A case study characterizes solder joint integrity of different BTC constructions in an accelerated lifetime test.
The electronics industry has extensively documented the influence of component construction on solder joint integrity. Materials used in the construction of a component package body result in a composite coefficient of thermal expansion (CTE) for the package that may result in the degradation of the package solder joint integrity. The industry discovered in the 2000s the construction design of ball grid array (BGA) packages had a significant influence on solder joint integrity. BGA solder balls located directly beneath and sometimes adjacent to the package internal die-to-package transition region (i.e., the die shadow region) failed first due to the CTE mismatch forces.1-3 Extensive finite element modeling, combined with use environment experiences and test data4-5 resulted in package redesign protocols that for the most part eliminated die shadow solder ball failure in BGA packages.
This paper documents an investigation of the impact of bottom-terminated component (BTC) package construction on solder joint integrity using thermal cycle testing (-55° to +125°C) in accordance with IPC-9701.
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Can a change of solvent in the printer improve SMT printing?
Any engineer will testify lab testing may not correlate with field results. Laboratory data are developed under ideal conditions to generate accurate and repeatable data, whereas a production setting introduces variables not reproducible in the lab environment.
In this report, AIM’s application lab approximated a production environment in a multi-hour printing test to quantify the effect of under-stencil wipe solvent on solder paste performance. This experiment compared isopropyl alcohol (IPA) and a novel stencil cleaner. IPA is not recommended as an in-process stencil cleaner, but is often used because it is inexpensive, effective and readily available. However, IPA is not a constituent of solder pastes and can therefore cause changes to paste that will negatively impact performance.
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Because electrochemical failure risk is site-specific, different components need different plans.
Highly dense electronic assemblies incorporate bottom-terminated components. Miniaturized components create numerous challenges, resulting in a shorter distance between conductors of opposite polarity, solder sphere size reduction, low-standoff gaps, flux entrapment under the bottom termination, blocked outgassing channels, and more significant potential for leakage currents.1
In the presence of humidity, moisture (mono-layers of water) hydrogen bonds with ionic contaminants to create an electrolytic solution. Ions such as flux activators can dissolve metal oxides present in the flux residue at the soldered connection.2 When the system is in operation, the electrical field attraction of the positively charged metal ions migrate to the negative conductor. These metal ions can plate small dendrites, resulting in leakage currents and/or parasitic leakage. As such, ionic residue testing is used to test for problematic residues that could hinder reliable circuit function.3
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The EMS behemoth is on the cusp of an all-automated future.
By almost any measure Universal Scientific Industrial is an EMS behemoth. Yet most of the press surrounding USI over the past few years has been tied to its recent acquisition of AsteelFlash. The deal, completed last month, added 17 manufacturing sites and about $1 billion in topline revenue. For the first time, USI will have sites in the US, Africa and Western Europe.
Today, USI has 27 manufacturing locations in 10 countries, over 24,000 employees and revenue of more than $7 billion. That’s good for the 11th spot in the current CIRCUITS ASSEMBLY Top 50 rankings. There’s no missing the company now.
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As a pandemic crashed the industry, EMS companies responded with vigor and speed.
2020 will be remembered as the year of Covid-19. It hit China first, spurring a national response that included the shutdown of all industrial activities, including manufacturing.
That’s no small matter. China produces some 90% of all electronics worldwide. In anticipation of the Chinese New Year, most companies outside China had increased their inventories of raw materials, so the impact on the supply chain wasn’t immediately felt. As buffer stocks dwindled, producers in the US and Europe were socked with virus-related shutdowns. Meanwhile, China came back online. So, while materials weren’t always where manufacturers needed them, even critical components generally were accessible in relatively short order.
Throughout much of the West, demand for most end-products ground to a halt. Aerospace, especially for commercial jets, and industrial electronics were hit hardest, offset for some by spikes in demand for PCs, tablets and related networking gear as telecommuting for work and school became an overnight worldwide phenomenon.
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Results of melting behavior, solder joint formation, tensile strength and high-temperature creep tests.
There has always been a latent interest in low-temperature solders, as they can 1) potentially reduce material cost by enabling use of cheaper PCBs and components due to the lower processing temperature, 2) promote long-term reliability by reducing exposure to thermal excursion, 3) reduce labor cost, 4) reduce energy cost, and 5) reduce dynamic warpage in sensitive components.
SnPb alloys have been historically used for making joints. In the case of electronics, eutectic 63/37 SnPb was a very good choice, as solder joints could be soldered at relatively low temperatures, considering its melting point at 183°C. Eutectic SnPb also produced solder joints with very good mechanical reliability. The transition to lead-free was mostly a matter of regulatory compliance, and in the early 2000s various lead-free alloys were considered substitutes for eutectic SnPb, including the eutectic 42Sn58Bi alloy.
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Press Releases
- ZESTRON Hosts Webinar on “Electronic Assembly Failures, Solutions and Lessons Learned for Long Term Reliability”
- Surface-Mount Innovations Delivering More for Less
- Freemelt to Outsource Production to Scanfil
- TAGARNO and Comtree to Host Live Webinar on Digital Microscopes in Canadian Electronics Manufacturing; Jake Kurth Comments