This paper discusses the reliability risks of using red phosphorus as a flame retardant material in encapsulated microcircuits. The focus is on chemical reactions, which can arise when red phosphorus is exposed to ambient humidity at high temperatures to form oxygen-containing phosphorus acids. These acids are corrosive and can alter the physical and electrical characteristics of the polymer composition and are root-cause candidates behind reported field failures in semiconductors encapsulated with epoxy resins containing red phosphorus flame- retardants.
Active Matrix Liquid Crystal Displays (AMLCDs) are used throughout the world in various industries while being subjected to a range of loading conditions. Extreme changes in temperature and humidity can wreck havoc on the sensitive layered structure. A slight bend or short distance impact can shatter the paper thin layer of glass, permanently damaging the structure. Due to the constantly changing LCD industry, always moving towards a smaller, faster, and clearer screen, methods need to be developed to quickly assess the life of an LCD. This study focused on characterizing the mechanical strength of an LCD assembly in comparison to a single layer of glass used in the same LCD assembly.
Thermal fatigue has been one of the most serious problems for solder joint reliability. Thermo-mechanical fatigue failure is considered to be closely related to micro-structural coarsening (grain/phase growth). Factors that influence the phase growth are studied and measurement methods are discussed, including the preparation of the eutectic solder sample for phase size measurement. Three categories of models used to predict grain growth in polycrystalline materials are presented. Finally, phase growth in solder during high temperature aging and temperature cycling and its use as a damage correlation factor are discussed.
Conformal coating is applied to circuit cards to provide a dielectric layer on an electronic board. This layer functions as a membrane between the board and the environment. With this coating in place, the circuit card can withstand more moisture by increasing the surface resistance or surface insulation resistance (SIR). With a higher SIR board, the risk of problems such as cross talk, electrical leakage, intermittent signal losses, and shorting is reduced.
This reduction in moisture will also help to reduce metallic growth called dendrites and corrosion or oxidation. Conformal coating will also serve to shield a circuit card from dust, dirt and pollutants that can carry moisture and may be acidic or alkaline.
The strength of glass panels is critical for the performance of touch-screen displays, especially in regards to how it responds to impact or drop. Insufficient drop testing performance can be related to two parameters: fracture strength and flaw size. The fracture strength of touch screen panels, everything else being equal, is primarily driven by the degree of strengthening performed on the surface of the glass. Glass of less than 1/8th inch thickness for touch screen panel applications tends to require a chemical strengthening process as thermal quenching can induce warpage in these thinner glass sheets. Chemical strengthening is performed through an ion-exchange mechanism, typically in a potassium-based solution. The larger potassium ion (r+ = 0.133 nm) substitutes for the smaller sodium ion (r+ = 0.098 nm), inducing a volumetric increase and creating residual compressive stresses at the outer layer of the glass (see Figure 1).
Flame retardants have been around since the Egyptians and Romans used alum to reduce the flammability of wood. Brominated flame retardants (BFRs) first experienced use after World War II as the substitution of wood and metal for plastics and foams resulted in materials that were much more flammable. The widespread use of BFRs initiated in the 1970s with the explosion of electronics and electrical equipment and housings. For the US market, all of these products must conform to the UL 94 flammability testing specifications. In fact, the most common printed circuit board (PCB) in the electronics industry, FR-4, is defined by its structure (glass fiber in an epoxy matrix) and its compliance to UL 94 V0 standard.
A very smart person once noted that all the problems in the world seem to occur at the boundary between one entity and another. While this analogy might be slightly overkill, it does place a spotlight on one of the most common problems in electronic and electro-mechanical design: board- to-board connections.
Board-to-board connections can be complex problems to solve, as they need to be responsive to a number of product requirements. Most critical of these are typically, cost, dimensional limitations, and the ability to perform rework. These problems can be solved, but designers are often not aware of the variations of board-to-board connections that are available and, due to competing requirements, can sometimes select solutions that satisfy some, but not all of the needs of the manufacturing process and the customer.
In this white paper, DfR will provide a brief overview of some of the more common board-to- board connections available and the process for selecting the optimum solution for your product design.
Wire bonding a die to a package has traditionally been performed using either aluminum or gold wire. Gold wire provides the ability to use a ball and stitch process. This technique provides more control over loop height and bond placement. The drawback has been the increasing cost of the gold wire. Lower cost Al wire has been used for wedge- wedge bonds but these are not as versatile for complex package assembly. The use of copper wire for ball-stitch bonding has been proposed and recently implemented in high volume to solve the cost issues with gold. As one would expect, bonding with copper is not as forgiving as with gold mainly due to oxide growth and hardness differences. This paper will examine the common failure mechanisms that one might experience when implementing this new technology.