明之雙面電路用基板之範疇。 若更具體地說明上述B法，則例如於使用兩片包含氟樹脂之膜及一片玻璃不織布而製備雙面電路用基板之情形時，係以銅箔之二維粗糙度Ra為0.2 μm以下之面與包含氟樹脂之膜之利用ESCA觀察到之氧原子之存在比率為1.0%以上之面相對向之方式，依序將銅箔-包含氟樹脂之膜-玻璃不織布-包含氟樹脂之膜-銅箔重疊後，於加熱下進行壓接之方法。於該情形時，氟樹脂膜之與玻璃不織布相對向之面之利用ESCA觀察到之氧原子之存在比率亦可未達1.0%。又，例如於使用三片包含氟樹脂之膜及兩片玻璃不織布而製備雙面電路用基板之情形時，係以銅箔之二維粗糙度Ra為0.2 μm以下之面與包含氟樹脂之膜之利用ESCA觀察到之氧原子之存在比率為1.0%以上之面相對向之方式，依序將銅箔-包含氟樹脂之膜-玻璃不織布-包含氟樹脂之膜-玻璃不織布-包含氟樹脂之膜-銅箔重疊後，於加熱下進行壓接之方法。 再者，上述B法係於雙面設置有銅箔之雙面電路基板之製備方法，但於雙面具有銅箔之雙層基板之銅箔上進而積層有氟樹脂層(及玻璃不織布)之電路用基板、或介隔n片包含氟樹脂之膜及n－1片玻璃不織布而積層銅箔之構成之多層基板亦包含於本發明之雙面電路用基板之範疇。 上述A法及B法中之熱壓接只要利用依據獲得複合材料之方法之部分中記載之熱壓接之各條件之方法進行即可。 上述經過表面處理之包含氟樹脂之膜單獨無法對二維粗糙度Ra為0.2 μm以下之銅箔具有充分之接著強度，於熱壓接時自銅箔滲出，無法實現厚度之均勻化，但藉由併用玻璃不織布，或者藉由製成與玻璃不織布之複合材料，而使Z軸方向之線膨脹率充分降低，進而樹脂之滲出亦減少，對二維粗糙度Ra為0.2 μm以下之銅箔亦表現出較高之接著性。 本發明之雙面電路用基板所使用之包含氟樹脂之膜之片數n通常為2至10之整數，較佳為2至8之整數，更佳為2至6之整數。藉由改變氟樹脂膜之厚度或玻璃不織布之種類或厚度、及n之值，可改變本發明之介電層之XY方向之線膨脹率，但線膨脹率之值較佳為5至50 ppm/℃之範圍內，更佳為10至40 ppm/℃之範圍內。若介電層之線膨脹率超過50 ppm/℃，則銅箔與介電層之密接性變低，又，於銅箔蝕刻後，變得容易產生基板之翹曲或表面波紋等異常。 自本發明之雙面電路用基板去除銅箔而得之絕緣體層之彈性模數於常溫下較佳為5 GPa以下，更佳為4 GPa以下。於高頻基板中，為防止介電特性變差，多數情況為於半導體晶片與基板之間不添加作為應力緩和劑之底部填充膠，但於此種情形時，若基板之彈性模數超過5 GPa，則無法充分緩和於基板上產生之應力，對半導體晶片造成損傷之可能性較高。 自本發明之雙面電路用基板去除銅箔而得之絕緣體層中之玻璃不織布之含量通常為10至90質量%，較佳為15至85質量%。 於本發明中，所謂高頻電路，不僅為包含僅傳輸高頻信號之電路者，而且亦包含將高頻信號轉換為低頻信號並將所產生之低頻信號向外部輸出之傳輸路徑、或用以供給供於高頻對應零件之驅動之電源之傳輸路徑等傳輸非高頻信號之信號之傳輸路徑亦並設於同一平面上之電路。 [實施例] 以下基於實施例及比較例更具體地說明本發明，但本發明並不限定於以下之實施例。再者，實施例中之測定及評價係利用以下記載之裝置及方法進行。再者，所謂絕緣體層，係指雙面電路用基板之銅箔以外之部分之層。 (銅箔表面之二維粗糙度Ra) 使用小阪研究所股份有限公司製造之SE-500，利用觸針法進行測定。 (氟樹脂表面之ESCA分析) 藉由X射線光電子光譜裝置(島津製作所股份有限公司製造之ESCA-750)進行測定。 (銅箔之剝離強度(接著強度)) 依據JIS C5016-1994，一面以每分鐘50 mm之速度，於相對於銅箔去除面為90度之方向上剝離銅箔，一面藉由拉伸試驗機，測定銅箔之剝離強度(於本說明書中亦稱為銅箔之剝離(peel)強度)。 (絕緣體層之彈性模數) 對所製作之雙面基板之銅箔進行蝕刻之後，藉由拉伸試驗機(島津製作所股份有限公司製造之AGS-X)進行測定。 (雙面電路用基板之介電常數、介電損耗正切) 對所製作之雙面基板之銅箔進行蝕刻之後，藉由空腔共振器(關東電子應用開發股份有限公司製造)以1 GHz進行測定，並利用網路分析儀(Agilent Technology股份有限公司製造，型號8719ET)進行分析。 (雙面電路用基板之傳輸損耗) 藉由蝕刻，製作長度10 cm之微帶線，並使用網路分析儀對40 GHz下之傳輸損耗進行測定。 (絕緣體層之Z軸方向之線膨脹率) 藉由雷射熱膨脹計(LIX-2M；ADVANCE RIKO股份有限公司製造)進行測定。 實施例1 準備二維粗糙度Ra為0.08 μm之厚度18 μm之未粗化處理電解銅箔(福田金屬箔粉工業股份有限公司製造 製品名CF-T9DA-SV-18)2片、厚度50 μm之對兩面進行表面處理(於電暈放電裝置之放電電極與輥狀接地電極之附近流通包含乙酸乙烯酯0.13體積%之氮氣，並且使膜沿著輥狀接地電極連續地通過，以荷電密度1.7 w・s/cm2
對膜之兩面進行電暈放電處理)且利用ESCA表面分析所得之氧原子之存在比率為2.62%的四氟乙烯-全氟烷基乙烯基醚共聚物(PFA)膜(TFE/PPVE＝98.5/1.5(莫耳%)，MFR：14.8 g/10分鐘，熔點：305℃)2片、及厚度423 μm之玻璃不織布(Oribest股份有限公司製造之SYS053)1片，使銅箔之無光澤面(二維粗糙度Ra為0.08 μm)成為內側(即，以無光澤面與PFA膜接觸之方式配置)，以銅箔/PFA膜/玻璃不織布/PFA膜/銅箔之順序進行積層。使用真空加壓機於325℃下對該積層體進行30分鐘熱壓，藉此製作厚度為125 μm之本發明之雙面電路用基板1。 實施例2 於實施例1中，將2片PFA膜之厚度一片設為50 μm，另一片設為25 μm，其後藉由與實施例1相同之方式，製作厚度為100 μm之本發明之雙面電路用基板2。 實施例3 於實施例1中，將2片PFA膜均變更為FEP膜，使用與實施例1相同之進行過雙面處理者，除此以外，藉由相同方式，製作厚度為125 μm之雙面電路用基板3。 比較例1 於實施例1中，代替玻璃不織布而替換為厚度為43 μm之玻璃布(Arisawa製作所股份有限公司製造之IPC型號1078)，除此以外，藉由相同之方式，製作厚度為120 μm之雙面電路用基板4。 使用上述雙面電路用基板1、2、3、4，對銅箔與氟樹脂之間之剝離強度進行測定。又，對銅箔進行蝕刻，測定絕緣體層之彈性模數、介電常數、介電損耗正切及Z軸方向之線膨脹率。進而製作微帶線，測定40 GHz下之傳輸損耗。 [表1]
可知：根據實施例，可容易地製造線膨脹率較小，銅箔剝離強度(銅箔剝離強度)較強，而且高頻下之傳輸損耗較少之雙面電路用基板。可知與使用不同之玻璃材料(玻璃布)之比較例相比，尤其是使用玻璃不織布之實施例可將Z軸方向之線膨脹率抑制為更低。因此，本發明之雙面電路用基板於工業上極有用。[About copper foil] The copper foil used for the double-sided circuit board of the present invention preferably has a two-dimensional roughness (Ra) of a surface in contact with the fluororesin within a range of 0.2 μm or less, and more preferably 0.15 μm or less. Within range. If the two-dimensional roughness Ra exceeds 0.2 μm, the transmission loss may increase, which may not satisfy the practical performance of a substrate for a double-sided circuit. Typical types of copper foil include electrolytic foil and rolled foil, and any type of copper foil can be used for the double-sided circuit substrate of the present invention. The thickness of the copper foil is preferably 5 to 50 μm, and more preferably 8 to 40 μm. The surface of the copper foil in contact with the fluororesin may be left untreated or surface treated. Specific examples of the surface treatment include, for example, a plating treatment using one or more metals selected from the group consisting of