Base Materials

“A Combination Flame Retardant Curing Agent Material for Non-Halogen PCB Laminates”

Authors: Larry D. Timberlake, Ph.D., Mark V. Hanson, Ph.D., Kenneth Bol, and Subramaniam Narayan, Ph.D.; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .
Abstract: With respect to developing “greener” electronics materials, one option available to the formulator is to use compounds that are reactive so they will become part of the cross-linked laminate matrix when cured. A well-understood example for doing this is to develop laminate formulations for epoxy resin systems that incorporate the flame retardant tetrabromobisphenol A, since it is completely reacted into the system. The advantages of using a reactive system can also be achieved with certain non-halogen flame retardants, such as the curing agent studied here. These types of reactive systems also become part of the cross-linked laminate matrix. This new flame retardant material was developed as a reactive phosphorus-containing flame-retardant curing agent with very high thermal and hydrolytic stability. It is intended for use in conjunction with epoxy resin formulations in use today. This paper describes development of this flame retardant and its performance in laminates with comparison to some existing non-halogen systems. (IPC Apex/Expo, April 2011)

Conductor Printing

“Synthesis and Characterization of Low Temperature Sn Nanoparticles for the Fabrication of Highly Conductive Ink”

Authors: Yun Hwan Jo, Inyu Jung, Chung Seok Choi, Inyoung Kim and Hyuck Mo Lee; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .
Abstract: To fabricate a low cost, highly conductive ink for inkjet printing, the authors synthesized a gram scale of uniformly sized tin nanoparticles by using a modified polyol process and observed a significant size-dependent melting temperature depression from 234.1°C for bulk tin into 177.3°C for 11.3 nm tin nanoparticles. A 20 wt% of tin nanoparticles was dispersed in the 50% ethylene glycol: 50% isopropyl alcohol mixed solvent for the appropriate viscosity (11.6 cP) and surface tension (32 dyn cm−1). To improve the electrical property, we applied the surface treatments of hydrogen reduction and plasma ashing. The two treatments had the effect of diminishing the sheet resistance from 1 kΩ/sq to 50 Ω/sq. In addition, conductive patterns (1 × 1 cm) were successfully drawn on the Si wafer using an inkjet printing instrument with conductive tin ink. The maximum resistivity for an hour of sintering at 250°C was 64.27 µΩ cm, which is six times higher than the bulk tin resistivity (10.1 µΩ cm) (Nanotechnology, no. 22 June 3, 2011)

Conformal Coating

“A New Method for Measuring Conformal Coating Adhesion”

Authors: Dr. Christopher Hunt and Ling Zou; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .
Abstract: Coating adhesion has been a difficult property to measure, and industry has made do with a scratch test capable only of qualitative tests. NPL with industrial partners have developed a tape peel test that can be applied to the PCB or component surface. The choice of tape is critical in achieving complete wetting of the fabric, and good adhesion to the coating. The tape is applied with liquid coating to the substrate, and then cured, leaving a flying unbonded section for clamping on during the pull test. The method shows clear differences in adhesion between different coating types: acrylics, polyurethanes and silicones. The effect on coating adhesion of surface cleanliness and the cure state of the resist were investigated. Coatings were generally observed to perform well with these problems. However, coating adhesion to components and some resists proved much more variable, with some coatings failing to adhere to problematic components. Surface energy measurements using a wetting angle technique were also used and compared with the peel data. (IPC Apex/Expo, April 2011)

Soldering

“Investigation for Use of ‘Pin in Paste’ Reflow Process with Combination of Solder Preforms to Eliminate Wave Soldering”

Authors: Guhan Subbarayan, Scott Priore, Paul Koep, Scott Lewin and Rahul Raut, Sundar Sethuraman; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .
Abstract: Pin-in-paste technology is the process of soldering through-hole components using SMT reflow. PiP offers several advantages compared to traditional wave soldering. A primary advantage is the elimination of the wave soldering process and its associated tooling cost and potential handling damage. Also, wave soldering is an extremely difficult way to achieve adequate hole fill on thermally challenging thick PCBs. By using PiP process with combination of solder preforms, it is possible to achieve adequate hole fill and reliable solder joints. This study investigated use and limitations of machine-placed solid solder preforms during top-side SMT reflow for PTH components. (IPC Apex/Expo, April 2011)