1222387 (1) 玖、發明說明 【發明所屬之技術領域】 本發明是關於工作件鑽鑿精密性孔用的鑽頭。 【先前技術】 電子零件等組裝用的印刷配線基板（以下稱印刷基板 )，是把銅箔疊層在強化纖維樹脂上而形成，在該印刷基 板上鑽鑿多數的貫穿孔後，透過電鍍處理使上述貫穿孔的 內壁形成有金屬電鍍層，接著又對該印刷基板表面的銅箔 進行蝕刻處理形成印刷電路，把該印刷電路和下層的銅箔 透過上述金屬電鍍層進行導通電源，接著又將L S I等電 子零件電焊在上述貫穿孔以形成印刷電路板。 然而，近年來，伴隨著電子機器的高性能化、小型化 ，對於印刷電路板要高密度組裝的需求有愈來愈高的趨勢 。根據該需求，在印刷基板之薄板化、高多層化、高密度 配線化前進的同時，加速要鑽鑿在上述印刷基板上之上述 貫穿孔的小徑化的腳步，因此，所使用之鑽頭勢必要小徑 化。 另外，爲了要提昇作業效率和降低製造成本，對於在 印刷基板上的貫穿孔鑽鑿加工，是採複數片重疊該印刷基 板進行貫穿孔鑽鑿加工。因此，貫穿孔的縱橫比（針對孔 直徑之板厚的比）會變大，所以就需愈長的鑽頭。 此外’鑽頭若較長’相對地就需增加鑽頭所需要的強 度。因此，鑽頭就需具有高強度。 •5- (2) (2)1222387 另外，貫穿孔若較深，就愈容易產生孔洞彎曲。因此 ，鑽頭就需具有較高的筆直前進性。 此外’從電的觀點來看，鑽頭當場是要能鑽鑿出良好 的貫穿孔內壁粗糙度，即，鑽頭需能夠鑽鑿出貫穿孔內壁 粗糙度爲盡可能平滑的孔。 整理以上所述，可知對於最近之印刷基板加工用鑽頭 的要求，是其需爲具有鑽徑小，長度長，強度爲高強度， 具優良筆直前進性，並且所鑽鑿出的孔內壁粗糙度爲良好 的鑽頭。 另一方面，第1圖、第2圖爲習知印刷基板之貫穿孔 鑽鑿用的鑽頭3 3 (以下稱習知例）。 該習知例，是於前端設有鑽刃4 1，於外周面設有2 條螺旋狀鑽屑排出溝槽32，於該鑽屑排出溝槽32之間設 有導像部3 1，接著又在鄰接於導像部3 1的位置上設有比 鑽頭33直徑稍小直徑的鏟齒面34，該鏟齒面34之上述 導像部3 1的相反側形成有後跟3 5。此，鑽屑排出溝槽3 2 是從導像部3 1的端緣（外周轉角）往橫刃斜角3 6構成爲 正視直線形狀，從上述橫刃斜角3 6往上述後跟3 5 (後跟 面3 8 )因考慮到鑽屑的排出性能而構成爲剖視凹彎曲形 狀。 【發明內容】 〔本發明欲解決之課題〕 以該習知例的構成，要成爲如上述般之鑽徑小，長度 -6 - (6) (6)1222387 設置二條鑽屑導引凹槽6 · 7，一條鑽屑導引凹槽的深度 和長度是設定成比另一條鑽屑凹槽的深度還淺但長度較 申請專利範圍第9項記載的印刷配線基板加工用鑽 頭’係於申請專利範圍第6項或第7項記載的印刷配線基 板加工用鑽頭中，鑽頭3爲超硬合金製鑽頭。 申請專利範圍第1 〇項記載的印刷配線基板加工用鑽 頭’係於申請專利範圍第8項記載的印刷配線基板加工用 鑽頭中，鑽頭3爲超硬合金製鑽頭。 【實施方式】 〔發明之實施形態〕 第3圖至第5圖爲表示本發明之一實施例，其說明如 下。 本實施例，是於外周面設有螺旋狀之複數鑽屑排出溝 槽2，在該鑽屑排出溝槽2彼此之間設有導像部1，又於 前端設有鑽刃8之印刷配線基板加工用的鑽頭3，其於鑽 屑排出溝槽2的底部設有往該鑽屑排出溝槽2延伸設置方 向延伸的二條鑽屑導引凹槽6、7之鑽頭。 該鑽頭3爲超硬合金製，例如是採用以平均粒徑爲1 // m以下之碳鎢爲主要成份的超微粒子超硬合金（混合著 鈷、鐽、鉻等）。另，也可採用其他的超硬合金。 設有三條鑽屑排出溝槽2。此外，於鑽屑排出溝槽2 彼此間設有導像部1，並且，採用沒有鏟齒面構成的導像 -10- (7) (7)1222387 部。另外，鑽屑排出溝槽2，是採用各條剖視爲同一形狀 的鑽屑排出溝槽。又，該三條鑽屑排出溝槽2，是設置成 等間隔。 另’本實施例之鑽頭3，從該鑽頭3的前端側看是往 左旋轉進行鑽孔加工的鑽頭，三條鑽屑排出溝槽2從該鑽 頭3的前端側看是設置成右螺旋狀。 二條鑽屑導引凹槽6、7是設置成並設狀態。 該鑽屑排出溝槽2和二條鑽屑導引凹槽6、7 (以下 稱第一鑽屑導引凹槽6、第二鑽屑導引凹槽7)是同時形 成。即藉由磨刀石硏磨先形成第二鑽屑導引凹槽7及導像 部1的一側面，接著，形成第一鑽屑導引凹槽6及所鄰接 之導像部1的一側面以形成鑽屑排出溝槽2和第一鑽屑導 引凹槽6及第二鑽屑導引凹槽7。另外，此時，第一鑽屑 導引凹槽6並不會使在第二鑽屑導引凹槽7所設定的鑽頭 3芯厚減少，並且，是形成爲擴大第二鑽屑導引凹槽7的 寬度（鑽屑排出溝槽2的寬度）。 另，第一鑽屑導引凹槽6及第二鑽屑導引凹槽7,例 如也可以是V字形、U字形、梯形的凹槽等。此外，第_ 鑽屑導引凹槽6及第二鑽屑導引凹槽7也可以是相同或> 同的形狀。 第一鑽屑導引凹槽6及第二鑽屑導引凹槽7，是彳 屑排出溝槽2的前端開始各別延伸設置著。 該第一鑽屑導引凹槽6及第二鑽屑導引凹槽7的_ _ ，第一鑽屑導引凹槽6的深度是設定成比第二鑽屑導;^ -11 - (8) (8)1222387 槽7的深度還淺。藉此，使鑽頭3的芯厚在重視著該鑽頭 3剛性的狀況下主要是由第二鑽屑導引凹槽7來決定，盡 可能不降低鋼性，並且，是由第一鑽屑導引凹槽6確保著 鑽屑排出性影響大之鑽屑排出溝槽2的深度和寬度，使該 鑽屑排出性得以良好地發揮。 此外，第一鑽屑導引凹槽6是比第二鑽屑導引凹槽7 還短，形成爲在前往鑽頭3之底端側的途中就消失。因此 ，對鑽屑排出溝槽2來講第鑽屑導引凹槽6不存在的部份 。是僅由第二鑽屑導引凹槽7來形成鑽屑排出溝槽2。 被引導至鑽屑排出溝槽2內的鑽屑，是藉由第一鑽屑 導引凹槽6及第二鑽屑導引凹槽7的引導作用在鑽屑排出 溝槽2內良好地通過後，於上述第一鑽屑導引凹槽6消失 部位因上述引導作用減弱而往鑽頭3外方移動’逐漸離開 該鑽頭3。 導像部1的前端面是設定成被稱爲是刃腹4的傾斜面 。此外，導像部1的刃腹4，是從鑽頭3的中心軸朝鑽頭 3的外周邊緣傾斜的面。 位於所鄰接之導像部1前端的刃腹4交叉邊’是設定 成直線邊。由於設有三片鑽刃8，所以刃腹4是與其所鄰 接於左右的二條導像部1的刃腹4各別中介著直線邊進行 交叉。該三條直線邊的交點是與鑽頭3的中心軸爲一致的 位置。 藉由該鄰接之刃腹4彼此的交叉’使鑽頭3的前端部 形成著合計爲三條的直線形橫刃5。此外，由於刃腹4爲 -12- (9) 1222387 傾斜，及，三條的直線形橫刃5爲交叉，使鑽頭3的 前端部形成尖銳。 然而，這對上述習知例來講有下述之問題點。 習知例，是設有導像部3 1及鑽刃4 1合計爲二條 謂的二片刃鑽頭·。但是，就二片刃鑽頭而言，是難以 鑽頭3 3的中心前端部硏磨成尖銳。其原因在於二片 頭只有二條導像部3 1，而由導像部3 1的刃腹3 9 (設 像部3 1前端的傾斜面）彼此交叉所形成的橫刃40只 條。因此，於習知例中，就施有要使橫刃40中央部 尖銳的辦法（例如：於導像部的前端形成不同角度的 刃腹使橫刃的中央部形成尖銳）。 鑽頭3 3的中心前端部若不尖銳，在鑽孔開始時 頭3 3的中心位置就容易偏掉，相對地當然會降低貫 的精度。 但是，本實施例，如上述般由於刃腹4爲傾斜且 橫刃5爲交叉著，所以鑽頭3的前端部就形成尖銳， 不需要如習知例般的加工，就可構成鑽孔位置不會偏 鑽頭。 圖中，圖號1 1，是爲要盡可能降低和導像部1 面及由鑽頭3所形成之加工孔內面的抵接面積之段部 實施例的構成，可採用被稱爲具有該段部1 1之所謂 切式（Undercut Type)構成，也可採用不具有段部之所 直切式（Straight Type)構成。 本實施例，爲要在疊層爲多層的印刷配線基板上 中心 之所 將其 刃鑽 在導 有一 形成 二個 的鑽 穿孔 三條 因此 掉的 的外 〇本 的讓 謂的 鑽鑿 -13- (10) (10)1222387 貫穿孔，而構成爲鑽徑小且長度長。此外，鑽頭3的芯厚 (鑽頭3最細部份的直徑），是設定成鑽屑排出溝槽2可 良好地排出鑽屑，並且，是設定成該鑽頭3的強度得以維 持成可良好地發揮筆直前進性的程度。 即使鑽頭3的鑽徑小，但因爲設置在鑽屑排出溝槽2 底部的上述二條鑽屑導入凹槽6、7及形成在該條鑽屑導 入凹槽6、7間的凸條部份可發揮做爲加強肋條的作用， 使鑽頭3變成高強度，並且，可發揮高筆直前進性。 此外，由於設置在鑽屑排出溝槽2底部的上述二條鑽 屑導入凹槽6、7使鑽屑的移動被引導，所以可良好地執 行該鑽屑的排出，防止鑽屑滯留在該鑽屑排出溝槽2內。 另外，因二條鑽屑導入凹槽6、7之中的第一鑽屑導 入凹槽6的長度是比第二鑽屑導入凹槽7的長度還短，所 以鑽屑不會一直都滯留在鑽屑排出溝槽2內，而會從該鑽 屑排出溝槽2排出至鑽頭3的外方，因此就這點而言也可 良好地執行鑽屑的排出。 