Who's this issue's expert?Q: I am producing multilayer PWB's for a variety of backplane and mother board applications and have recently been advised of a requirement for boards to be built using lead-free solder. Should I be concerned about Tg, Decomposition temperature or both as I fab these boards? A: These are very different properties and need to be considered individually. Glass Transition Temperature The glass transition temperature is the temperature below which the physical properties of amorphous materials vary in a manner similar to those of a solid phase (glassy state), and above which amorphous materials behave like liquids (rubbery state). (Tg) is related to molecular free volume. A resin system exhibits changes in physical properties, such as an increase in the rate of Z direction expansion. Because Z-direction expansion impacts plated through hole reliability in PWB (Printed Wiring Board) An alternate term for printed circuit board. See printed circuit board. fab and subsequent assembly processes TMA TMA Turnaround Management Association TMA Texas Medical Association TMA Transportation Management Association TMA Training and Management Assistance (a component of OHRD, which is a component of OWR) TMA Tooling & Manufacturing Association is often used to characterize Tg. On the other hand, Decomposition Temperature (Td) is that temperature at which chemical bonds in the resin system actually start to break, resulting in emission of gaseous components. Weight loss measured by TGA See TARGA. TGA - Targa Graphics Adaptor is the standard method of determining Td. For your application you may want to try a High Tg multifunctional epoxy system such as Arlon's 45N (Tg 170[degrees]C. Td 295[degrees]C. For very high layer count builds a higher Tg material such as polyimide Pronounced "poly-ih-mid." A type of plastic (a synthetic polymeric resin) originally developed by DuPont that is very durable, easy to machine and can handle very high temperatures. Polyimide is also highly insulative and does not contaminate its surroundings (does not outgas). might be desirable, especially if PTH PTH abbr. parathyroid hormone Parathyroid hormone (PTH) A chemical substance produced by the parathyroid glands. This hormone is a major element in regulating calcium in the body. reliability is critical. Arlon's 35N polyimide (Tg 250[degrees]C, Td 361[degrees]C) with a total Z expansion from room temperature to 250[degrees]C of only 1.1% is an optimal material for high temp process and end use application. Newer products such as Arlon's 210[degrees]C Tg 11N. a chemically modified epoxy system originally designed for the Burn-In industry may also be of interest. For additional information about Arlon solutions to with you temperature or stability problems, contact your Arlon sales or technical service representative or call Arlon directly at (909) 987-9533. Have A question: email us at experts1@arlon-med.com Speak with an Arlon Laminate laminate, n a thin slice of porcelain or plastic fabricated in a dental lab, which is cemented to the front of the teeth to cover gaps, whiten stained teeth, or reshape chipped or broken teeth. EXPERT at CPCA--Booth # B159 Chet Guiles, Technical Consultant |
|
||||||||||||||
Printer friendly
Cite/link
Email
Feedback
Reader Opinion