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Wednesday, 30 April 2008 19:00
Technical Abstracts PCB Design

“Changing the Methodology for DfM, Moving from Design-Checker to Interactive, Informed Design Methodologies”

Author: Nolan Johnson; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Abstract: “Design for manufacture” strongly implies the use of manufacturing information while making design decisions; in other words, incorporating manufacturing knowledge during initial design. Most available DfM tools don’t fit into the design workflow until the PCB design is already complete. There are three nasty consequences to the current approach:

1. Designers are forced to make under-informed design decisions during layout, when DfM is easiest and least expensive to design into the project.

2. When DfM errors are inevitably identified, they require significant rework, engineering effort and cost.

3. Added rework to fix backend batch DfM increases risk of missing the market window.

New DfM approaches don’t postpone checks until the end of the design. The methodology described here enables designers to be notified (almost interactively) of any manufacturability issues as they design. By attending to DfM issues from the onset, designers are not only able to “pass” DfM, but also can invest in optimizing the manufacturability of the design, even from the first prototype.

This paper presents case studies and efficiency results from the implementation of an interactive DfM model to support manufacturing. (IPC Apex, April 2008)

Solderless Assembly

“Development Status of an Occam Electronic Assembly Method”

Authors: Edward S. Binkley, Ph.D. and Richard F. Otte; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Abstract: The Occam assembly concept is under development as a low-cost, solderless assembly method. This version of the process uses a “sticky” surface to hold conventional SMT parts in place until they can be covered with an encapsulant and restrained by a containment frame that permanently holds them in place. Major conclusions drawn from the effort to date include: The pros and cons of the process are highly dependent on the product to be built; Occam can yield lower costs, especially for simple, low part count products when a final product results from the process; costs are reduced by eliminating fabrication, eliminating some hand assembly, potentially eliminating a final enclosure, and through use of lower temperature parts. Work on materials and the process is needed to find combinations that work well together so the promise of the process can be realized. (SMTA Pan Pac Symposium, January 2008)

Thermal Interface Materials

“Full Metal TIMs”

Author: Ross Bernston; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Abstract: Soft metals can be compressed between the two surfaces of a thermal interface to create a TIM with very low resistance. Generally, this type of interface requires pressures of several hundred pounds per square inch or more to conform to the contact surfaces. With a room temperature tensile strength of only 270 psi (six times softer than lead), indium metal and alloys are well suited to lower-pressure applications.

It is important to note when pressed against a rough surface, a metal TIM conforms to the highest (microscopic) peaks. The harder material mechanically embeds into the softer material, resulting in intimate contact over that area. When the materials in contact are metals, the electrical and thermal contact is enhanced by the shared electrons. The plastic deformation exposes a fresh metal surface, resulting in a “metallurgical” bond over that region. Metal TIMs offer substantially higher thermal conductivity than other commercial TIMs. With this high conductivity, these metal TIMs offer the lowest thermal interface resistance, enabling design of higher power and smaller electronic devices. The high conductivity translates to less sensitivity to bond line thicknesses and coplanarity issues than polymeric TIMs. (SMTA Pan Pac Symposium, January 2008)

Circuits Assembly provides abstracts of papers from recent industry conferences and company white papers. With the amount of information increasing, our goal is to provide an added opportunity for readers to keep abreast of technology and business trends.

 

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