Conformity Magazine - December 2008 - (Page 37)

robot. The paint robot offers advantages over manual spray methods, especially in higher volume applications where cost is critical. In the robot, the spray pattern can be programmed and frozen to apply the optimal amount of conductive paint across the entire shielded surface. Manual paint application typically has lower set-up cost than robotic painting, and is a good match with lower volume applications. Table 3 summarizes compatible resins with conductive paint. Difficult to paint resins will usually require primer or other surface preparation prior to the conductive paint process. Part Design Considerations As with resin selection, plastic part design is critical to successful application. There are design approaches that should be avoided if possible, as noted in Table 4. Secondary Processes Inserts can be molded into the part or installed by heat staking or ultrasonic insertion prior to or after plating. If specifying 100 micro-inches (2.5 µm), or if applying conductive paint, inserts should be installed prior to coating process, and masked during the plating operation with a plug or screw to prevent coating being deposited onto the threads. Brass inserts are compatible with plating processes and conductive paint. Gaskets for environmental or EMI/RFI seal are installed after plating or painting. Form-in-place gaskets, comprised of silicone with metal particle filler, can be dispensed around perimeter of compartments of plastic part (or metal part) to prevent interference within the device, and/or around the perimeter of the enclosure to provide an EMI seal from the external environment. The metal particles in the form-in-place gasket material are silver-plated copper, silver-plated nickel or silver-plated aluminum. To minimize risk of galvanic corrosion between the coating and the gasket, it is recommended to match the form-in-place metal with the coating, that is, use copper-based form-in-place gasket material on copper painted applications, and nickel where the form-in-place gasket is being dispensed onto nickel plated or silver painted parts. Form-in-place gaskets range in size from 0.016” (0.4 mm) height to 0.100” (2.5 mm), although it is recommended that gasket height be limited to 0.040” (1.0 mm). Form-in-place gaskets have shore hardness of 40-60 and are designed for approximately 50% compression in the assembled application. They can be dispensed into grooves or onto flat rails and surfaces. Specifying the coating system includes the following elements: • Thickness is usually defined as a minimum. If required, due to part function or fit, plating can be specified as a thickness range. Common Paintable Resins Acrylonitrile Butadiene Styrene (ABS) PC/PBT (Xenoy) Polyphthalamide (PPA) Polybutylene Terephthalate (PBT) Polycarbonate (PC) PC/ABS Blend Poly Aryl Amide Nylon Polystyrene (PS) Polyphenylene Oxide (PPO) Polyether Imide (PEI) Polyphthalamide (PPA) Difficult to Paint Resins (May Require Primer) Polypropylene Polyimide Polyethylene Teﬂon (PTFE) Liquid Crystal Polymer PEEK Table 3: Common paintable resins Plating Design Issues Design Don’t Design Alternative 5-sided box or cup design that can trap air and/or drag out plating Include drain holes, or design part to prevent entrapment of air or chemicals, impacting plating quality and cost plating solution. Tight crevices that can trap plating solution Small blind holes can trap plating solution that can later weep out and damage the plating. Painting Design Issues Design Don’t Difficult to paint tight bosses, crevices and holes due to line-of-sight process to apply paint Table 4: Part design considerations DeCember 2008 Conformity 37 Eliminate crevices in the design or include drain hole Utilize through-holes if possible. If blind holes are required, they can be plugged to prevent plating solution entrapment. Design Alternative Eliminate crevices and small holes that require coating

Table of Contents Feed for the Digital Edition of Conformity Magazine - December 2008

Conformity Magazine - December 2008 Contents Editor's Note FCC Warns Regulatory Fee Payers About Potential "Phishing" Commission Prowls the Web to Enforce Its Regulations First DTV Rollout Initiated in Wilmington, NC New Standards List Released for the EU's Directive on the Safety of Toys ESD Association Call for Papers ESDA. JEDEC Announce Standards Development Cooperation Commission Releases Data on Local Telephone Competition The Future of ESD Testing ESD Open Forum Emerging Issues in Standards: China RoHS: One Year and Counting Challenges in Testing: Revisiting 10-Meter and 3-Meter Radiated Emission Measurements Design Fundamentals: Meeting the Shielding Challenges of Injection-Molded Plastics Focus On...Microwave Absorbers Buyer's Guide FDA Recalls Automated External Defibrillators FDA Revises Guidance on Medical Device Tracking Guidance Document Safety of Passive Implants Released FDA Offers Guidance on Marketing Diagnostic Ultrasound Systems EU Commission Issues Correction on Machinery Directive Standards Other CPSC Actions in the News Product Reviews IEC Standards Update UL Standards Update Looking Back: Items from Past Issues of Conformity Advertisers

Conformity Magazine - December 2008

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