此外，因鑽頭3前端側的鑽屑排出性能高，所以儘是 如此就可良好地執行鑽屑的排出。 因此，鑽頭3就難彎折，即使鑽徑小且長度長，也能 具高強度並且發揮高筆直前進性，再者，又可防止因鑽屑 滯留在鑽屑排出溝槽2內而造成的工作瑕疵，鑽鑿出內壁 粗糙度爲良好的孔（精度良好的孔）。 另外，因鑽頭3爲超硬合金製，所以其強度當然高， 就這點而言也可發揮高筆直前進性。 -14- (11) (11)1222387 又，於習知例中，因有後跟3 5，從該後跟3 5跨越橫 刃斜角3 6的面（後跟面3 8 )的剖視爲凹彎曲形狀，所以 使該凹彎曲形狀部份抱住鑽屑，但因本實施例是採用沒有 後跟的構成，所以不會有抱住鑽屑的現象發生，因此，就 這點而言也可良好地發揮鑽屑排出溝槽2的鑽屑排出作用 如此，根據本實施例時，因可極良好地發揮鑽屑排出 溝槽2的鑽屑排出作用，所以能夠防止由鑽頭3所鑽鑿的 孔內壁面會因鑽屑而造成粗糙不整，因此，可鑽鑿出精度 良好的孔。 此外，因導像部1是爲三條設置形成的構成，所以由 鑽頭3所鑽鑿的孔與該鑽頭3是在三條導像部1的外周面 進行抵接，因此，藉由三點支撐使該鑽頭3在孔中呈穩定 狀態，如此一來也可發揮高筆直前進性。 另外，鑽刃8的數量也比習知例還多，以相同條件下 進行鑽孔加工時，作用在鑽刃8上的加工負載會減輕，並 且，作用在一條鑽屑排出溝槽2的鑽屑排出負載也會減輕 ，僅是如此就可使鑽孔加工穩定進行，藉此也可發揮高筆 直前進性，並且，可鑽鑿出精度良好的孔。 又，鑽刃8爲三片，合計有三條由鄰接的刃腹4交叉 形成的橫刃5，因該三條橫刃5的交點是形成尖銳，所以 在鑽孔時要決定中心位置的尖銳可簡單地形成在鑽頭3的 中心軸。 以上本實施例因是爲上述般的構成，所以即使鑽徑小 -15- (12) (12)1222387 且長度長，也可成爲具高強度並且發揮高筆直前進性的鑽 頭，再者，又可做爲鑽鑿出的孔內壁粗糙度爲良好之實用 性極佳的印刷配線基板加工用鑽頭。 第6圖、第7圖爲已確認本實施例之效果的實驗結果 。另，第6圖爲表示本實施例之孔位置精度的實驗結果， 第7圖爲表示習之例之孔位置精度的實驗結果。 鑽頭，是使用直徑爲〇. 3 5 m m的小鑽徑型鑽頭。此 外，芯厚爲相同尺寸（規格是重視著良好之內壁粗糙度的 實現而定）。又，要鑽孔的印刷配線基板，是使用總厚度 爲 5 mm之重疊複數片相當於美國電力工業規格（ National Electrical Manufacturers Association )之 F R — 4規格的印刷配線基板。鑽頭的旋轉速度等之加工條件爲 相同。 孔位置，是以重心法求出。 在評估實際所鑽鑿出的孔的分佈是偏離設計上的孔中 心爲何種程度時，於一般上是以設計上的孔中心至實際所 鑽鑿出的孔的中心位置爲止的距離平均，及其與標準偏差 的三倍之和來進行評估，根據該評估，本實施例和習知例 相比約只有60 %之實際所鑽鑿出的孔的中心是沒有偏差 ，由此可確認出是可鑽鑿出非常高精度的孔。 此外，對鑽孔後的印刷配線基板進行電鍍處理在孔中 設有銅電鍍層，然後裁切印刷配線基板，對上述孔的縱剖 面進行放大觀察結果，本實施例，與習知例同爲孔內壁粗 糙度良好。 -16- (13) (13)1222387 即，本實施例之鑽頭3，在被確認是可鑽鑿直徑爲 0.3 5 m m程度，並且，深度爲5 m m以上之孔的鑽頭的同 時，被應確認其是具高筆直前進性，及所鑽鑿出的孔內壁 粗糙度爲良好的雙好鑽頭3。 另外，以目視就可觀察出本實施例在鑽屑排出方面是 比較良好。 另，因鑽頭3的剛性高，所以也可採用朝鑽頭3的底 端側其芯厚會逐漸便大的構成。 又，鑽屑排出溝槽2也可設置成從鑽頭3的前端側看 是爲左螺旋狀。 另，鑽屑排出溝槽2雖然也可爲設置成四條以上的構 成（橫刃5變成四條以上），但從三條導像部1所形成的 三點支撐效果來考量時，或從三條橫刃5的交點必然成一 點的事實來考量時，鑽屑排出溝槽2還是以三條的構成爲 最佳。 又’第一鑽屑導引凹槽6也可構成爲比第二鑽屑導引 凹槽7還長。 〔發明作用及效果〕 由於本發明是在鑽屑排出溝槽2的底部設有往該鑽屑 排出溝槽2延伸設置方向延伸的複數鑽屑導引凹槽6、7 ’因此該複數鑽屑導引凹槽6、7間發揮著做爲加強肋條 的作用，就該點而言可使鑽頭3的強度變高。 因此，鑽頭3就難彎折，即使鑽徑小且長度長，也能 -17- (14) (14)1222387 具高強度並且發揮高筆直前進性。 此外，由於鑽頭3的強度高，所以能夠使其芯厚爲小 以充分確保鑽屑排出溝槽2的深度來進行良好之鑽屑排出 ，防止鑽屑滯留在鑽屑排出溝槽2內造成工作瑕疵。 因此，使用該鑽頭3時，就可鑽鑿出內壁粗糙度爲良 好的孔（精度良好的孔）。 再者，鑽屑的排出是由設置在鑽屑排出溝槽2的底部 的複數鑽屑導引凹槽6、7來引導，因此鑽屑的排出得以 良好進行。 又，根據本發明之申請專利範圍第2項的發明時，由 於複數鑽屑導引凹槽6、7的深度不同，所以較淺的鑽屑 導引凹槽可發揮鑽頭3強度的維持作用，較深的鑽屑導引 凹槽能以高水準發揮鑽屑的排出作用，藉此可達到良好的 鑽屑排出性及由鑽頭高剛性產生的高筆直前進性，即可達 到孔位置精度的提昇。 再者，根據本發明之申請專利範圍第3、4項的發明 時，由於複數鑽屑導引凹槽6、7的長度不同，所以在鑽 頭3的前端側是因該複數鑽屑導引凹槽6、7而得以發揮 高的鑽屑排出性，在鑽頭3的底端側是因長度較短的鑽屑 導引凹槽消失而提高了鑽頭3的強度，因此，可達到良好 的鑽屑排出性及由鑽頭高剛性產生的高筆直前進性’即司* 達到孔位置精度的提昇。 本發明由於是構成爲上述般的構成，所以即使是鑽徑 小且長度長，也可成爲高強度，可發揮高筆直前進性的鑽 -18- (15) (15)1222387 頭，又可做爲鑽鑿出的孔內壁粗糙度爲良好之實用性極佳 的印刷配線基板加工用鑽頭。 【圖式簡單說明】 第1圖爲習知例之說明用正面圖。 第2圖爲習知例之說明用側面圖。 第3圖爲本實施例之說明用透視圖。 第4圖爲本實施例之說明用正面圖。 第5圖爲本實施例之說明用側面圖。 第6圖爲表示本實施例之位置精度實驗結果。 第7圖爲表示習知例之位置精度實驗結果。 〔圖號說明〕 1 :導像部 2 :鑽屑排出溝槽 3 :鑽頭 4 :刃腹 5 :橫刃 6、7 :鑽屑導引凹槽 8 :鑽刃 -19-1222387 (1) 发明 Description of the invention [Technical field to which the invention belongs] The present invention relates to a drill bit for drilling a precision hole in a work piece. [Prior art] A printed wiring board (hereinafter referred to as a printed board) for assembling electronic components is formed by laminating a copper foil on a reinforced fiber resin, drilling a large number of through-holes on the printed board, and then subjecting it to plating. A metal plating layer is formed on the inner wall of the through hole, and then the copper foil on the surface of the printed substrate is etched to form a printed circuit. The printed circuit and the underlying copper foil are passed through the metal plating layer to turn on the power. Electronic parts such as LSI are electrically welded to the above-mentioned through holes to form a printed circuit board. However, in recent years, with the high-performance