Drilling of Glass for Access-Hole Formation

In order to provide liquid access to the microfluidic chips, holes are usually created on the cover plate. These access holes are usually created on glass by drilling using diamond drill bits. However, other methods have also been used, and these are summarized in Table 2.4. 

Drilling has also been performed on the bonded plate, rather than on the cover plate before bonding. To avoid plugging the channel in the bonded plate with glass particles during drilling, the channel was filled with Crystal Bond [132]. 

In some cases, drilled holes are created on the same plate where the channels are etched. To achieve this, the holes were drilled either on the channel plate, or on a plain plate with subsequent channel etching [13,134]. In the latter case, the photoresist can only be sprayed, rather than spin-coated on the drilled glass plate [134], 

Drilling by a diamond-tipped drill bit (15 s per hole) is much faster than ultrasonic drilling (15 min per hole). On the other hand, ultrasonic drilling allows all holes to be drilled simultaneously with a multi-tipped ultrasonic drill bit [ 108]. 

HF etching (4 min, 1 mm dia., 145 um deep) C02 laser drilling Ultrasonic abrasion Electrochemical discharge machining Powder blasting 

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