nickel, iron, zinc, gold, silver, aluminum, chromium, titanium, palladium, and tin. One or more plating treatments from nickel, iron, zinc, gold, or aluminum, more preferably a nickel or aluminum plating treatment, preferably selected from nickel, iron, zinc, gold, or tin, as appropriate One or more types of metal plating. In addition, the surface of the untreated copper foil or the surface of the copper foil that has been plated with the above-mentioned metal may be surface-modified using a silane coupling agent or the like. [About glass non-woven fabric] The glass non-woven fabric used for the double-sided circuit board of the present invention is not particularly limited, and examples thereof include those in which a short fiber with glass is fixed by a small amount of an adhesive compound (resin or inorganic substance), or an adhesive is not used. As the compound, a commercially-available product can be used as long as the short glass fiber is wound to maintain its shape. The diameter of the short glass fibers constituting the glass nonwoven fabric is preferably 0.5 to 30 μm, and the fiber length is preferably 5 to 30 mm. Specific examples of the adhesive compound used for the glass nonwoven fabric include resins such as epoxy resin, acrylic resin, cellulose, polyvinyl alcohol, and fluororesin, and inorganic substances such as silicon dioxide compounds. The usage-amount of a binder compound is normally 3-15 mass% with respect to a glass short fiber. Examples of the material of the short glass fiber include E glass, C glass, A glass, S glass, D glass, NE glass, and low dielectric constant glass. The thickness of the glass nonwoven fabric is usually 50 μm to 1000 μm, and preferably 100 μm to 900 μm. The "thickness of glass non-woven fabric" in this specification refers to glass non-woven fabric based on JIS P8118: 1998, using a digital gauge DG-925 (load 110 g, face diameter 10 mm) manufactured by Ono Sokoku Co., Ltd. Measured value. In order to improve the affinity between the glass nonwoven fabric and the fluororesin, the glass nonwoven fabric may also be treated with a silane coupling agent. The glass non-woven fabric usually has a very high porosity of 80% or more. As a material, a film containing a fluororesin thicker than the following is used, and it is preferably used by being compressed by the pressure during hot plate pressing. Generally, glass non-woven fabrics are used by impregnating the resin with its original thickness, but in the present invention, it is used in combination with a thinner film to compress it more than its original thickness, so that the glass fiber extends throughout the entire thickness direction of the substrate. The linear expansion rate in the Z-axis direction can be significantly reduced without increasing the elastic modulus. [About fluororesin] The fluororesin used in the present invention is not particularly limited. For example, it is preferably selected from polytetrafluoroethylene [PTFE], polychlorotrifluoroethylene [PCTFE], ethylene-TFE copolymer [ETFE], and ethylene. -Chlorotrifluoroethylene [ECTFE] copolymer, CTFE-TFE copolymer, tetrafluoroethylene-hexafluoropropylene copolymer [TFE-HFP copolymer, FEP], tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer [ At least one of the group consisting of TFE-PAVE copolymer, PFA], and polyvinylidene fluoride [PVdF], from the viewpoint of electrical characteristics (dielectric constant, dielectric loss tangent), or heat resistance, more It is preferably PFA and / or FEP, and further preferably PFA. The fluororesin may contain components other than the fluororesin within a range that does not inhibit the effect of the present invention. The PFA is a copolymer including a TFE-based polymerization unit (TFE unit) and a PAVE-based polymerization unit (PAVE unit). In PFA, PAVE is not particularly limited, and examples thereof include the following general formula (1): CF 2 = CF-ORf 1 (1) A