The trend that has been dominating electronic and mechatronic products for many years is clear: components must get smaller in size, while packing in more functions. Also, in order to maintain their market positions, manufacturers in the communications technology sector are under tremendous pressure to continuously launch new products in shorter intervals, while still making them stand out from the crowd. Technologies such as 3D Molded Interconnect Devices (MID) enable new products to be produced with unprecedented functionality. In particular, LPKF’s Laser Direct Structuring (LDS) technology offers the benefits of reliable, efficient and productive technology, with the added advantages of economic prototyping processes and a short production lead time.
The technology’s current main application is the production of smartphone antennas, but significant growth in tablet or laptop antennas as well as new applications in the automotive and medical fields are expected. For the handset business, LDS offers the opportunity to minimize the footprint of the radiator by integrating it directly on the carrier, which negates assembly steps and enables several antennas to be integrated on the same carrier. To improve RF performance, it is also possible to place the antennas either on the covers, middle decks or on both sides of a component, depending on the intended RF and mechanical properties.
The flexibility and design freedom that comes with utilizing full 3D enables manufacturers to easily tune the antennas during the design and build process. All radiator areas, especially the RF tuning areas, can be easily modified during the pre-production stages, leading to short lead times. Approximately 40 percent of high level smartphones come with at least one LDS component. Figure 11 illustrates the differentiation of the use of LDS systems by market segments.
MID is all about integrating electronic circuits and components directly on three-dimensional plastic components. This enables chips to be elegantly stacked in their assemblies, and the antennas in smartphones or netbooks to be incorporated directly within the housing, thus saving space. Integrating functions also decreases the number of individual components required, eliminates a whole range of production steps, automatically saves additional costs and creates higher quality components.
The LDS method (patented by LPKF) provides significant advantages, both technically and economically, over common methods for integrating electronic circuits directly on plastic components. It uses a thermoplastic polymer doped with a laser-activatable metal-polymer additive. When the laser beam hits this polymer it activates the metal complex and creates a precise track with a roughened up surface.
Exposed metal particles that are created in the process form the nuclei for the subsequent metal coating process. The laser beam therefore draws the structures required on the component so that the conductor layers are created precisely along these tracks in an electroless metal coating bath. Copper, nickel and gold finishes can be applied with this method.
The special attributes of lasers such as high flexibility, speed, resolution and precision, work to their strengths in this process. If the circuit has to be reconfigured, all that is needed is a new set of control data to be fed into the laser unit. This means that one basic component can be used to create a range of parts with different functions merely by changing the design of the circuits drawn by the laser beam. And because the control data can also be changed during production, companies can produce small and medium-sized series and even one-off products cost efficiently.
With regards to materials, the main prerequisite is that the metal oxide containing the LDS additive has to be evenly distributed and sufficiently concentrated in the thermoplast. Most of the leading plastic manufacturers offer LDS versions of their thermoplastics. The spectrum consists of amorphous and partially crystalline polymers whose thermal stability ranges from standard to high temperature thermoplastic. These include numerous types of materials that are suitable for lead-free soldering.
In the past, LDS plastics were black because the LDS additives were inherently black, but this has changed recently with SABIC and Mitsubishi Engineering Plastics offering LDS materials that can be adapted to nearly any customer need using pigments. Figure 2 shows the colorful world of LDS using Xantar LDS from Mitsubishi Engineering Plastics.
Between the layout of a MID part and series production there are several prototype stages. Up until now prototyping and low volume production has either been expensive or impossible. In generative manufacturing, processed parts are generated layer-by-layer directly from CAD data and without the use of forming tools. The most important procedures are Fused Deposition Modeling (FDM), Selective Laser Sintering (SLS) and Stereolithography (SLA). The range of plastics available for the different process technologies is expanding. In this way, developers obtain MID prototypes whose characteristics are iteratively optimized for later use.
LDS prototyping is based on a special paint that is used to coat a surface of a plastic body created by rapid prototyping. ProtoPaint LDS incorporates laser activatable additives, enabling almost any plastic surface to be treated with a laser-activatable coating. It is currently available as a primer and hardener, but a one-component version is planned that can be applied using a simple spray can.
For painting, first a blank is made and coated with a layer thickness of about 30 to 40 µm. In practice, two or three consecutive finishes are ideal for a homogeneous layer. Later this component can be structured like any LDS series part. The adhesive strength of the conductors after metallization is similar to plastic components made of LDS plastic. After the building up of a body in rapid prototyping, the painting is carried out. The laser transmits the projected circuit structures, metal layers being built up in an electroless bath. The process is shown in Figure 3.
The last step in the prototyping process is to metallize the plastic parts. In collaboration with Enthone GmbH, LPKF has developed a very simple solution: LPKF ProtoPlate LDS is a copper bath that can be used without chemical expertise. The copper chemistry is put into a beaker and heated up to approximately 45°C; the activator is then added and the structured parts put into the bath. It is active for approximately two hours and can build up copper layers between 3 and 10 µm.
The fully developed prototyping process closes the gap between layout and series production in an effective way. It becomes easy, fast and economical using the same technology as the mass production.
MID Survey 2011, 3D-MID e.V., Germany, Nuremberg 2011, www.3dmid.de.