Laser direct structuring

The substance and significance of the thermal expansion of plastics is discussed in more detail below. The reason is that MID are multimaterial systems, consisting of polymer substrate (thermoplastic, and in the future thermoset plastics as well), metal (e.g., Cu-Ni-Au), and electronic devices. Fig. 2.7 illustrates this, taking an MID conductor structured by laser direct structuring by way of example. 

FIGURE 2.7 Microscope image of a laser direct structured, wet-chemically metallized Cu/Ni/Au conductor on a PET/PBT blend... 

The following sections set out the purely materials-related and tool-related prerequisites for the two processes now most commonly used in MID production two-shot molding and laser direct structuring (LDS). Chapter 3 of this book deals in depth with the workflows, possibilities, and boundary conditions associated with these manufacturing processes. It also contains information about the production methods such as hot embossing and film insert molding, neither of which is considered in more detail here from the materials point of view. 

Laser direct structuring is based on the notion of laser activation of specially additivated plastics. The additives that enable the LDS process and that are finely distributed in the MID basic body are transformed into catalytically effective species during laser structuring and must satisfy different requirements [6] ... 

The laser direct structuring process developed by LPKF can produce high-resolution circuit layouts on complex three-dimensional interconnect-device structures in a multistep process sequence. 

TABLE 2.4 Important Properties of Thermoplastics Suitable for Laser Direct Structuring [7, 22, 147]... 

The main laser-structuring techniques for MID are derivatives from the world of printed-circuit board engineering. For this reason the various techniques are commonly classified as additive, semiadditive, or subtractive. Laser direct structuring is an additive technique, and its most important manifestations are LPKF-LDS and ADDIMID. MIPTEC, a process developed by Panasonic, is one of the semiadditive techniques. Subtractive laser structuring techniques are commonly used on ceramic substrate materials. Figure 3.2 is an overview of the individual structuring techniques and the steps involved. 

It is also possible to prepare plastics for laser direct structuring without the specific LDS additive. LPKF has a product akin to an LDS painting system for this purpose. ProtoPaint LDS is a two-component primer/curing agent system for coating plastic injection moldings with an LDS-compatible skin. Application is by standard spray gun or with a recently developed and more user-friendly aerosol. A coat approximately 30 to 40 pm thick has to be applied in two steps and then cured. The plastic parts prepared in this way can then be structured the results are comparable to those achieved with LDS plastics. This process, however, is intended primarily for prototyping because the constant-use properties are not comparable with those of plastics with LDS additive in the compound [15]. 

Nothing definite can be said as yet about the structure widths of conductor traces and spacing. Research to date has focused primarily on reproducible laser direct structuring in combination with adequate mechanical bonding strength of the chemical metallization. In this context, too, very promising results have been obtained. They are dealt with in more detail in Section 3.1.4.3. 

Standard materials In electronic production MID substrate materials for laser direct structuring ... 

Heat-assisted die embossing and CO2 snow jetting are smoothing processes that can be applied to reduce roughness. Plating with average roughness < 10 pm can also be produced on laser direct structured MID. [185]... 

Plastic bodies made by FDM using a suitable LDS material can be laser direct structured. Successful tests have been carried out with PC and PC-ABS [120]. The support materials necessary for the FDM process do not have any negative effect on LDS. The geometric surface structure of the FDM parts, however, can restrict the possible areas of application. Tests of the FDM process using a PBT modified with an LDS additive have shown that, because of the wavy surface structure, an extra smoothing step has to be inserted prior to the LDS operation [134,186). 

Ingo Kaiser s systematic approach affords a guideline for the entire MID development process. Integrative development from product and production system is taken into consideration equally with the interdisciplinary reach of the development project. As regards the elaboration of specifics, however, his approach is limited to laser direct structuring. 

Is the selected MID process (e.g., laser direct structuring) still suitable for manufacture of this interconnect device (e.g., regarding three-dimensionality and conductor width) ... 

Laser direct structuring The design guideline for LPKF laser direct structuring is also subdivided in the same way. The information is based on the machines and tools used in the company and on knowledge acquired in the implementation of various applications. It does not differ in any significant way from the LDS MID guideline issued by the LPKF company, so it not discussed in more detail here. 

The LPKF design guideline provides a very detailed and user-friendly overview of all the processes associated with the LPKF-LDS method. The design rules and parameters for the laser direct structuring process itself are dealt with in detail in Chapter 3. 

The 3D-MID Is manufactured by laser direct structuring. The thermal membrane flow sensor (MEMS chip) is ideal for measuring minute pressure differentials... 

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