perfluorinated unsaturated compound. In the formula, Rf 1 represents a perfluoroorganic group. In addition, in the present specification, the so-called "perfluoroorganic group" means an organic group in which all hydrogen atoms bonded to carbon atoms have been replaced with fluorine atoms, and the perfluoroorganic group may also have ether-bonding oxygen. atom. As the PAVE, in the general formula (1), Rf 1 is preferably a perfluoroalkyl group having 1 to 10 carbon atoms, and more preferably a perfluoroalkyl group having 1 to 5 carbon atoms. The PAVE is more preferably selected from the group consisting of perfluoro (methyl vinyl ether) [PMVE], perfluoro (ethyl vinyl ether) [PEVE], perfluoro (propyl vinyl ether) [PPVE], and all At least one of the group consisting of fluorine (butyl vinyl ether), and more preferably at least one member selected from the group consisting of PMVE, PEVE, and PPVE. In terms of excellent heat resistance, PPVE is particularly preferred . The PFA is preferably a PAVE unit with 1 to 10 mole%, and more preferably 3 to 6 mole%. In addition, the PFA is preferably 90 to 100 mol% in total of the TFE unit and the PAVE unit with respect to all the polymerization units. The PFA may be a copolymer including a TFE unit, a PAVE unit, and a polymerization unit based on a monomer copolymerizable with TFE and PAVE. As a monomer copolymerizable with TFE and PAVE, it is preferably selected from the group consisting of hexafluoropropylene, CX 1 X 2 = CX 3 (CF 2 ) nX 4 (where X 1 , X 2 and X 3 may be the same or Different, it represents a hydrogen atom or a fluorine atom. X 4 represents a hydrogen atom, a fluorine atom or a chlorine atom. N represents an integer of 2 to 10) an ethylene-based monomer represented by CF 2 = CF-OCH 2 -Rf 2 (where Rf 2 represents at least one member of the group consisting of alkyl perfluoro vinyl ether derivatives represented by a perfluoroalkyl group having 1 to 5 carbon atoms. As the alkyl perfluorovinyl ether derivative, Rf 2 is preferably a perfluoroalkyl group having 1 to 3 carbon atoms, and more preferably CF 2 = CF-OCH 2 -CF 2 CF 3 . In the case where the PFA has a polymerization unit based on a monomer copolymerizable with TFE and PAVE, the PFA preferably has a monomer unit derived from other monomers copolymerizable with TFE and PAVE of 0 to 10 mol%, The total TFE unit and PAVE unit are 90 to 100 mole%. More preferably, the monomer units derived from other monomers copolymerizable with TFE and PAVE are 0.1 to 10 mol%, and the total of TFE units and PAVE units is 90 to 99.9 mol%. FEP is a copolymer containing polymerized units (TFE units) based on tetrafluoroethylene and polymerized units (HFP units) based on hexafluoropropylene. The FEP is not particularly limited, but a copolymer having a molar ratio of TFE unit and HFP unit (TFE unit / HFP unit) of 70 to 99/30 to 1 is preferable, and 80 to 97/20 to 3 is more preferable. Copolymer. If the number of TFE units is too small, the mechanical properties tend to decrease. If the number of TFE units is too large, the melting point becomes too high, and the moldability tends to decrease. The FEP is also preferably a copolymer derived from other monomers copolymerizable with TFE and HFP with a monomer unit of 0.1 to 10 mol%, and a total of TFE units and HFP units of 90 to 99.9 mol%. Examples of other monomers copolymerizable with TFE and HFP include PAVE and alkyl perfluorovinyl ether derivatives. The content of each monomer of the above copolymer can be appropriately combined with NMR (nuclear magnetic resonance), FT-IR (fourier transform infrared radiation), elemental analysis, and fluorescence according to the type of the monomer. Calculated by X-ray analysis. The melt flow rate (MFR) of the fluororesin is preferably 1.0 g / 10 minutes or more, more preferably 2.5 g / 10 minutes or more, and even more preferably 10 g / 10 minutes or more. The upper limit