# The SMARTLAM 3D-I Concept: Design of Microsystems from Functional Elements Fabricated by Generative Manufacturing Technologies

Markus Dickerhof, Daniel Kimmig, Raphael Adamietz, Tobias Iseringhausen, Joel Segal, Nikola Vladov, Wilhelm Pfleging, Maika Torge

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## To cite this version:

Markus Dickerhof, Daniel Kimmig, Raphael Adamietz, Tobias Iseringhausen, Joel Segal, et al.. The SMARTLAM 3D-I Concept: Design of Microsystems from Functional Elements Fabricated by Generative Manufacturing Technologies. 7th International Precision Assembly Seminar (IPAS), Feb 2014, Chamonix, France. pp.147-160, 10.1007/978-3-662-45586-9_19. hal-01260754

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Submitted on 22 Jan 2016

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# The SMARTLAM 3D-I Concept: Design of Microsystems from functional elements fabricated by generative manufacturing technologies

Markus Dickerhof¹, Daniel Kimmig¹, Raphael Adamietz², Tobias Iseringhausen², Joel Segal³, Nikola Vladov³, Wilhelm Pfleging⁴, Maika Torge⁵

¹Institute for Applied Computer Science, Karlsruhe Institute of Technology, Karlsruhe, DE,

²Fraunhofer Institute for Process Automation, Stuttgart, DE,

³Manufacturing Research Division, Faculty of Engineering, University of Nottingham, Nottingham, UK

⁴Institute for Applied Materials Karlsruhe Institute of Technology, Karlsruhe, DE,

⁵Karlsruhe Nano Micro Facility, H.-von-Helmholtz-Platz 1, 76344 Egg.-Leopoldshafen, DE

## Abstract

Generative manufacturing technologies are gaining more and more of importance as key enabling technologies in future manufacturing, especially when a flexible scalable manufacturing of small medium series of customized parts is required. The paper describes a new approach for design and manufacturing of complex three dimensional components building on a combination of additive manufacturing and e-printing technologies, where the micro component is made up of stacks of functionalized layers of polymer films. Special attention will be paid to the “3-d” modeling approach, requested to support the applicaton developer through provision of design rules for this integrated manufacturing concept. Both, the application concept as well as the related equipment and manufacturing integration currently are currently developed further in the project SMARTLAM, funded by the European Commission.

**Keywords:** flexible scalable manufacturing, smart manufacturing, additive manufacturing, printing technologies.

## 1 Introduction

Today’s fabrication methods for micro and nanotechnology enabled devices require expensive tooling and long turnaround times, making empirical, performance-based modifications to the product design expensive and time consuming. Thus till to date are often limited in their flexibility, so that complex devices, that incorporate on-board valves, membranes, discrete parts, or electrodes, cannot be developed or adapted without considerable expense in molds and assembly fixtures.

These boundary conditions create a barrier to the development of small to mediul series of complex and higher functionality devices, where the cost-benefit ratio of incorporating functionality is too risky for the typical laboratory, diagnostic or medical device developer. To bridge the gap between a high volume production with specialized equipment and a - until today - not efficient production of medium series, SME’s need to find other, more flexible and scalable approaches to produce microsystems in high volumes.

The solution proposed by the EC-funded project SMARTLAM and presented in this paper builds on a modular, flexible, scalable scenario combining state of the art developments in technologies and materials:

- Rapid prototyping technologies in a wider sense and laminated object manufacturing (LOM) in the narrow sense - an established rapid prototyping technology building on layer by layer lamination of functionalised film sheets with different material properties is in the focus of the activities [1].

- Printing technologies, where aerosol-jet printing is

in the specific focus of the project allowing for an efficient and precise manufacturing of conductive tracks, electrodes, etc.

Novel polymer film materials with advanced material properties such as anisotropic conductive film or effects arising from combinations of composite sheets will be combined with state of the art, scalable 3D printing, structuring and welding technologies as well as the usage of.

Both technologies will be integrated in a modular manufacturing environment allowing for the production of complete 3D Microsystems.