and miniaturization of electronic devices, the demand for high-density assembly of printed circuit boards has become increasingly high. According to this demand, while the thinning, high-layering, and high-density wiring of printed circuit boards are progressing, the steps of reducing the diameter of the through holes to be drilled in the printed substrates are accelerated. Therefore, the drills used are bound to be used. Be smaller. In addition, in order to improve work efficiency and reduce manufacturing costs, for the through-hole drilling processing on a printed substrate, a plurality of pieces of the printed substrate are stacked to perform through-hole drilling processing. Therefore, the aspect ratio of the through hole (the ratio of the plate thickness to the hole diameter) becomes larger, so a longer drill bit is required. In addition, if the 'bit is longer', the strength required for the bit is relatively increased. Therefore, the drill needs to have high strength. • 5- (2) (2) 1222387 In addition, the deeper the through hole, the more likely it is that the hole will bend. Therefore, the drill needs to have a high straightness. In addition, from an electrical point of view, the drill bit must be able to drill a good inner wall roughness of the through hole on the spot, that is, the drill bit must be able to drill a hole with a smooth inner wall thickness as much as possible. Sorting out the above, it can be seen that the requirements for recent drills for printed circuit board processing are that they must have a small drill diameter, a long length, high strength, excellent straightness, and a rough inner wall of the hole being drilled. The degree is good. On the other hand, Figs. 1 and 2 show drill bits 3 3 (hereinafter referred to as conventional examples) for drilling through holes of a conventional printed circuit board. In this conventional example, a cutting edge 41 is provided at the front end, two spiral drill cuttings discharge grooves 32 are provided on the outer peripheral surface, and a guide portion 3 1 is provided between the drill cuttings discharge grooves 32. Then, A shovel tooth surface 34 having a diameter slightly smaller than the diameter of the drill 33 is provided at a position adjacent to the image guide 31, and a heel 35 is formed on the opposite side of the image guide 31 of the shovel tooth surface 34. Here, the drill cuttings discharge groove 3 2 is formed in a straight line shape from the edge (outer peripheral angle) of the image guide 31 to the beveling edge 3 6, and from the above-mentioned beveling edge 3 6 to the heel 3 5. (Heel surface 3 8) The concave-curved shape is configured in cross-section in consideration of the discharge performance of cuttings. [Summary of the Invention] [Problems to be Solved by the Invention] With the structure of the conventional example, the drill diameter should be small as described above, and the length is -6-(6) (6) 1222387 Two drill chip guide grooves 6 are provided. · 7. The depth and length of one drill chip guide groove are set to be shallower than the depth of another drill chip groove, but the length is longer than that of the printed wiring board processing drill bit described in item 9 of the patent application scope. In the drill for processing a printed wiring board according to the sixth or seventh aspect, the drill 3 is a cemented carbide drill. The drill bit for printed wiring board processing described in item 10 of the patent application scope is the drill bit for printed wiring board processing described in item 8 of the patent application scope, and the drill 