of the MFR is, for example, 100 g / 10 minutes. The MFR is a value obtained by measuring at a temperature of 372 ° C and a load of 5.0 kg in accordance with ASTM D3307. The melting point of the fluororesin is preferably 320 ° C or lower, and more preferably 310 ° C or lower. In view of heat resistance and processability in manufacturing a double-sided substrate, the melting point is preferably 260 ° C or higher, and more preferably 265 ° C or higher. The melting point is the temperature corresponding to the melting peak when a DSC (differential scanning calorimetry) device is used to increase the temperature at a rate of 10 ° C / minute. When a fluororesin material is used in the form of a film, the film can be melt-processed fluororesin or contain the fluororesin by a known method such as a melt extrusion molding method, a solvent casting method, or a spray method. The composition is obtained by molding. The thickness of one film containing a fluororesin is preferably 10 to 100 μm, and more preferably 20 to 80 μm. As the composite material containing a fluororesin and a glass non-woven fabric used in the substrate for a double-sided circuit of the present invention, a glass non-woven fabric coated with a fluororesin on the front and back surfaces can be used. As a method for obtaining a composite material from a fluororesin and a glass non-woven fabric, for example: I. a method in which a film of a fluororesin formed in advance and surface-treated and a glass non-woven fabric are pressure-bonded under heating; II. Extruding from a mold or the like The method of compounding and forming the molten material of the fluororesin and the glass nonwoven fabric under heating; etc. In consideration of productivity, method I is preferred. In the above method I, in the case of performing compression bonding (thermocompression bonding) under heating, it is usually performed at a pressure of 0.1 to 10 MPa in a range of 250 to 400 ° C for 1 to 20 minutes. Regarding the thermocompression bonding temperature, if the temperature becomes high, bleeding of the resin or uneven thickness may be caused. The temperature is preferably less than 350 ° C, and more preferably 340 ° C or less. The thermocompression bonding may be performed batchwise using a press, or may be performed continuously using a high-temperature bonding machine. In the case of using a press, in order to prevent air from being trapped and improve the impregnation of the fluororesin in the glass nonwoven fabric, it is preferable to use a vacuum press. Furthermore, when the impregnability of the fluororesin in the glass non-woven fabric is low, when the through holes are formed, it is easy for the plating solution to penetrate into the glass cloth and short-circuit problems occur between the through holes. Therefore, attention must be paid. However, in this specification, regardless of whether the glass non-woven fabric is sufficiently impregnated with the film containing a fluororesin, the alternating layer composed of the fluororesin film and the glass non-woven fabric is made into a composite material. It is characterized in that the surface of the composite material used for the substrate for a double-sided circuit of the present invention or the surface of a film containing a fluororesin (the surface in any case is the surface in contact with the copper foil), oxygen atoms observed by ESCA The existence ratio is 1.0% or more. The presence ratio of oxygen atoms observed by ESCA on the surface in contact with the copper foil is preferably 1.2% or more, more preferably 1.8% or more, and even more preferably 2.5% or more. The upper limit is not particularly limited, and it is preferably 15% or less in view of the influence on productivity or other physical properties. The presence ratio of nitrogen atoms observed on the surface in contact with the copper foil by ESCA is not particularly limited, but