<figure><img src="image_3.png" /><figcaption>Fig. 1. SMARTLAM enabling technologies.</figcaption></figure>
The approach proposed by SMARTLAM is
designed to address the manufacturing of small
medium series of micro enabled components, in
contrary to the research field of roll-to-roll
manufacturing focussing on a high throughput
manufacturing of e-printed devices such as flexible
electronics, flat panel displays or organic
photovoltaics [2].

The SMARTLAM design approach builds on the
assumption that most applications can be designed
using modular building blocks with dedicated process
sequences for each functional element – the 3
dimensional integration (3D-I) approach.

To allow for a better use of the new capabilities
arising from this 3D-Integration a testbed will be set
up and evaluated by two SME companies in the field
of bioanalytics and lighting application. The
companies are acting as potential customers, whose
application requirements will be providing input to the
3D-I approach from a technical and economical
perspective.

## 2. Application oriented modeling elements of the SMARTLAM 3D-I approach

To facilitate the development of new applications
the SMARTLAM consortium introduced a modelling
hierarchy allowing for structuring of the different
levels of detailing and the mapping of technological
capabilities, after the initial function requirements
have been clarified and a first decision for a specific
design has been made.

Over the first months the focus of the
discussions was on the identification of an initial set
of functional elements which will become expanded
during the project. Sets of related process sequences
for manufacturing are currently identified for each of
these elements These specific process chains
support the implementation of a specific functional
element, representing an instance of more or less
application independent manufacturing processes.

* SMARTLAM APPLICATION
  (e.g. bio disposable)

* SMARTLAM FUNCTIONAL ELEMENT
  (functional block, e.g. mixer or
  integrated IC)

* SMARTLAM FEATURES
  smallest functional element (e.g. groove,
  a printed line)

* SMARTLAM ENABLING TECHNOLOGIES
  for manufacturing of feature
  Simple case:
  laser milling of a groove or hot embossing
  More complex case:
  „Via" consisting of milled throughole, filling of
  hole by printing → mapping of

<figure><img src="image_4.png" /><figcaption>Fig. 3. SMARTLAM modeling hierarchies.</figcaption></figure>

## 2.1 Modelling of generic SMARTLAM functional elements

This initial set of functional elements shall cover
a broad variety of potential applications without being
limited to the two main application fields, which are in

the focus of SMARTLAM.

The requirements to the functional elements
have to address the manufacturing methods inherent
to SMARTLAM: They should either

- have the potential to become realised by a
combination of the technologies available in one
level (grooves, conductive tracks,...), or

- can be manufactured by a combination of layers
with different properties, e.g. a valve, realised by
an elastomer layer in between two rigid layers
with circular cut outs.

Fig. 2 provides an example for a (hypothetic)
disposable for bio analytics device, in which fluidic
and electronic functional elements had been
combined by an "intelligent" combination of layers of
functionalised polymers with different material
properties. Besides functionalised layers, e.g. for e-
contacting, layers with dedicated material properties
or micro structured layers examples for integration of
discrete parts are included, Positioning and
contacting of a discrete chip or a battery widens the

<figure><img src="image_5.png" /><figcaption>Fig. 2. SMARTLAM demonstrator for “intelligent combination of functionalized” polymer layers.</figcaption></figure>

capabilities of the additive manufacturing capabilities.

In SMARTLAM the following types of functional
elements for printed electronics had been identified
over the first months and are currently subject to
further investigations and discussions with respect to
fulfill the application requirements as well as to meet
the technological constraints:

### Printed electronics

- electrode structures [line, interdigital]

- MR Sensors

- Capacitive switches

- Functional elements for the energy storage

- Printed batteries

- NIL-based Batteries

- Components for electronics

- Resistors

- Switches

### Functional elements for micro fluidics

The concepts allows for a broad range of fluidic
functional elements to be investigated in a more
detail, especially in M7-12.