3 is a cemented carbide drill. [Embodiment] [Embodiments of the invention] Figs. 3 to 5 show an embodiment of the present invention, and its description is as follows. In this embodiment, a spiral-shaped plurality of drill cuttings discharge grooves 2 are provided on the outer peripheral surface, and a guide portion 1 is provided between the drill cuttings discharge grooves 2 and a printed wiring 8 is provided at the front end. A drill bit 3 for substrate processing is provided with two drill chip guide grooves 6 and 7 at the bottom of the drill chip discharge groove 2 and extending in the direction in which the drill chip discharge groove 2 extends. This drill bit 3 is made of cemented carbide, for example, it is a superfine cemented carbide (mixed with cobalt, samarium, chromium, etc.) mainly composed of carbon tungsten with an average particle diameter of 1 // m or less. Alternatively, other super-hard alloys may be used. There are three drill cuttings discharge grooves 2. In addition, a guide part 1 is provided between the drill cuttings discharge grooves 2 and a guide part -10- (7) (7) 1222387 without a tooth surface is used. In addition, the cuttings discharge groove 2 is a cuttings discharge groove in which each section is cut into the same shape. The three drill cuttings discharge grooves 2 are arranged at regular intervals. On the other hand, the drill 3 of this embodiment is a drill that rotates to the left when viewed from the front end side of the drill 3, and the three cuttings discharge grooves 2 are provided in a right spiral shape when viewed from the front end side of the drill 3. The two drill cutting guide grooves 6, 7 are arranged in a juxtaposed state. The cuttings discharge groove 2 and the two cuttings guide grooves 6, 7 (hereinafter referred to as the first cuttings guide groove 6, and the second cuttings guide groove 7) are simultaneously formed. That is, a second drill cutting guide groove 7 and one side of the image guide 1 are formed by honing stone honing, and then a first drill guide groove 6 and one of the adjacent guides 1 are formed. The side faces are formed with drill cuttings discharge grooves 2 and a first drill cuttings guide groove 6 and a second drill cuttings guide groove 7. In addition, at this time, the first drill cutting guide groove 6 does not reduce the core thickness of the drill 3 set in the second drill cutting guide groove 7, and is formed to enlarge the second drill cutting guide groove. The width of the groove 7 (the width of the drill cuttings discharge groove 2). The first cuttings guide groove 6 and the second cuttings guide groove 7 may be, for example, V-shaped, U-shaped, trapezoidal grooves. In addition, the _th cuttings guide groove 6 and the second cuttings guide groove 7 may have the same shape or > the same shape. The first cuttings guide grooves 6 and the second cuttings guide grooves 7 are respectively extended from the front ends of the cuttings discharge grooves 2. _ _ Of the first cuttings guide groove 6 and the second cuttings guide groove 7, the depth of the first cuttings guide groove 6 is set to be greater than that of the second cuttings; ^ -11-( 8) (8) 1222387 The depth of slot 7 is shallow. With this, the core thickness of the drill bit 3 is mainly determined by the second drill chip guide groove 7 under the condition that the rigidity of the drill bit 3 is emphasized, and the rigidity is not reduced as much as possible, and it is guided by the first drill chip. The guide groove 6 ensures the depth and width of the cuttings discharge groove 2 which has a large influence on the