Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-07-27
2001-09-18
Aftergut, Jeff H. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S275700, C156S289000, C156S293000, C156S305000, C156S308200, C285S124200, C285S124400, C285S124500, C427S255600, C427S256000, C427S428010, C427S901000
Reexamination Certificate
active
06290791
ABSTRACT:
The present invention relates to fluid connections, in particular to a fluid connection between an inlet capillary or other small bore tube and a microengineered fluidic structure. Hereinafter the term “small bore tube” is taken to include capillary tubes and non-capillary tubes.
There is a growing interest in microengineered structures for transporting microscopic amounts of fluid, wherein the fluid is subject to chemical and/or biochemical processing and analysis. In particular our copending application WO96/12541 describes and claims method and apparatus for carrying out a diffusive transfer process between first and second immiscible fluids, wherein first and second flow paths communicate with one another in a region which is such as to permit the fluids to form a stable open interface therein, and wherein the flow paths in the interface region have a width normal to the interface within the range 10 to 500 micrometers. As described, the apparatus is typically constructed by etching grooves in the surface of a silicon sheet, to form fluid flow channels, and to bond a cover layer of glass onto the silicon sheet. However the application does not address in detail the problem of making an external connection to the microengineered device. It is desirable in this and many other applications of microfluidic devices, especially for analysis or where fluids within the devices are to be monitored or controlled, that connections be formed to external tubing without formation of excessive dead spaces or stagnant areas. This can require connection of the microfluidic device channels to capillary tubing of similar cross sectional dimensions.
Methods of making connections to capillary tubes are extremely well documented and are very diverse, depending on the specific application. For example, an end of the glass capillary may be surrounded by a plastic sheath for fixing securely in an inlet aperture of an apparatus, see for example EP-A-0698789 which describes a connection of capillary tubing to high pressure liquid chromatography apparatus. However, making a force fit with a flexible sheath or other insert would not be suitable for such a delicate microengineered structure as described in our above copending application. Further conventional connector structures for connection to circular cross section capillary tubes by conventional procedures require structures with a recess of circular cross section, sometimes tapered, which are generally unavailable with microengineered devices, and generally with dimensions greater than the thickness of substrates conventionally used for construction of microengineered structures. For the purposes of the specification, microengineered structures is intended to mean structures formed with one or more than one stacked substrates, each substrate being of generally planar form and of a thickness preferably 2 mm or less, and having fluid flow channels formed therein, at least parts of such channels having a cross-sectional diameter less than 1000 micrometers. It will be understood that diameter is intended to mean the thickness or width for non-circular cross sectional channels. It will further be appreciated that such channels may be extended in specific regions to form chambers etc. within the structure with dimensions greater than 1000 micrometers. The substrates are commonly formed from silicon, glass, ceramics, plastics or metal.
Connection of capillary tubes (commonly having dimensions between 50 and 1000, desirably between 100 and 300 micrometers external diameter) to microengineered structures, especially those formed by bonding planar etched or formed substrates, generally requires low stress joining techniques. High temperature processes such as required to weld metals, ceramics, or glasses may generate damage such as substrate cracking or delamination. Within relatively thin (generally <2 mm) substrates, especially in ceramics or glass, the formation and maintenance of threaded, interference, or compression joints is not well established. Sealing of joints usually therefore requires use of sealing material.
In Reston & Kolesar “Silicon-Micromachined Gas Chromatography System—Part 1”, Journal of Micromechanical Systems, IEEE/ASME, December 1994, page 139 there is shown a method of connecting a gas inlet tube to a gas chromatograph comprising a spiral flow path, 300 &mgr;m wide and 10 &mgr;m deep, etched into the surface of a silicon wafer substrate. A glass plate is bonded to the upper surface of the substrate over the spiral flow path, and a tapered gas feed through an aperture is formed in the lower surface of the silicon wafer communicating with the spiral flow path. An end of a gas inlet tube, 254 &mgr;m in diameter, is inserted into the tapered aperture, and an adhesive (epoxy resin) is applied around the end of the inlet tube and the open part of the aperture in order to seal the tube within the aperture.
There are a number of problems and disadvantages associated with such an arrangement where the capillary tubes enters the device perpendicular to the plane of substrates and the fluidic structures formed in those substrates. One problem is that having a capillary tube connection perpendicular to planar substrates and devices interferes with stacking of such substrates and devices to produce compact systems. Another problem is that formation of vias through substrates for connection of capillary tubes perpendicular to substrates can excessively complicate device fabrication and reduce achievable device density and yields. Formation of vias through substrates with near parallel or slightly tapered bores matched to capillary tube dimensions can be difficult. For structures etched in glass or silicon the masking and etch time requirements for the deep etching required for formation of such vias can be much more restrictive than those required for etching the fluidic channel structures into the substrate surface.
Another problem with such an arrangement is that the length of capillary tube enclosed within the substrate is limited to the thickness of the substrate, and that the length of adhesive bond supported intimately by the outer wall of the capillary tube and bore through the substrate is similarly limited to the thickness of the substrate. This can result in a relatively weak and fragile seal. Application of further adhesive around the capillary and onto the outer surface of the substrate may improve seal quality, but the improvement is often limited by poor bonding to planar substrate surfaces. Application of further adhesive around the capillary and onto the outer surface of the substrate may also be undesirable due to the resultant increase in unit volume and interference with packing together of units into a system. Similarly, bonding of conventional capillary connectors onto the substrate surface over a via may give poor seal quality, increase the area required for individual devices, and interferes with device packing and stacking.
Another problem with such arrangements is that feeding adhesive materials into the region between the capillary tube outer wall and the sides of the via bore sufficiently well to form a seal, but without adhesive entering and blocking or contaminating the fluidic channels and the capillary tube itself, can be difficult. It is generally necessary to use adhesive formulations of sufficiently high viscosity to prevent rapid flow of adhesive by capillary action into the fluidic channels. It is, however, generally difficult to observe or monitor and control how well the adhesive has fed into the via regions desired.
A further problem with such arrangement is, particularly for gases, that the fluid must flow into the microengineered structure in a direction perpendicular to the direction of the fluid channels within the structure and that the movement of the fluid through a right angle may create turbulence or other recirculating or mixin, processes and create flow conditions which are difficult to predict.
SUMMARY OF THE INVENTION
In a first aspect the present invention provides a method of connecting
Corless Anthony Robert
Dodgson John Robert
Shaw John Edward Andrew
Turner Chris
Aftergut Jeff H.
Bollman William H.
Central Research Laboratories Limited
Tolin Michael A.
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