Study on Improving Thickness Uniformity of Microfluidic Chip Mold in the Electroforming Process

Abstract

Electroformed microfluidic chip mold faces the problem of uneven thickness, which decreases the dimensional accuracy of the mold, and increases the production cost. To fabricate a mold with uniform thickness, two methods are investigated. Firstly, experiments are carried out to study how the ultrasonic agitation affects the thickness uniformity of the mold. It is found that the thickness uniformity is maximally improved by about 30% after 2 h electroforming under 200 kHz and 500 W ultrasonic agitation. Secondly, adding a second cathode, a method suitable for long-time electroforming is studied by numerical simulation. The simulation results show that with a 4 mm width second cathode used, the thickness uniformity is improved by about 30% after 2 h of electroforming, and that with electroforming time extended, the thickness uniformity is improved more obviously. After 22 h electroforming, the thickness uniformity is increased by about 45%. Finally, by comparing two methods, the method of adding a second cathode is chosen, and a microfluidic chip mold is made with the help of a specially designed second cathode. The result shows that the thickness uniformity of the mold is increased by about 50%, which is in good agreement with the simulation results.

Fabrication of metal microfluidic chip mold with coplanar auxiliary cathode in the electroforming process

“…The researches [13,24] have shown that the width of auxiliary cathode and the distance between auxiliary cathode and the microstructure have direct effect on thickness uniformity of the electroformed microstructure. In order to quickly determine the dimensions and placement of auxiliary cathode, the computer-aided analysis is performed to simulate electroforming process.…”

“…But for longtime electroforming, the high temperature and pressure caused by ultrasonic cavitation may destroy the photoresist structures [21], which limits the application of ultrasonic electroforming to a certain extent. Because electric field distribution directly determines the thickness uniformity of micro electroforming, the methods of optimizing electric field distribution, such as auxiliary cathode [13,[22][23][24] and insulating shield [25] have been developed. The auxiliary cathode method is a more effective way to decrease the edge effect of current in micro electroforming than insulating shield method.…”

“…The auxiliary cathode method is a more effective way to decrease the edge effect of current in micro electroforming than insulating shield method. The auxiliary cathode is usually metal ring or frame around the cathode, and is placed in some distance from the electroformed surface [22][23][24]. During the electroforming process, the auxiliary cathode can consume some current from the edge of the cathode and then improve the thickness uniformity of electroforming.…”

Electrodeposition model with dynamic ion diffusion coefficients for predicting void defects in electroformed microcolumn arrays

“…Nowadays, there is an increasing demand for micro structures of micron-scale line widths and high aspect ratios due to the rising functionality of micro-devices. With the advantages of precision features, ultra-smooth surface finish and mass production capability, the LIGA technique has emerged as the suitable method for large-scale fabrication of micro-devices, such as microfluidic chips, [1][2][3] micro-molds, 4,5 and optical systems. 6,7 As one of the major steps in LIGA, micro-electroforming has the ability to accurately replicate patterned micro molds through the deposition of metal atoms and consequently plays an increasingly important role in the manufacture of mold inserts.…”

3D Printing of Metallic Microstructured Mould Using Selective Laser Melting for Injection Moulding of Plastic Microfluidic Devices

“…This process demonstrates high precision but requires expensive masters and takes several weeks to complete the entire process. The thickness uniformity and flatness can be constrained when growing thick deposits [2].…”