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.
AIM Solder, a leading global manufacturer of solder assembly materials for the electronics industry, is pleased to announce its new NC259FPA Ultrafine No Clean Solder Paste, which it revealed recently during the Productronica Germany trade show.
Real Time with... productronica 2023: Koh Young Discusses Semiconductor and Advanced Packaging Inspection11/27/2023 | Real Time with...productronica
Koh Young’s Harald Eppinger talks about the company’s technology for the semiconductor and advanced packaging market and how they address the challenges introduced by reflective components and micro solder deposits.
HyRel Technologies Attains ITAR Registration, Reinforcing Leadership in Robotic Solder Component Tinning11/27/2023 | HyRel
HyRel Technologies, a global provider of quick turn semiconductor modification solutions, announces the achievement of International Traffic in Arms Regulations (ITAR) registration.
Mek (Marantz Electronics), a leader in Automated Optical Inspection (AOI) solutions, used last weeks’ Productronica show in Munich to proudly introduce the SpectorBOX X series, a modular full 3D AOI system for THT solder joints and THT components.
Productronica 2023 played host to the IPC World Hand Soldering Competition, bringing talented regional solder champions from all over the globe to compete for the title of World Champion. Each competitor was given sixty minutes to assemble a complex printed circuit board with their performance judged in accordance with IPC-A-610 Class 3 criteria. Each competitor’s efforts were rated on the merits of the results achieved, scored on the quality of the assembly process, the electrical functionality of the assembly and the speed at which the assembly was produced.