Technical Library | 2020-05-08 18:22:31.0
A customer contacted the Helpline to perform analysis on a lead-free assembly which exhibited intermittent functionality. The lead-free assembly exhibiting intermittent functionality when pressure was applied to the ball grid array (BGA) packages. Industrial adaptation of a Restriction of Hazardous Substances (RoHS) compliant solder standard has created a new host of failure modes observed in lead-free assemblies. Pad cratering occurs when fractures propagate along the epoxy resin layer on the underside of the BGA connecting pads. While originating from process, design, and end use conditions, it is the combination of a rigid lead-free solder with inflexible printed circuit board (PCB) laminates that has advanced the prevalence of this condition. Pad cratering is simply the result of mechanical stress exceeding material limitations.
Technical Library | 2021-03-10 23:57:29.0
Latent short circuit failures have been observed during testing of Printed Circuit Boards (PCB) for power distribution of spacecraft of the European Space Agency. Root cause analysis indicates that foreign fibers may have contaminated the PCB laminate. These fibers can provide a pathway for electromigration if they bridge the clearance between nets of different potential in the presence of humidity attracted by the hygroscopic laminate resin. PCB manufacturers report poor yield caused by contamination embedded in laminate. Inspections show ...
Technical Library | 2012-07-19 21:24:02.0
First published in the 2012 IPC APEX EXPO technical conference proceedings. With the ever accelerating demands in printed circuit board (PCB) design, the choices of advanced laminate materials have become fewer and fewer. The trends continue towards high
Technical Library | 2019-02-06 22:02:08.0
The High Density Packaging (HDP) user group has completed a project to evaluate the majority of viable Dk (Dielectric Constant)/Df (Dissipation Factor) and delay/loss electrical test methods, with a focus on the methods used for speeds above 2 GHz. A comparison of test methods from 1 to 2 GHz through to higher test frequencies was desired, testing a variety of laminate materials (standard volume production with UL approval, low loss, and "halogen-free" laminate materials). Variations in the test board material resin content/construction and copper foil surface roughness/type were minimized. Problems with Dk/Df and loss test methods and discrepancies in results are identified, as well as possible correlations or relationships among these higher speed test methods.
Technical Library | 2016-10-20 18:13:34.0
Pad cratering failure has emerged due to the transition from traditional SnPb to SnAgCu alloys in soldering of printed circuit assemblies. Pb-free-compatible laminate materials in the printed circuit board tend to fracture under ball grid array pads when subjected to high strain mechanical loads. In this study, two Pb-free-compatible laminates were tested, plus one dicycure non-Pb-free-compatible as control. One set of these samples were as-received and another was subjected to five reflows. It is assumed that mechanical properties of different materials have an influence on the susceptibility of laminates to fracture. However, the pad cratering phenomenon occurs at the layer of resin between the exterior copper and the first glass in the weave. Bulk mechanical properties have not been a good indicator of pad crater susceptibility. In this study, mechanical characterization of hardness and Young’s modulus was carried out in the critical area where pad cratering occurs using nano-indentation at the surface and in a cross-section. The measurements show higher modulus and hardness in the Pb-free compatible laminates than in the dicy-cured laminate. Few changes are seen after reflow – which is known to have an effect -- indicating that these properties do not provide a complete prediction. Measurements of the copper pad showed significant material property changes after reflow.
Technical Library | 2015-08-13 15:52:40.0
Pad cratering has become more prevalent with the switch to lead free solders and lead free compatible laminates. This mainly is due to the use of higher reflow temperature, stiffer Pb-free solder alloys, and the more brittle Pb-free compatible laminates. However, pad cratering is difficult to detect by monitoring electric resistance since pad cratering initiates before an electrical failure occurs. Several methods have been developed to evaluate laminate materials' resistance to pad cratering. Pad-solder level tests include ball shear, ball pull and pin pull. The detailed methods for ball shear, ball pull, and pin pull testing are documented in an industry standard IPC-9708. Bansal, et al. proposed to use acoustic emission (AE) sensors to detect pad cratering during four-point bend test. Currently there is an industry-working group working on test guidelines for acoustic emission measurement during mechanical testing.
Technical Library | 2020-11-29 22:02:49.0
It has been over 25 years since the earliest edition of "Everything You Ever Wanted to Know About Laminates...but Were Afraid to Ask" was pounded out on an old TRaSh-80 Computer. It has undergone periodic review and editing, including adaption for use on our website. (When I entered the industry Al Gore had not yet invented the internet.) Before I "retired" in 2004, we did another minor revision, but it was largely cosmetic, removing most references to the old military specification and introducing IPC-4101, the "new" specification for laminate and prepreg materials.
Technical Library | 2017-08-24 16:53:20.0
With the rapid development of the information industry, increasing attention is being paid to the dielectric performance of base materials including copper-clad laminates (CCL) and prepregs. In addition to the increasingly high performance requirements of CCL's, the present global attention to less toxic products is leading to an increase in the use of halogen-free flame retardants in electronics. (...) This paper introduces a new phosphonate oligomer which can be used as a reactive flame retardant in epoxy based resin systems. Suitable conditions for the complete reaction between the phosphonate oligomer and epoxy resin are described and the resulting halogen-free laminates with improved properties such as low Df, low coefficient of thermal expansion (CTE), high peel strength, and good toughness are presented.
Technical Library | 2013-05-16 15:52:00.0
In response to a growing concern within the Electronic Industry to the transition to Halogen-Free laminates (HFR-Free) within the Client Market space (Desktop and Notebook computers) iNEMI initiated a HFR-Free Leadership Workgroup to evaluate the readiness of the Industry to make this transition. The HFR-Free Leadership WG concluded that the electronic industry is ready for the transition and that the key electrical and thermo-mechanical properties of the new HFR-Free laminates can meet the required criteria. The HFR-Free Leadership WG verified that the laminate suppliers can meet the capacity demands for these new HFR-Free laminates and developed a "Test Suite Methodology" (TSM) that can facilitate the comparison and choice of the right laminate to replace brominated FR4 in the Client space... First published in the 2012 IPC APEX EXPO technical conference proceedings.
Technical Library | 2017-01-19 16:58:47.0
The biggest problem with designing rigid-flex hybrid PCBs is making sure everything will fold in the right way, while maintaining good flex-circuit stability and lifespan. The next big problem to solve is the conveyance of the design to a fabricator who will clearly understand the design intent and therefore produce exactly what the designer/engineer intended.Rigid-Flex circuit boards require additional cutting and lamination stages, and more exotic materials in manufacturing and therefore the cost of re-spins and failures are very much higher than traditional rigid boards. To reduce the risk and costs associated with rigid-flex design and prototyping, it is desirable to model the flexible parts of the circuit in 3D CAD to ensure correct form and fit. In addition it is necessary to provide absolutely clear documentation for manufacturing to the fabrication and assembly houses.