cuttings discharge performance, so that the cuttings discharge performance can be exerted well. The first cuttings guide groove 6 is shorter than the second cuttings guide groove 7 and is formed so as to disappear on the way to the bottom end side of the drill 3. Therefore, the drill chip discharge groove 2 does not exist in the drill chip guide groove 6. The cuttings discharge groove 2 is formed only by the second cuttings guide groove 7. The cuttings guided into the cuttings discharge groove 2 pass through the cuttings discharge groove 2 well by the guiding action of the first and second cuttings guide grooves 6 and 7. Then, at the disappearing part of the first drill cuttings guide groove 6, the drill bit 3 moves away from the drill bit 3 due to the weakening of the guiding effect. The front end surface of the image guide unit 1 is an inclined surface set to be referred to as a cutting edge 4. The blade web 4 of the image guide 1 is a surface inclined from the central axis of the drill 3 toward the outer peripheral edge of the drill 3. The edge 4 of the cutting edge 4 located at the leading end of the adjacent image guide 1 is set to a straight edge. Since the three drill edges 8 are provided, the cutting edge 4 intersects with the cutting edge 4 of the two image guides 1 adjacent to the left and right sides via straight edges. The intersections of the three straight sides are coincident with the center axis of the drill 3. The intersection of the adjacent blade webs 4 with each other 'causes the front end portion of the drill 3 to form three linear transverse edges 5 in total. In addition, since the cutting edge 4 is inclined by -12- (9) 1222387, and the three linear transverse edges 5 are crossed, the front end portion of the drill 3 is sharpened. However, this has the following problems for the above-mentioned conventional examples. The conventional example is a two-blade drill with a guide section 3 1 and a drill edge 41 in total. However, in the case of a two-blade drill, it is difficult to sharpen the center tip of the drill 33. The reason for this is that the two-piece head has only two image guides 31, and 40 blades formed by the flank 39 (the inclined surface at the front end of the image guide 31) of the image guide 31 intersect each other. Therefore, in the conventional example, a method of sharpening the central portion of the horizontal blade 40 is applied (for example, a blade with different angles is formed at the front end of the image guide portion to sharpen the central portion of the horizontal blade). If the center tip of the drill 3 3 is not sharp, the center position of the drill 3 3 will be easily deviated at the beginning of drilling, and the accuracy of the drill will be lowered. However, in this embodiment, since the cutting edge 4 is inclined and the cutting edge 5 is intersecting as described above, the front end of the drill 3 is sharpened, and the drilling position can be configured without the need for processing as in the conventional example. Will be biased. In the figure, the figure number 11 is to reduce the contact area between the surface of the image guide 1 and the inner surface of the processing hole formed by the drill 3 as much as possible. The so-called undercut type structure of the segment portion 11 may also be a straight type structure without the segment portion. In this embodiment, the blade is drilled in the center of a multilayer printed wiring board laminated with a drill hole formed by two drill holes, and three drill holes are drilled. This is a 13- ( 10) (10) 1222387 The through-hole has a small