單片玻璃基板以刀輪切割後之彎曲破壞行為

Abstract

本研究主要探討單片式顯示器玻璃基板，在母玻璃切割成單片玻璃的製程中對於玻璃彎曲強度的影響，藉此研究來選擇最佳化的製程材料及條件，進而優化製程及提高生產良率，並使終端產品獲得更佳之機械性質。本文選用光學玻璃是薄膜電晶體(Thin Film Transistor)專用的母基板(Mother Glass)，於切割製程中使用不同角度的切割刀輪搭配不同的切割負載條件，將玻璃母基板切割裂片成較小的玻璃基板後，以高倍率的顯微鏡觀察切割後玻璃基板所生成的裂紋狀況，記錄及量測切割所造成之縱向裂紋、橫向裂紋及表面裂紋結果。再透過四點彎曲測試(4 Point Bending)量測各組切割條件的光學玻璃彎曲之強度，並獲得一個較佳的結果組合。 藉由切割條件、三軸向裂紋長度、彎曲強度分類比較。結果指出，不同的切割刀輪搭配適當的製程參數對於切割後的玻璃基板四周微裂痕(Micro Crack)有很大的差異，而這些微裂痕影響了光學玻璃的機械強度，其中以縱向裂紋及橫向裂紋較為顯著。縱向裂紋與橫向裂紋呈現相依性，均會隨著負載加大而增長，對於同樣的負載而言刀輪角度越大，縱向及橫向裂紋會相對較短;表面裂紋則隨著刀輪角度及切割負載的增加而變長。 影響彎曲強度主因為橫向裂紋及縱向裂紋，表面裂紋並不明顯，縱向裂紋深度不足時會造成裂面不平整，並在裂面產生微小塑性變形區及微裂痕，使得彎曲強度減弱;而縱向裂紋的深度過深則會造成玻璃內部橫向裂紋增生成長，實驗證實橫向裂紋既為彎曲強度減弱的主因，大幅影響光學玻璃切割後強度的品質。 就我們實驗的康寧1737光學玻璃而言，較佳的切割條件為使用120°切割刀輪搭配20牛頓的負載壓力;光學玻璃切割後的品質確認，最重要即為縱向裂紋，縱向裂紋深度不足時，會使得裂面不平整並在裂面產生微小塑性變形區及微裂痕，使得彎曲強度減弱;縱向裂紋的深度過深則會造成玻璃內部橫向裂紋的數量及長度增加，玻璃越厚需以越大角度之刀輪切割。

The research aim to investigate failure behaviors of single sheet glass subjected to bending loading. Glass is a brittle material and it breaks without significant strain while micro cracks in glass surface subjected to bending loading. But glass is often used in our daily life, such as commercial flat display panel of glass substrates. To enhance the modulus of rupture and increase life time of display glass, we must find ways to reduce micro cracks during display glass manufacturing processes, one possible way is to improve display scribing process. The scribing process is widely used for sizing of display glass sheets. Scribing wheel is used to generate a median crack on the top of glass surface for sizing display sheets. But is will generate a lateral and a surface crack during scribing process as well. These three basic types of cracks will cause of glass breaks while it subjected to bending stress in further applications. This paper proposes a method to optimal scribing conditions to get higher modulus of rupture and obtains the relationships between three basic types of micro crack and scribing conditions. First step is to generate a matrix of experimental parameters for the key scribing factors of wheel angle and scribing load, then determine three basic types of crack depth and length distributions for each specimen by visual inspection via optical microscopy, the last is to get the modulus of rupture for each specimen, four point bending is a common way for strength of glass by flexure. The specimen was placed horizontally on two support rods with cracks surface face down, then load the specimen at a constant rate till to glass failure. The result that modulus of rupture can be improved by modification of wheel angle and cutting loading. The best modulus of rupture was performed by a wheel angle and cutting loading, the best modulus of rupture was performed by a wheel having 120 degree tip angle and 20 Newton cutting loading. Micro cracks consists of median、lateral and surface cracks generated during scribing process, it was found that lateral crack length is related to the dimension of median cracks, the lateral cracks begin to appear after cutting wheel unloading due to relaxation of intense residual stresses on scribing filed. Once single glass subjected a bending loading, the lateral cracks continue to propagated till to glass rupture.