- Microfluidic channels

- Membranes

- Valves

- Mixers
- Storage

- Actuators

## Functional elements building on surface modification

SMARTLAM technologies basically allow for an active treatment of surface properties (chemical and physical properties). Surface activation (e.g. Ionisation) or an active control of wettability by laser processing are just two examples to mention in this context.

## Composite functional elements

Some of the functional elements can be combined to composite functional elements of a "higher" integration level. The functional element "positioning and integration of a chip" may consist of two functional elements "milling of a pocket" and "e-contacting"

## Implementation strategies

Many of the functional elements mentioned above can be realized in a single manufacturing step, where the function can be realized by manufacturing of a single geometric element, which will be covered in more detail in the next paragraph. In most cases even more complex functional elements can be described as a combination of such features. From a process perspective however, there are typically multiple solution strategies for implementing functional elements. The "Via" functional element may serve as an example, as technological as well as chemical solutions are feasible and will have to be selected depending on the application boundary conditions. These solutions include but are not limited to:

- realisation of a "mechanical" contacting between film layers consisting of a through hole filled with electronic ink.

- Physical realisation of a contacting using the special material properties e.g. of "anisotropic conductive films"

## 2.2 Features

"Features" represent a kind of intermediate between the application-oriented function element and the "manufacturing output", mostly resulting in a set of geometric primitives that can be micro milled or cut, coated, printed, welded, etc.. The following examples may illustrate underlying concept:

- A single hole can be a vertical microfluidic channel as well as a pocket for integration of discrete parts.

- An array of such micro might represent a "micro sieve" for blood separation in the bio disposable application areas.

- A combination of the "hole"-feature with other features such as the filling of a hole with e-ink can result in a contacting for manufacturing of "vias", know from printed circuit board technology

### Typical features:

- Channels (for fluidic or optical properties)

- Pockets (cavities, lumen or locating holes)

- Printed lines (conductive tracks, sensors, "via")

- Material layers with properties, different from polymers (realisation of batteries, realisation of membranes (elastomers)

Evaluation tests could demonstrate the validity of this approach and similar concepts on feature level had been successfully tested in other micro related contexts [3]. A thorough evaluation in order to validate the principles of this concept will be performed over the course of the project.

## 3. Selection of manufacturing process chain and product design

An integrated micro device often consists of a very large number of features which form the application oriented functional elements. For the fabrication of such devices a manufacturing process chain of high complexity is required. To address this problem, in SMARTLAM the product design and the process selection are incorporated into a hierarchical model where decisions are made at different abstraction layers. Similar hierarchical approaches have been elaborated and realised in CIM or STEP [4][5].

### 3.1 Product design method

In the SMARTLAM 3D-I concept the product designer uses a library of structural features which can be integrated to build functional elements. These features together with information about technologies that can be used for their fabrication are stored in a database. In the hierarchical model the first layer is the library and is the only layer open to the designer. The second layer is the pool of available technologies and forms the manufacturing process chain. The third layer is the process parameters and is used for the optimisation and selection of specific process chain (see Figure 4). If the simple example from the previous section is taken, the library will offer a variety of micro holes in a range of sizes and materials which can be arranged to form a micro sieve. Some of the technologies that can be used for the fabrication of wholes in a polymer material are micro milling, laser machining or micro-injection moulding. The process parameters for the machining of the specific holes selected by the designer are stored in the database. After the micro sieve the next functional element on the device might be a conductive line. Possible technologies for its execution would be any kind of lithography, aerosol or jet printing. The design can be continued with the next device feature or a lamination step. Thus it is apparent that an effective method of selecting the best available chain has to be created. The advantage of using a library of preset geometries is that the designer is limited to structures which fabrication is already a well-established process. The number of alternative process depends on the completeness of the database which can be expanded when required. The addition of each new device feature multiplies the number of the possible manufacturing process chains by a factor equal to the number of available technologies for the feature. Therefore the development of fast and effective way of selecting the optimum chain is essential.
<figure><img src="image_6.png" /><figcaption>Fig. 4. SMARTLAM process sequence hierarchies.</figcaption></figure>