drill diameter and a long length. In addition, the core thickness of the drill 3 (the diameter of the thinnest part of the drill 3) is set so that the drill cuttings discharge groove 2 can well discharge the cuttings, and the strength of the drill 3 is maintained so that it can be maintained well. Extent of straight forwardness. Even if the drill diameter of the drill bit 3 is small, it is possible because the two drill cuttings introduction grooves 6 and 7 provided at the bottom of the drill cuttings discharge groove 2 and the convex portion formed between the drill cuttings introduction grooves 6 and 7 can be used. It functions as a reinforcing rib to make the drill bit 3 high-strength and to exhibit high straight forwardness. In addition, since the two cuttings introduction grooves 6 and 7 provided at the bottom of the cuttings discharge groove 2 guide the movement of the cuttings, the discharge of the cuttings can be performed well, and the cuttings can be prevented from staying in the cuttings. It is discharged into the groove 2. In addition, since the length of the first cuttings introduction groove 6 among the two cuttings introduction grooves 6 and 7 is shorter than the length of the second cuttings introduction groove 7, the cuttings will not stay in the drill all the time. The cuttings are discharged from the cutting grooves 2 to the outside of the drill 3 from the cuttings discharge grooves 2. Therefore, the cuttings can be discharged well in this regard. In addition, since the cutting chip discharge performance is high on the front end side of the drill bit 3, it is possible to perform the discharge of the cutting chips well. Therefore, the drill bit 3 is difficult to bend. Even if the drill diameter is small and the length is long, it can have high strength and high straight forward performance. Furthermore, it can prevent the drill cuttings from being trapped in the drill cuttings discharge groove 2 and caused. Work flaws, drilling holes with good inner wall roughness (holes with good accuracy). In addition, since the drill 3 is made of cemented carbide, its strength is naturally high, and high straight forwardness can be exhibited in this regard. -14- (11) (11) 1222387 Also, in the conventional example, since there is a heel 3 5, a cross-section of the face (heel surface 3 8) across the bevel 3 6 from the heel 3 5 It is a concavely curved shape, so the concavely curved shape partially holds the drill cuttings. However, since the embodiment has a structure without a heel, the phenomenon of holding the cuttings does not occur. Therefore, in this regard, The cuttings discharge function of the cuttings discharge groove 2 can also be effectively exerted. According to this embodiment, the cuttings discharge function of the cuttings discharge groove 2 can be excellently performed, so that drilling by the drill 3 can be prevented. The inner wall surface of the drilled hole will be rough and rough due to the cuttings. Therefore, a high-precision hole can be drilled. In addition, since the image guides 1 are formed in three rows, the holes drilled by the drill 3 and the drill 3 are in contact with the outer peripheral surfaces of the three image guides 1. Therefore, the three-point support This drill bit 3 is in a stable state in the hole, so that high straight forwardness can also be exhibited. In addition, the number of drill edges 8 is more than the conventional example. When drilling is performed under the same conditions, the machining load acting on the drill edges 8 is reduced, and a drill acting on a cuttings discharge groove 2 is drilled. The