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Reliability Assessment of No-clean and Water-soluble Solder Pastes, Part IIMay 6, 2015 | Emmanuelle Guéné and Steven Teh, Inventec Performance Chemicals
Estimated reading time: 2 minutes
Note: Part 1 of this article published in the March 2014 issue of SMT Magazine, available here.
Twenty-five years ago, solder paste residues had to be cleaned after reflow due to their corrosive nature: two ways of cleaning were available, either with solvent or by using water, with or without detergent. Now, the assembly world is mainly no-clean: paste formulation is safer in terms of chemical reliability and process costs are reduced without cleaning. However, some applications (i.e., military, aerospace, high-frequency, and semiconductor) require a perfect elimination of the residue after reflow. Several options can achieve this result: a no-clean paste which allows residue to be removed with the most suitable cleaning method, or a paste designed to be cleaned, such as a water-soluble solder paste.
Water-soluble solder pastes generally show great wettability because of their strong activation but they are also known to have shorter stencil life and to be more sensitive to working conditions as temperature and humidity, compared to the no-clean pastes. Additionally, with the components stand-off getting smaller and smaller, washing residues with water only is more and more challenging due to its high surface tension: the addition of detergent becomes often necessary.
The purpose of this article is to highlight the differences between these two families of solder pastes to guide users in their choice. This will be achieved through the comparison of several recent water-soluble and no-clean formulations as far as reliability is concerned. First, the printing quality will be evaluated (viscosity, tack, cold slump, printing speed according to pressure, stencil life, idle time, printing consistency). Next, the reflow properties will be compared (hot slump, solderballing, reflow process window, wetting ability on different finishes).
Finally, the residue cleanability will be assessed. The IPC SIR will be also done to conclude the study. Both standardized tests and production tests will be used to evaluate the performance of these two kinds of solder pastes.
Six lead-free pastes were extensively studied, three being water-soluble and three being no-clean. The first part of the study focused on printing performance. The pastes were characterized using standardized tests and internally developed tests: dynamic viscosity, tackiness, slump and solderballing. The influence of accelerated storage at elevated temperature, the influence of time and conditions between printing and reflow and the influence of continuous shear according to time were shown. The printing performances were also evaluated in a printer. Although the number of pastes studied was restricted, the water- soluble pastes generally yielded results below the no-clean pastes with more sensitivity to temperature and humidity, tendency to slump during preheat and narrower printing window. Water- soluble solder pastes must be stored, handled and used with more caution before reflow.
In the second part of the paper, the reflow properties will be compared: wettability, reflow process window, anti-graping properties. Finally the residue cleanability with water, then with water and detergents will be examined. The cleanliness will be assessed using visual inspection, ionic contamination and surface insulation resistance tests.
Editor's Note: This article originally appeared in the April issue of SMT Magazine.
Indium Corporation to Showcase Proven EV Products and High-Reliability Alloys at Productronica China02/28/2024 | Indium Corporation
As a materials pioneer and trusted partner in electric vehicle (EV) and e-Mobility manufacturing, Indium Corporation is proud to showcase its high-reliability alloys and soldering solutions at Productronica China, March 20-22, in Shanghai.
Absolute EMS, Inc., an award-winning EMS provider of turnkey contract manufacturing services, continues to harness the power of nitrogen to enhance the quality, reliability and efficiency of their manufacturing processes. The company’s state-of-the-art facilities are equipped with nitrogen reflow ovens and selective soldering machines, ensuring consistent, high-quality results for every project.
KYZEN, the global leader in innovative environmentally friendly cleaning chemistries, will exhibit at the SMTA Monterrey Expo & Tech Forum, scheduled to take place Thursday, March 14, 2024 at the Cintermex Convention Center, Hall 2A in Monterrey, Nuevo León. KYZEN will showcase the new aqueous chemistry AQUANOX A4618 in addition to highlighting stencil cleaning chemistries KYZEN E5631J and CYBERSOLV C8882.
The challenges of the Corona crisis have further accelerated this trend. Many companies now offer only online events, whether due to time or cost reasons. However, at Rehm Thermal Systems, you have a choice: the provider of thermal systems for various industries offers a variety of short, concise online webinars and complements them with in-depth in-person seminars on various topics.
Hentec Industries/RPS Automation, a leading manufacturer of selective soldering, lead tinning and solderability test equipment, is pleased to announce that Dynamic Grid has ordered a Hentec Industries/RPS Valence 3508 selective soldering system.