is preferably 0.1% or more. In order to set the presence ratio of oxygen atoms observed by ESCA on the surface in contact with the copper foil to 1.0% or more, the surface of the composite material (the surface of the fluororesin of the composite material) and the surface of the film containing the fluororesin can be modified. quality. Furthermore, in the case of a composite material, the surface-modified composite material can also be obtained by crimping a film containing a fluororesin that has been surface-modified in advance with a glass nonwoven fabric by the method described above. The surface modification may use a conventionally known corona discharge treatment or glow discharge treatment, a plasma discharge treatment, or a discharge treatment using a sputtering treatment or the like. For example, in addition to controlling the free energy of the surface by introducing oxygen, nitrogen, hydrogen, etc. into the discharge environment, the surface to be modified can be placed in an environment of an inert gas (such as nitrogen, helium, argon, etc.) containing organic compounds, A discharge is generated by applying a high-frequency voltage between the electrodes, thereby generating an active species on the surface, and then introducing a functional group of an organic compound or graft polymerizing a polymerizable organic compound to perform surface modification. The organic compound used herein is a polymerizable or non-polymerizable organic compound containing an oxygen atom, and examples thereof include vinyl esters such as vinyl acetate and vinyl formate; acrylic esters such as glycidyl methacrylate; ethylene Ethers such as methyl ether, vinyl methyl ether and glycidyl methyl ether; carboxylic acids such as acetic acid and formic acid; alcohols such as methanol, ethanol, phenol, and ethylene glycol; ketones such as acetone and methyl ethyl ketone; ethyl acetate Carboxylic esters such as esters and ethyl formate; acrylics such as acrylic acid and methacrylic acid. Among these, vinyl esters, acrylates, and ketones are preferred from the viewpoint that the modified surface is less prone to deactivation (long life) and the safety is easy to handle, and acetic acid is particularly preferred. Vinyl ester, glycidyl methacrylate. The concentration of the organic compound used for surface modification varies depending on the type of the surface-modified fluororesin or organic compound, etc., and is usually 0.1 to 3.0% by volume, and preferably 0.1 to 1.0% by volume. The discharge conditions may be appropriately selected depending on the degree of surface modification of the target, the type of fluororesin, the type or concentration of organic compounds, etc., and the charge density is usually 0.3 to 9.0 W · sec / cm 2 , preferably 0.3 to Discharge treatment was performed in a range of 3.0 W · sec / cm 2 . The treatment temperature may be performed at any temperature ranging from 0 to 100 ° C. [Manufacturing method of a substrate suitable for a double-sided circuit] Next, a method of manufacturing a substrate suitable for a double-sided circuit of the present invention will be described. As a method for obtaining a substrate suitable for a double-sided circuit of the present invention, for example, the following methods can be cited: Method A: Two pieces of copper foil and the above-mentioned composite material are formed with a copper foil surface with a two-dimensional roughness Ra of 0.2 μm or less. In a way that the composite materials face each other, copper foil-composite material-copper foil are sequentially stacked to form a laminate, and then pressure-bonded under heating; Method B: n sheets of fluororesin film and n-1 sheets of glass nonwoven fabric After alternately overlapping to obtain an alternating layer of a film containing fluororesin and a glass non-woven fabric, the two-dimensional roughness Ra is 0.2 above the uppermost