## 3.2 Process chain selection method

Large number of the initially identified process chains are rejected by breaking some of the links on the second hierarchical level. This can be done either on material- technology (M-T) or technology- technology (T-T) compatibility criteria. (see Figure 4). The T-T compatibility criterion is relatively simple and normally there is a clear rejection or approval of a specific chain. In many cases this is the inability of combining vacuum with non- vacuum technologies. As an example, laser machining cannot be combined with electron lithography due to the extreme complications of the workpiece transfer. In cases when the technology compatibility assessment is not that straightforward SMARTLAM can exploit the Process Pair Interface Model developed under the EC FP7 funded EUMINAfab project which provides more detailed analysis of the pair maturity level [6]. The M-T criterion is more complicated and requires some more detailed investigation. For many technologies there is a “favourite” material but this does not exclude the use of some other materials. For example PET is one of the most popular substrate materials for aerosol jet printing but shows poor UV laser machinability. This requires the development of a scoring system for different material- technology pairs and setting of threshold score below which the manufacturing chain is rejected.

After applying the compatibility criteria the remaining process chains are arranged in an array:

$$ \mathit{Array} = (\mathit{chain}_1 \dots \mathit{chain}_{i-1} \mathit{chain}_i \mathit{chain}_{i+1} \dots \mathit{chain}_n) $$

Technologies that can be associated with more than one set of process parameters are linked in a

separate chain for each set. The minimisation of the array is executed in two phases. In the first one process parameters such as temperature or pressure are assessed and it is checked whether any of the technologies or materials in the chain imposes restrictions to these parameters. Chains which do not meet these criteria are rejected. The second minimisation phase is when the actual process optimisation is performed. This is done by comparing the process parameters against the user requirements. User requirements can be machining time, cost or accuracy. At the end only the best matching chain remains which is used for the fabrication of the designed device. An advantage of this approach is that the selection of the technologies also serves for identification of the process parameters. This allows for very fast and efficient reconfiguration of the SMARTLAM modules.

## 4. Technologies and materials of relevance for the Smart manufacturing approach

Representing the smallest building blocks in modelling of process chains three different types of technologies are currently under evaluation regarding their integration in the system setup:

- Technologies for additive manufacturing and e-printing aerosol jet printing. In SMARTLAM the e-printing functionality is realized by aerosol jet printing, offering good results for manufacturing of line-based geometries such as conductive paths [8]

- Handling assembly and bonding technologies [7]

- Technologies for direct and indirect milling and cutting of polymer films [laser milling, cutting, nano imprint lithography, hot embossing]
Each of these technical sections will be briefly introduced with respect to its specific relevance for the Smartlam approach.

## 4.1 Structuring Technologies

For (pre-) structuring of films, technologies such as laser direct structuring but also indirect technologies such as NIL or hot embossing are under evaluation. Criteria to be mentioned in this context are scalability of processes, machine unit costs, required precision, small lot sizes vs. larger volumes.

First tests have been conducted at KIT-IAM to evaluate typical SMARTLAM features and functional elements. In SMARTLAM polymers such as polycarbonate (PC) or poly(methyl methacrylate) (PMMA) are used. Those polymers show a high laser beam absorption in the ultraviolet (UV) (248 nm, 193 nm) as well as in the infrared (IR) (10.6µm). From previous studies it is known that a high optical absorption at UV wavelengths leads to low material removal rate, which in turn enables a precise control of the achieved ablation depth and a good surface quality [9]. With UV laser structuring lateral resolutions in the sub-micrometer range via direct writing or direct optical imaging of complex mask structures can be achieved. Furthermore below or in the range of the laser ablation threshold of the polymer a surface modification is possible. With optimized laser and process parameters surface modification can be applied in order to adjust the wettability of polymer surfaces from superhydrophilic to superhydrophobic properties.