chip discharge load is also reduced, so that the drilling process can be performed stably, thereby achieving high straight forward performance, and capable of drilling holes with high accuracy. In addition, the drill edge 8 is composed of three pieces, and a total of three cutting edges 5 formed by the intersection of adjacent cutting edges 4 are formed. Since the intersection of the three cutting edges 5 is sharp, it is easy to determine the sharpness of the center position when drilling. Ground is formed on the central axis of the drill 3. The above embodiment has the structure as described above, so even if the drill diameter is small -15- (12) (12) 1222387 and the length is long, it can be a drill with high strength and high straight forward performance. Furthermore, It can be used as a drill for printed wiring board processing with excellent practicability. Fig. 6 and Fig. 7 are experimental results in which the effect of this embodiment has been confirmed. FIG. 6 is an experimental result showing the hole position accuracy of this embodiment, and FIG. 7 is an experimental result showing the hole position accuracy of the example. The drill is a small-diameter drill having a diameter of 0.35 m. In addition, the core thickness is the same size (specification is based on the realization of good inner wall roughness). In addition, the printed wiring board to be drilled is a printed wiring board with a total thickness of 5 mm, which is equivalent to the F R-4 specification of the National Electrical Manufacturers Association. The processing conditions such as the rotation speed of the drill are the same. The position of the hole was determined by the method of gravity. When assessing the extent to which the distribution of actually drilled holes deviates from the center of the designed hole, the average is generally the distance from the center of the designed hole to the center of the hole actually drilled, and It is evaluated by the sum of three times the standard deviation. According to the evaluation, there is no deviation in the center of the hole actually drilled only about 60% compared with the conventional example, so it can be confirmed that Very precise holes can be drilled. In addition, the printed wiring board after the drilling is plated with a copper plating layer in the hole, and then the printed wiring board is cut, and the longitudinal section of the hole is enlarged and observed. This embodiment is the same as the conventional example. The inner wall roughness of the hole is good. -16- (13) (13) 1222387 That is, the drill 3 of this embodiment is confirmed to be a drill capable of drilling a hole having a diameter of approximately 0.3 5 mm and a depth of 5 mm or more. It is a double good drill bit 3 with high straight forwardness and good inner wall roughness of the hole being drilled. In addition, it can be observed visually that this embodiment is relatively good in terms of cuttings discharge. In addition, since the drill 3 has high rigidity, a configuration in which the core thickness gradually becomes larger toward the bottom end side of the drill 3 may be adopted. The cuttings discharge groove 2 may be provided in a left spiral shape when viewed from the front end side of the drill 3. In addition, although the cuttings discharge groove 2 may be provided with four or more pieces (the horizontal blade 5 becomes four or more), when considering the three-point support effect formed by the three image guides 1, or three horizontal blades In consideration of the fact that the intersection point of 5 must be a little, when considering