The Technology of Micro Adhesive Bonding
Innovation via micro adhesive
For the assembly of microparts screws are quite useless, in particular
when they are 10 times bigger than the microsystem. Micro adhesive bonding
is in most cases the only possible solution. But the properties of adhesives
in small dimension can be totally different to those in classical macroscopic
dimensions. Adhesives suitable for a similar macroscopic task, can be
completely unsuitable on the microscopic scale. In the same way the handling
of adhesive materials is different: smallest amounts are necessary, they
have to be placed very precisely and may be swallowed by capillarity into
the microstructure. The transport of a single drop with defined size must
be provided, as well as the fast in-line curing of adhesives with a high
precision of the bond or two stage cure processes.
- Conductive joints in dynamically stressed systems such as electronics
in automotive components
- Thermal management (high density packing of microelectronics)
- Fiber optic couplers, electro-optic transducers (telecommunications)
- High definition sealing in micro-fluidics (biotechnology, life sciences)
Advantages by micro adhesive bonding:
- Joining of many dissimilar materials
- Multi-functionality of the joint (e.g. mechanical fastening plus conductivity)
- Low heat / cold joining
- Low mechanical stress, uniform stress distribution
- Galvanic isolation of the parts (no contact corrosion)
- New freedom for design
- Innovative technical solutions
Development of an adhesive bonding process:
The development of an adhesive bonding process involves the following
- Selection and development of the adhesives
- Precise application of minute volumes of the adhesives
- Compatibility with the micro-assembly process on the Micro Production
- Adhesive curing (e.g. rapid cure, two-stage cure)
- Micro-testing of the joint (quality assurance)
All this special knowledge on micro adhesive bonding in combination with
the Micro Production System
is provided by our partner, the Fraunhofer institute IFAM.
Micro Adhesive Bonding Modules
as Part of our Micro Production System
Klocke Nanotechnik learned a lot from the experience of IFAM and developed
a special dispenser for spending small amounts of adhesives, see Fig.
6. This dispenser can be used manually and is remote controlled by our
Network Controller. It offers shortest pulses as well as continuous dispensing.
Dispensers can be programmed like all other axes in our Micro Production
System. A typical process like:
1. Find a micropart and move it under the gripper,
2. Lift it up with the gripper,
3. Spend a drop of adhesive onto the target position,
4. Place the micropart at the target position,
5. Cure the adhesive
... is programmed easily by drag-and-drop in a few minutes.
Besides individual commands to the dispenser software
modules are available to produces arrays of small adhesive dots (Fig.
1 and 2).
Lines of adhesive and a profile of one line
3D-data set of an area around this line of adhesive. The red marker defines
Assembly and alignment in
the same process:
The Micro Production System includes Software for the alignment of objects.
At first the axes for movement during alignment and the input signal can
be selected. Then parameters for a coarse search are entered, to find
the first signal for a closed loop. After this signal is reached the program
enters a fine positioning loop with own parameters to find the maximum
signal intensity in a selectable amount of cycles. Fig. 5 shows an assembled
VCSEL-Diode glued into an SMD housing after this active alignment.
Sharpen a hair...
... or bring a tip onto the end of a glass fiber and focus it!
This microassembly example of a detection element in Scanning Nearfield
Optical Microscopes (SNOM) needs a resolution of better 20 nm2.
A pyramid-shaped microtip is glued onto the end of a glass fiber. A 150
nm small hole in that tip forms a lens as sub-wavelength light source.
The adhesive bonding process requires a very high precision. During the
active alignment and the following curing of the adhesive, laser light
is coupled through the glass fiber. The light emission of the microtip
is used as feedback signal for the alignment. A misalignment of only 30
nm is clearly visible. The glass fiber with such a pinhole at its end
then is assembled beside a shear force sensor. This device is used as
central detection element in SNOMs. The following SEM picture shows the
a) Cantilever with microtip
b) Glass fiber
c) Shear force sensor
"Gap" = area that has to be filled with adhesive: Have fun!
The amount of adhesive applied between the parts a, b and c in the "Gap"-area
is critical: too much adhesive and the shear force sensor is damped. Too
little adhesive allows for the cantilever of the microtip to oscillate
freely. In both cases the device would be destroyed. The adhesive is applied
with one of the Nanorobotics manipulators,
... and it can be even more complex:
Generation of 3-D adhesive
A 3-dimensional path on the surface of a micropart can be generated in
the following way:
- The micropart is moved by joystick under a microscope. Each key-click
at the joystick stores one position (X,Y, Rotation). This 2-D dataset
is used to calculate a 2-D path.
- An FRT Microprof® sensor attached to the Micro Production
System determines the height along this 2-D path and generates the dataset
of the third dimension.
- Afterwards the adhesive dispenser moves along this path (with the
help of a 4-axis path control electronics and software) and generates
3-D adhesive structures onto the micropart.
Using a conductive adhesive leads to "wires"
on microstructures that are placed without heat treatment directly during
the assembly process. Fig. 1 shows how small structures of conductive
adhesives can be.