Two-shot molding process

Figure 7-30. Du Font s Ary Ion polyary late and Rynite TP-polyester resins eliminate parts and simplify assembly of Xetec Corp. s three-dimensional circuitboard for lighting ballasts. A special two-shot molding process removes the need for metal fabrication and yields a low-cost, reliable component for use in rapid-start fluorescent lighting ballasts.

The two-shot molding process chain is very short. As Fig. 3.18 shows, the interconnect device is produced in a sequence of two molding cycles prior to metallization of the electrically conductive structures. In this process the conductor layout is defined in the molding stage. 

Electrical properties Automotive engineering is one of many areas of application that place high requirements on the product s electrical properties. KARTING provides guide values for resistivity, dielectric strength, current-carrying capability, and so on and indicates the standards and tests that the two-shot molding process has to satisfy. 

Co-injection molding involves injecting two or more different materials into a mold, generally in sequence. To accomplish this, molding machines are fitted with multiple injection units (Figure 14-53). Two-shot molding, the most common version, often utilizes an indexing mold. In this process, the mold is rotated 180° after the first shot fills a portion of the cavity, then the second shot finishes the part... 

This chapter presents an overview of performance plastic polymers in commercial planar and 3-dimensional circuit board products, and describes in detail one approach (two-shot molding) developed as an integrated 3-D circuit manufacturing technology. The distinctions between conventional planar (2-dimensional) circuitry, based on thermoset laminates and "subtractive etching processes, and the enhanced design flexibility afforded by expanded interconnection capacity in three axes are discussed. Specific examples of 3-dimensional interconnect protoypes and products are described and pictured. 

The unique attributes of "catalyzed resins are that they eliminate the need for secondary (after molding) pre-plate activation or "seeding" operations common to conventional plating-on-plastics (POP) processes. For molded circuit board manufacture, catalytic resins are used in two-shot (two-component) molding processes which form highly complex 3D plastic structures which are capable of being selectively plated without the need for plating masks or resists. Polymers currently available in a "catalytic" composition include only amorphous sulfone and imide based systems. 

MOLDING/METALLIZATION. Molded thermoplastic circuit board substrates may be rendered selectively conductive by several additive process techniques including conductive polymeric thick film inks (PTF), and semi and fully additive electroless/electrolytic platings. Of the various chemical process methods developed to produce circuitry on a molded plastic substrate, one method practiced by Pathtek, A Kodak Company, combines both "catalytic" and "non-catalytic" resins in a highly automated commercialized two-shot molding/selective metallization process. 

The expressions also used for this process are bicomponent injection, coinjection, or two-shot molding. When a plastic part, previously molded in a specific mold, is introdnced in another mold, in the same way as a metal insert, and a different plastic is molded over it, the expression overinjection is sometimes nsed. 

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. 

In the past, two-shot molding or two-shot injection molding generally referred to a process in which a first shot of material is subsequently enclosed within a second shot. In MID technology, however, the process is one in which the second-shot plastic compound is applied on top of the first shot. In the course of time two main versions of this basic process have established themselves for MID technology [48] ... 

Broadly speaking, there are two basic processes for two-shot molding. They are the PCK process (printed circuit board Kollmorgen), in which the two shots are molded directly one after the other, and the SKW (Sankyo Kasei wiring board) process, in which the plateable component is chemically catalyzed before the second shot is molded [48,126]. 

Etching is followed by seeding with palladium. The palladium nuclei are inserted into the exposed cavities and are catalytically active in the follow-up chemically reductive metallization process. The plastics used in two-shot molding are generally core-catalytic and require no additional seeding or activation. Only the surface has to be etched open to permit access to the catalysts embedded in the plastic [30]. 

The pressure sensor is a two-shot molding. Production volume is on the high side of 10 million units per year. The printed-circuit board is contacted on the MID by conductive-adhesive gluing (isotropic conductive adhesive). Nonconductive adhesive is also applied for mechanical location. The contact pins of the MID are tiny bumps to which the conductive adhesive is applied in the dispensing process. [143]... 

Another way of looking at the two-shot process is to consider the technique to be a derivation of metal insert molding except that the first shot is plastic rather than a stamped or formed metal. 

Figure 5. Two-Shot Process First shot molded insert.

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