layer of the fluororesin-containing film and the lowermost layer of the fluororesin-containing film of the laminate. A copper foil with a thickness of μm or less is provided with a copper foil so as to face the film containing a fluororesin, and after forming a laminated body, pressure bonding is performed under heating. The above method A is the simplest preparation method using one sheet of composite material, and a plurality of sheets of composite material can also be used between two copper foils to prepare a substrate for a double-sided circuit. In the case of using a plurality of composite materials, as long as the surface of the composite material in contact with the copper foil (the surface of the fluororesin) has an oxygen atom presence ratio of 1.0% or more observed by ESCA, the surface in contact with other composite materials The presence of oxygen atoms observed by ESCA may not reach 1.0%. Furthermore, the above-mentioned A method is a method for preparing a double-sided circuit substrate provided with copper foil only on both sides, but using three or more copper foils to obtain a multilayer substrate of three or more layers, or a double-sided substrate having copper foil on both sides The circuit board including a fluororesin layer (and glass nonwoven fabric) laminated on the copper foil of the multi-layer board is also included in the category of the double-sided circuit board of the present invention. To explain the above-mentioned B method more specifically, for example, when two-sided circuit substrates are prepared by using two films containing a fluororesin and one glass non-woven fabric, the two-dimensional roughness Ra of the copper foil is 0.2 μm or less. The copper foil-film containing fluororesin-glass nonwoven fabric-film containing fluororesin- After the copper foils are overlapped, they are crimped under heating. In this case, the presence ratio of oxygen atoms observed by ESCA on the side of the fluororesin film opposite to the glass nonwoven fabric may not reach 1.0%. For example, in the case of using three sheets of fluororesin-containing film and two sheets of glass non-woven fabric to prepare a substrate for a double-sided circuit, the two-dimensional roughness Ra of the copper foil is 0.2 μm or less and the film containing fluororesin. By using ESCA to observe the presence of oxygen atoms with a ratio of 1.0% or more, the copper foil-film containing fluororesin-glass non-woven fabric-film containing fluororesin-glass non-woven fabric-containing fluororesin After the film-copper foil is overlapped, it is a method of pressure bonding under heating. Furthermore, the above-mentioned B method is a method for preparing a double-sided circuit substrate provided with copper foil on both sides, but a fluororesin layer (and glass nonwoven fabric) is laminated on the copper foil of a double-layered substrate with copper foil on both sides Circuit substrates, or multilayer substrates composed of n-sheets containing a fluororesin film and n-1 glass non-woven fabrics laminated with copper foil are also included in the category of double-sided circuit substrates of the present invention. The thermal compression bonding in the above-mentioned methods A and B may be performed by a method according to each condition of the thermal compression bonding described in the section on the method for obtaining a composite material. The above-mentioned surface-treated fluororesin-containing film alone cannot have sufficient bonding strength to a copper foil having a two-dimensional roughness Ra of 0.2 μm or less. It oozes out of the copper foil during thermal compression bonding, and cannot achieve uniform thickness. By using glass non-woven fabric in combination, or by making a composite material with glass non-woven fabric, the linear expansion rate in the Z-axis direction is sufficiently reduced, and the resin exudation is also