LPKF-LDS Process
2-component injection molding and hot stamping are already used to manufacture MIDs (Molded Interconnect Device). Both of these methods are tied to product-specific tools to create a circuit on the component.
The associated high initial manufacturing costs considerably limit the efficiency of these methods for small production runs and design modifications. Prototyping shortly before series production is almost impossible.
Moreover, increasing miniaturization of the circuits on MID components leads to a considerable rise in tooling-up time and expense. The LDS (Laser Direct Structuring) method is a flexible and economic alternative. The LPKF-LDS process consists of the following steps:
Material Selection
A number of series materials or thermoplastics are available to produce injection-molded MIDs for the LPKF-LDS method. These materials are suitable for a large number of different applications thanks to their broad spectrum of properties:
PA6/6T (semi-aromatic polyamide)
- Very high thermal shape stability, suitable for reflow soldering (also with lead-free solder)
- Very good mechanical properties
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Thermoplastic polyester (PBT, PET and blends)
- Very good mechanical and electrical properties
- Very high thermal shape stability with addition of PET
Crosslinked PBT (polybutylenterephathalate)
- Migration-resistant fire protection equipment (VO - 0.4 mm after UL94)
- Irradiation crosslinkable for high temperature resistance (all soldering processes)
LCP (Liquid Crystal Polymer)
- Very good flow properties
- Very good dimensional stability under thermal stress
PC/ABS (polycarbonate / acrylnitrile / butadiene / styrol)
- Very good surface properties
- Very good mechanical properties
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Injection Molding
2-component injection molding and hot stamping are already used to manufacture MIDs (Molded Interconnect Device). Both of these methods are tied to product-specific tools to create a circuit on the component.. |
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Laser Activation
The laser-activatable thermoplastic has a special additive in the form of an organic metal complex, which is activated by a physico-chemical reaction induced by the focused laser beam. This cracks open the complex compounds in the doped plastic, and breaks off the metal atoms from the organic ligands. These act as nuclei for reductive copper coating.
In addition to activation, the laser also creates a microscopically irregular surface. The laser only ablates the polymer matrix, not the fillers added to the plastic. This creates microscopic pits and undercuts in which the copper is firmly anchored during metallization. |
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Laser Activation
The metallization part of the LPKF-LDS process begins with a cleaning step to remove laser debris. This is followed by additive build-up of the tracks with the help of current-free Cu baths.
An advantage of this procedure is that it dispenses with preliminary activation steps. Baths of this type typically deposit 3 – 5 µm/h. If a greater thickness of copper is required, this is achieved using standard electroforming Cu baths. Application-specific coatings such as Ni, Au, Sn, Sn/Pb, AG, AG/PD, etc., can also be created.
AssemblingA number of laser-activatable plastics with high degrees of thermal shape stability, such as PA6/6T, LCP and irradiation cross-linked PBT are reflow solderable and therefore compatible with standard SMT processes.
Solder can be applied using stencil printing. However, this is only possible with flat surfaces at the same level. Dispensing should ideally be used if different heights are required or solder is to be applied in cavities.
The same applies to assembling SMD components. If all of the components are at the same level, automatic assembly can be carried out using standard automatic placement devices. Raised surfaces can only be automatically assembled if the pick-and-placer has a z-axis. Automatic assembly is more complicated on slopes or free-form surfaces which usually have to be assembled manually.
In addition to the assembly of SMD components, MIDs manufactured using the LPKF-LDS method are also suitable for chip contacting methods such as bonding. Bond connections are made using thick aluminum wire, or thick/thin gold wire with e.g. 25 µm diameter.
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