<figure><img src="image_7.png" /><figcaption>**Fig. 5** Top Level interconnect design for Chip integration</figcaption></figure>

IR laser structuring of polymers can provide a very flexible material processing with high processing speeds. High accuracy channel widths down to 50 µm can be produced in PMMA. Nevertheless, due to the fact that IR laser-assisted ablation processing is mainly thermally driven, a main challenge is to achieve small structures (<50 µm) with minimized heat affected zone.

An appropriate combination of UV and IR laser processing can be applied for the generation of functionalized polymeric micro devices [10]. Fig. 6 and Fig. 7 show laser structured thin polymer films using IR and UV laser systems.

<figure><img src="image_8.png" /><figcaption>**Fig. 6** Micro channel structures in PMMA achieved by IR laser ablation (wavelength: 10.6 µm)</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>**Fig. 7** Pocket structure in PET achieved by UV excimer laser ablation (wavelength 193 nm)</figcaption></figure>

## 4.2 Polymer film handling and assembly related technologies

The polymer film handling addresses a limiting aspect with respect to the achievable precision: the handling and (fine) positioning of parts within the systems. Other technologies such as dispensing and bonding of polymer films are subject to a detailed analysis as well. While there exists a long experience in handling of polymer films the proper alignment of the sheet layers with respect to the required accuracy of a few µm is still challenging. Manufacturers have to deal with selective thermobonding to address the relaxation behaviour of the film material without loss in accuracy.

The polymer film handling process is shown in Fig. 8. The first step, feeding, supplies singular film sheets. This is challenging, as the films require to be provided as flat as possible for the precision pick and place process and have to be “loose” in order for the gripper to grab it. A magazine with an air suction for each sheet could be a possible approach.

<figure><img src="image_10.png" /><figcaption>**Fig. 8** Polymer film handling process</figcaption></figure>

The second process step is gripping. As the film sheets are flexible, but still have to be precisely positioned, a uniform suction over the whole sheet area is pursued. Deformations during the gripping process have to be avoided at any cost, as these would lead to major deviations between the respective product layers. A flat vacuum gripper with an arrangement of holes <<1mm could be a possible approach.

The third step is the positioning of the sheet relative to the substrate. This requires positioning in position (x, y, z) and orientation (φ). The required precision depends on the type of layer. If the sheet features micro-structures, which require relative alignment to the substrate, the required positioning accuracy might be <25µm. If the sheet does not
feature any micro-structures, the positioning accuracy
is rather uncritical. A cartesian precision placement
system with an additional rotational axis is proposed
here.

Letting the sheet go is as critical and challenging
as the gripping process. While it is very important to
attach the sheet as uniformly as possible without any
deformation, no deformation may happen during the
disengagement. At the same time neither substrate
nor sheet may be damaged during disengagement. A
possible strategy could be a light blow-off of the
sheet.

For the joining process several options exist,
such as adhesive bonding, induction welding, laser
welding, lamination or thermobonding [14]. The
requirements to be addressed are joining of the sheet
with the substrate without deformation, damage and
voiding. Currently, a lamination process is
investigated, as it seems to fit very well to the
requirement profile.

For the integration of the functional elements
"integration of discrete part" and the related
technologies "milling of a pocket", "dispensing of
glue" and "positioning of chip" first tests had been
conducted to evaluate the feasibility.

The "milling of a pocket" is done by application of
the above-mentioned structuring technologies. The
further technologies are merged to a discrete part
assembly process. For the functional element
"integration of discrete part" first tests have been
carried out with a top level interconnect design for
chip integration (see Fig. 5.)