the drill cuttings discharge groove 2, a three-piece structure is the best. The first cuttings guide groove 6 may be longer than the second cuttings guide groove 7. [Inventive Actions and Effects] Since the present invention is provided with a plurality of drill cutting guide grooves 6, 7 'extending in the direction in which the drill cuttings discharge groove 2 extends, the plurality of drill cuttings are provided at the bottom of the drill cuttings discharge groove 2. The guide grooves 6 and 7 play a role as reinforcing ribs, and in this regard, the strength of the drill 3 can be increased. Therefore, the drill bit 3 is difficult to bend. Even if the drill diameter is small and the length is long, it can have high strength and high straight forward performance. In addition, due to the high strength of the drill bit 3, the core thickness can be made small to sufficiently ensure the depth of the cuttings discharge groove 2 for good cuttings discharge, preventing the cuttings from staying in the cuttings discharge groove 2 and causing work. defect. Therefore, when this drill bit 3 is used, it is possible to drill a hole having a good inner wall roughness (a hole with a high accuracy). Furthermore, the discharge of the cuttings is guided by the plurality of cuttings guide grooves 6, 7 provided at the bottom of the cuttings discharge groove 2. Therefore, the discharge of the cuttings can be performed well. In addition, according to the invention of the second patent application scope of the present invention, since the depth of the plurality of cuttings guide grooves 6 and 7 is different, the shallower cuttings guide grooves can maintain the strength of the drill 3, The deeper cuttings guide groove can play the cuttings discharge function at a high level, thereby achieving good cuttings discharge and high straight forwardness caused by the high rigidity of the drill bit, which can improve the accuracy of hole position. . In addition, according to the invention of claims 3 and 4 of the present invention, since the lengths of the plurality of cuttings guide grooves 6 and 7 are different, the leading edge of the drill 3 is caused by the plurality of cuttings guide grooves. The grooves 6 and 7 can exhibit high cuttings discharge performance. At the bottom end side of the drill 3, the strength of the drill 3 is increased by the disappearance of the shorter cuttings guide grooves. Therefore, good cuttings can be achieved. Evacuation and high straight forwardness due to the high rigidity of the drill bit, which means that the accuracy of the hole position is improved. Since the present invention is structured as described above, even if the drill diameter is small and the length is long, it can be a high-strength drill that can exhibit high straightness. -18- (15) (15) 1222387 can also be made A drill for processing a printed wiring board which has a good inner wall roughness for drilling a hole. [Brief description of the drawings] FIG. 1 is a front view for explaining a conventional example. Fig. 2 is a side view for explaining a conventional example. Fig. 3 is a perspective view for explaining the embodiment. Fig. 4 is a front view for explaining the embodiment. Fig. 5 is a side view for explaining the embodiment. Fig. 6 shows the results of the position accuracy experiment of this embodiment. Fig. 7 shows the results of the position accuracy experiment of the conventional example. [Illustration of drawing number] 1: Guide part 2: Drill chip discharge groove 3: Drill bit 4: Cutting edge 5: Horizontal blade 6, 7: Drill chip guide groove 8: Drill edge -19-