Foresite Inc.

Comparison of Testing Methods for Residues on Electronic Hardware

Dec 26, 2023 | Terry Munson

In this white paper, we discuss the pros and cons of five analytical techniques when applied to residue analysis on electronic assemblies. We evaluate the following for their application and limitations for analyzing both visible and invisible residues: FITR, SEM/EDX, XRF, Ion Chromatography, and ROSE...

Evaluation of No-Clean Flux Residues Remaining After Secondary Process Operations

Apr 17, 2023 | Phil Isaacs, Jennifer Bennett, Terry Munson

In an ideal world, manufacturing devices would work all of the time, however, every company receives customer returns for a variety of reasons. If these returned parts contributed to a fail, most companies will perform failure analysis (FA) on the returned parts to determine the root cause of the failure. Failure can occur for a multitude of reasons, for example: wear out, fatigue, design issues, manufacturing flaw or defect. This information is then used to improve the overall quality of the product and prevent reoccurrence. If no defect is found, it is possible that in fact the product has no defect. On the other hand, the defect could be elusive and the FA techniques insufficient to detect said deficiency. No-clean flux residues can cause intermittent or elusive, hard to find defects. In an attempt to understand the effects of no-clean flux residues from the secondary soldering and cleaning processes, a matrix of varying process and cleaning operation was investigated. Of special interest, traveling flux residues and entrapped residues were examined, as well as localized and batch cleaning processes. Various techniques were employed to test the remaining residues in order to assess their propensity to cause a latent failure. These techniques include Surface Insulation Resistance1 (SIR) testing at 40⁰C/90% RH, 5 VDC bias along with C32 testing and Ion Exchange Chromatography (IC). These techniques facilitate the assessment of the capillary effect the tight spacing these component structures have when flux residues are present. It is expected that dendritic shorting and measurable current leakage will occur, indicating a failing SIR test. However, since the residue resides under the discrete components, there will be no visual evidence of dendritic growth or metal migration....

Understanding Creep Corrosion Field Fails

Mar 16, 2022 | Phil Isaacs, Jing Zhang & Terry Munson

Dendrites, Electrochemical Migration (ECM) and parasitic leakage, are usually caused by process related contamination. For example, excess flux, poor handling, extraneous solder, fibers, to name a few. One does not normally relate these fails with environmental causes. However, creep corrosion is a mechanism by which electronic products fail in application, primarily related to sulfur pollution present in the air.1 The sulfur reacts with exposed silver, and to a lesser extent, exposed copper. This paper will explore various aspects of the creep corrosion chemical reaction...

Alternative Methods For Cross-Sectioning Of SMT And PCB Related Architectures

Sep 21, 2021 | Manuel J. Solis "Paco"

The electronics industry has been using the epoxy puck for the processing of the vast majority of electronics microsections since the 1970s. Minimal advancements have been seen in the methods used for precision micro-sections of PCBs, PCBAs, and device packages. This paper will discuss different techniques and approaches in performing precision and analytical micro-sections, which fuse the techniques and materials common in preparation of silicon wafers and bulk materials. These techniques have not only been found to produce excellent optical results, but transfer effectively to SEM for high magnification inspection and further analysis with minimal post-lapping preparation needed. Additionally, processing time is reduced primarily due to a significant reduction of bulk material removal earlier in the preparation, therefore needing less removal at later lapping steps compared to traditional sectioning methods. Additional techniques are introduced that mitigate some classic challenges experienced by technicians over the decades....

Failure Analysis – Using Ion Chromatography And Ion Chromatography/Mass Spec (IC/MS)

Apr 29, 2021 | Terry Munson

Since the 1980s the electronics industry has utilized ion chromatography (IC) analysis to understand the relationship of ions, and some organics, to product reliability. From component and board fabrication to complete electronic assemblies and their end-use environment, IC analysis has been the de facto method for evaluating ionic cleanliness of electronic hardware....

How Clean is Clean Enough – At What Level Does Each of The Individual Contaminates Cause Leakage and Corrosion Failures in SIR?

Sep 08, 2016 | Terry Munson, Paco Solis, Nick Munson, Steve Ring, Evan Briscoe.

In this investigation a test matrix was completed utilizing 900 electrodes (small circuit board with parallel copper traces on FR-4 with LPI soldermask at 6, 10 and 50 mil spacing): 12 ionic contaminants were applied in five concentrations to three different spaced electrodes with five replicas each (three different bare copper trace spacing / five replications of each with five levels of ionic concentration). The investigation was to assess the electrical response under controlled heat and humidity conditions of the known applied contamination to electrodes, using the IPC SIR (surface insulation resistance) J-STD 001 limits and determine at what level of contamination and spacing the ionic / organic residue has a failing effect on SIR....

Tin Whiskering on PCBA Capacitors in Storage (Inside ESD Bag, Inside a Sealed Cardboard Box)

Jan 13, 2011 | Terry Munson

The tin whisker failures investigated in this paper were found on functional RoHS-compliant hardware. The samples were not conformal coated. This paper will document the conditions associated with the whisker formation under the following conditions; tin ...