The chips have to be fixed in the cavities with
adhesive bonding. In addition, the dispensed
adhesive has to fulfill another important function: It
works as a convex or concave bridge filling the gap
between the LED and the substrate, on which
electrical circuits can be printed. Furthermore the
adhesive has to protect the chip to ensure reliability
during operation. The length of the chips edge is
smaller than 500 µm. The corresponding pockets are
slightly larger. Therefore the amount of adhesive is in
the low nanolitre range and has thus to be dispensed
very precisely. Furthermore adhesive forces between
the walls of the pocket and the adhesive disturb the
accurate and repeatable positioning of the droplet. To
still achieve a stable assembly process, high
precision measuring equipment for the lateral and
vertical dimensions of the pockets and the dispensed
adhesive as well as a precision placement system
with a positioning accuracy in the low micron range
for the dispensing tool is required. The same high
requirements have to be fulfilled for the chip
placement. Fig. 9 shows optical measurements of
three stages of the chip assembly process: at first the
empty pocket is filled with adhesive and the
assembled chips with the adhesive bridge. Afterwards
the adhesive needs to be cured. The products
assembled within SMARTLAM are based on polymer
films. Currently a broad range of substrate materials
is intended to be applied, e. g. polyethylene
terephthalate (PET), polycarbonate (PC) or
poly(methyl methacrylate) (PMMA). The glass
transition temperatures (PET: 70 °C; PC: 145 °C;
PMMA: 105 °C) should not be exceeded during the
curing of the adhesive. For most common adhesives
comparative high temperatures above 100 °C are
needed for fast curing. To maintain low cycle times

<figure><img src="image_11.png" /><figcaption>Fig. 9 Stages of chip assembly</figcaption></figure>

with low temperatures UV curing adhesives are taken
into account. Laser as part of the SMARTLAM
system could potentially be used for precise and local
curing to reduce the heat-affected zone compared to
a convection oven.

The SMARTLAM e-printing functionality is used
in a following step for the electrical connection of the
chips.

## 4.3 Materials properties of specific relevance for SMARTLAM concept

Novel polymer film with advanced material
properties are of a specific interest for the
SMARTLAM approach. There exists a broad range of
material features that will become of interest for
SMARTLAM applications:

### "Standard materials"

The use of polymer materials with dedicated optical
and mechanical properties provides opportunities for
a broad range of applications but does also cause
problems while its application in the SMARTLAM
context. While the activities in the startup phase are
focussing on polymer films, the application of ceramic
films, similar to LTCC applications [15] as well as the
application of flexible glass [16] but also
combinations of different substrate layers with
surface properties will be subject to the future
research.

In addition materials with advanced chemical and
physical properties will be evaluated in later stage of
the project. As an outlook may serve the following
materials:

- Anisotropic conductive films allowing for the an
electrical conductivity vertical to the sheet plane,
While the application in LCD panel production
and chip industry is well established the
application of the ACF in flexible environment is
still subject to research activities, e.g. in the field
of flip-chip on flex packages assembly [11]

- high optical transparency, robust flexibility, and
excellent conductivity caused by general
synthesis of aligned carbon nanotube/polymer
composite films with. (potential applications
such as flexible conductors for optoelectronic
devices) [12]

- Actuation of the microsystem, caused by electro
active properties of the polymer [13]
## 4.4 System integration on process chain level

According to the 3D-integration paradigm different combinations of process sequences -each representing the respective process sequences for manufacturing of the respective design building blocks. Figure 10 provides an example how such process sequences could look like

<figure><img src="image_12.png" /><figcaption>Fig. 10 Example of a process sequence for connecting a discrete part</figcaption></figure>

Different setups are currently under evaluation and testing, contributing to the decision support tools as well as the database.

# 5. Conclusions and Outlook

In the paper a novel approach for flexible scalable manufacturing of micro components building on a combination of laminated objects modelling, integration of laser technologies for structuring of films and printed electronics for e-contacting and printing of electronic components was presented.

Specific attention was paid to the design of applications, building on a new approach for 3D-integration, (3D-I). Design elements on different aggregation levels and their implementation have been introduced.

Over the next month these concepts will be developed further and adapted to the needs of the two project demonstrators in the field of lighting and microfluidics

## Acknowledgements

The research related to the SMARTLAM flexible scalable manufacturing approach receives funding from the European Community's Seventh Framework Programme (FP7/2007-2013) Grant agreement No. 314580.

Finally, the support by the Karlsruhe Nano Micro Facility (KNMF, www.kit.edu/knmf) for laser processing is gratefully acknowledged.

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