reduced. The copper foil with a two-dimensional roughness Ra of 0.2 μm or less is also used. Shows higher adhesion. The number n of the fluororesin-containing films used in the substrate for a double-sided circuit of the present invention is usually an integer of 2 to 10, preferably an integer of 2 to 8, and more preferably an integer of 2 to 6. By changing the thickness of the fluororesin film or the type or thickness of the glass nonwoven fabric, and the value of n, the linear expansion ratio in the XY direction of the dielectric layer of the present invention can be changed, but the value of the linear expansion ratio is preferably 5 to 50 ppm In the range of / ° C, more preferably in the range of 10 to 40 ppm / ° C. When the linear expansion rate of the dielectric layer exceeds 50 ppm / ° C, the adhesion between the copper foil and the dielectric layer becomes low, and after the copper foil is etched, it becomes easy to cause substrate warpage or surface ripples and other abnormalities. The elastic modulus of the insulator layer obtained by removing the copper foil from the substrate for a double-sided circuit of the present invention is preferably 5 GPa or less, more preferably 4 GPa or less at room temperature. In high-frequency substrates, in order to prevent deterioration of the dielectric characteristics, in most cases, no underfill as a stress relief agent is added between the semiconductor wafer and the substrate. However, in this case, if the elastic modulus of the substrate exceeds 5 GPa cannot fully alleviate the stress generated on the substrate, and has a high possibility of causing damage to the semiconductor wafer. The content of the glass nonwoven fabric in the insulator layer obtained by removing the copper foil from the substrate for a double-sided circuit of the present invention is usually 10 to 90% by mass, preferably 15 to 85% by mass. In the present invention, the so-called high-frequency circuit includes not only a circuit that transmits only high-frequency signals, but also a transmission path that converts high-frequency signals into low-frequency signals and outputs the generated low-frequency signals to the outside, or Transmission paths for signals transmitting non-high frequency signals, such as a transmission path for a power supply for driving high-frequency corresponding parts, are also circuits arranged on the same plane. [Examples] Hereinafter, the present invention will be described more specifically based on examples and comparative examples, but the present invention is not limited to the following examples. In addition, the measurement and evaluation in an Example were performed using the apparatus and method described below. The insulator layer refers to a layer other than the copper foil of the double-sided circuit board. (Two-dimensional roughness Ra of copper foil surface) Measurement was performed using a stylus method using SE-500 manufactured by Kosaka Research Institute Co., Ltd. (ESCA analysis of fluororesin surface) The measurement was performed with an X-ray photoelectron spectrometer (ESCA-750 manufactured by Shimadzu Corporation). (Peel strength of copper foil (adhesive strength)) According to JIS C5016-1994, the copper foil was peeled at a speed of 50 mm per minute in a direction of 90 degrees with respect to the copper foil removal surface, and a tensile tester was used on the other side. The peel strength of the copper foil (also referred to as the peel strength of the copper foil in this specification) was measured. (Elastic Modulus of Insulator Layer) After the copper foil of the produced double-sided substrate was etched, it was measured with a tensile tester (AGS-X manufactured by Shimadzu Corporation). (Dielectric constant and dielectric loss tangent of the substrate for a double-sided circuit) After etching the copper foil of the produced double-sided substrate, the cavity resonator (manufactured by Kanto Electronics Application Development Co., Ltd.) was used at 1 GHz. The measurement was performed and analyzed using a network analyzer (manufactured by Agilent Technology Co., Ltd., model number 8719ET). (Transmission loss of a substrate for a double-sided circuit) A microstrip line with a length of 10 cm was made by etching, and the transmission loss at 40 GHz was measured using a network analyzer. (Linear expansion coefficient in the Z-axis direction of the insulator layer) The measurement was performed with a laser thermal dilatometer (LIX-2M; manufactured by ADVANCE RIKO Co., Ltd.). Example 1 Two pieces of unroughened electrolytic copper foil with a two-dimensional roughness Ra of 0.08 μm and a thickness of 18 μm (Product name: CF-T9DA-SV-18, manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.) were prepared with a thickness of 50 μm Surface treatment on both sides (Nearly 0.13% by volume of vinyl acetate was passed near the discharge electrode and the roller-shaped ground electrode of the corona discharge device, and the film was continuously passed along the roller-shaped ground electrode with a charge density of 1.7 w · s / cm 2 Corona discharge treatment on both sides of the film) and a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) film with an oxygen atom existence ratio of 2.62% obtained by ESCA surface analysis ( TFE / PPVE = 98.5 / 1.5 (mol%), 2 pieces of MFR: 14.8 g / 10 minutes, melting point: 305 ° C) and 1 piece of glass non-woven cloth (SYS053 manufactured by Oribest Co., Ltd.) with a thickness of 423 μm, made of copper The matte side of the foil (two-dimensional roughness Ra is 0.08 μm) becomes the inner side (that is, arranged in such a way that the matte side is in contact with the PFA film), in the order of copper foil / PFA film / glass non-woven fabric / PFA film / copper foil Laminate. This laminated body was hot-pressed at 325 ° C. for 30 minutes using a vacuum press to produce a double-sided circuit board 1 of the present invention having a thickness of 125 μm. Example 2 In Example 1, the thickness of two PFA films was set to 50 μm, and the other was set to 25 μm. Then, in the same manner as in Example 1, the thickness of the present invention was 100 μm. Double-sided circuit board 2. Example 3 In Example 1, the two PFA films were both changed to FEP films, and the same double-sided treatment as in Example 1 was used. Except for this, a double film having a thickness of 125 μm was produced in the same manner. Surface circuit board 3. Comparative Example 1 In Example 1, a glass cloth (IPC model 1078 manufactured by Arisawa Manufacturing Co., Ltd.) was replaced with a glass cloth having a thickness of 43 μm instead of a glass nonwoven fabric. In the same manner, a thickness of 120 μm was produced. Of the double-sided circuit board 4. The peel strength between the copper foil and the fluororesin was measured using the above-mentioned double-sided circuit substrates 1, 2, 3, and 4. Moreover, the copper foil was etched, and the elastic modulus, the dielectric constant, the dielectric loss tangent, and the linear expansion rate in the Z-axis direction of the insulator layer were measured. Furthermore, a microstrip line was fabricated and the transmission loss at 40 GHz was measured. [Table 1] It is known that according to the embodiment, a substrate for a double-sided circuit with a small linear expansion ratio, a strong copper foil peeling strength (copper foil peeling strength), and a small transmission loss at high frequencies can be easily manufactured. It can be seen that, compared with the comparative example using a different glass material (glass cloth), the embodiment using a glass non-woven fabric can suppress the linear expansion rate in the Z-axis direction to be lower. Therefore, the substrate for a double-sided circuit of the present invention is extremely useful industrially.