-
- News
- Books
Featured Books
- smt007 Magazine
Latest Issues
Current IssueComing to Terms With AI
In this issue, we examine the profound effect artificial intelligence and machine learning are having on manufacturing and business processes. We follow technology, innovation, and money as automation becomes the new key indicator of growth in our industry.
Box Build
One trend is to add box build and final assembly to your product offering. In this issue, we explore the opportunities and risks of adding system assembly to your service portfolio.
IPC APEX EXPO 2024 Pre-show
This month’s issue devotes its pages to a comprehensive preview of the IPC APEX EXPO 2024 event. Whether your role is technical or business, if you're new-to-the-industry or seasoned veteran, you'll find value throughout this program.
- Articles
- Columns
Search Console
- Links
- Events
||| MENU - smt007 Magazine
Low-temperature Solder Paste Process Advantages
October 31, 2018 | Traian C. Cucu, Alpha Assembly Solutions, and Ioan Plotog and Mihai Branzei, Politechnica University of BucharestEstimated reading time: 7 minutes
Environmental issues are becoming increasingly important to organizations and individuals alike. The electronic assembly industry, like everyone else, is becoming more conscious about environmentally friendly processes and materials. This movement brings low-temperature processes and materials back into the spotlight because they can help with energy consumption and a reduced carbon footprint for assembly processes.
Tin/bismuth alloys have been used for a while in lead-free assembly processes in electronic assembly, one of the main concerns being the compatibility with the SAC (SnAgCu) spheres from ball grid array (BGA) and chip-scale package (CSP) components. Due to lower process temperatures, new chemistry platforms for solder paste need to be developed to fulfill both the assembly process requirements and the final assembly reliability. Solder joints are the result of the soldering process consisting of the temperature gradient action over the solder paste volume at the interface between pins and pads [1, 2]. Overall, the solder joint performance is described by the intermetallic formation at the interface of pad and solders volume as well as the pin and solder volume [3, 4]. The reduction of carbon footprint and the potential dollar savings add to the appeal of the low-temperature process [5].
The advantages of a low-temperature assembly process have long been a target for the assembly industry. Many attempts have been made by material suppliers to come up with an appealing chemistry platform that will allow the use of a low-temperature solder paste on an existing SMT line without major equipment changes (if any at all). Of importance, from the assembly process point of view, were the printability of the new platform and voiding performance. The printing performance of the proposed chemistry platform was evaluated using transfer efficiency (TE) for two aperture shapes—circle and square—as process indicators [6].
Practical
For the printing experiment, we used a DEK horizon printer with a four-mil stainless still stencil. We used a Keyence microscope for the visual inspection after printing and a Koh Young 8030 for the paste volume measurement after printing.
Four different printing experiments have been carried out to gather data for the following printing process indicators:
- Finest feature to print
- Print volume repeatability
- Response to pause
- Stencil life
This process indicators will provide a valuable indication of the rheological performances of the solder paste. After the reflow, we evaluated:
- Voiding
- Drop shock
- Thermal cycling
Transfer Efficiency
The stencil design used both square and round apertures 100–250 µ starting with an aspect ratio (AR) of 0.25 to force a failure and find the breaking point for the printing process. The finest feature to print was evaluated using the transfer efficiency process indicator. The combined transfer efficiency for the printing process for square and circle apertures is shown in Figure 1.
Figure 1: Combined transfer efficiency results for square and circle shaped apertures.
As pass/fail criteria, we used 50% transfer efficiency for the minimal acceptable value with the condition to have all values above that value, including any outliers that may occur.
Print Volume Repeatability
Print volume repeatability is the next process indicator used to characterize the paste performance. The print volume repeatability examines the printed solder paste volume repeatability for a given aperture at different printing speeds.
In Figures 2–4, we have the results for AR= of 0.6, 0.75, and 1, respectively. We used four printing speeds for this test with the printing parameters adjusted for optimum output for each speed.
Figure 2: Print volume repeatability for AR=0.60.
Figure 3: Print volume repeatability for AR=0.75.
Figure 4: Print volume repeatability for AR=1.
Response to Pause
The response to pause test evaluates the printed solder paste volumes variability for the first four consecutive prints, which provides valuable information about the capacity of a paste to recover after pause (i.e., the print strokes needed for the paste to recover after pause).
The response to pause test was carried out using the following process conditions:
- Out of jar
- After kneading
- One-hour pause without wipe
- One-hour pause with wipe
- Two-hour pause with wipe
Page 1 of 3
Suggested Items
Connect the Dots: Designing for Reality—The Pre-Manufacturing Process
05/08/2024 | Matt Stevenson -- Column: Connect the DotsI have been working with Nolan Johnson on a podcast series about designing PCBs for the reality of manufacturing. By sharing lessons learned over a long career in the PCB industry, we hope to shorten learning curves and help designers produce better boards with less hassle and rework. Episode 2 deals with the electronic pre-manufacturing process. Moving from CAD (computer-aided design) to CAM (computer-aided manufacturing) is a key step in PCB manufacturing. CAM turns digital designs into instructions that machines can use to actually build the PCB.
AIM Solder Signs Shinil Fl Ltd. as New Distributor for Korea
05/08/2024 | AIM SolderAIM Solder, a leading global manufacturer of solder assembly materials for the electronics industry, is pleased to announce a new distribution partnership with Shinil Fl Ltd., a prominent supplier of technological solutions in the SMT and semiconductor sectors.
Indium Corporation to Showcase HIA Materials at ECTC
05/07/2024 | Indium CorporationAs an industry leader in innovative materials solutions for semiconductor packaging and assembly, Indium Corporation® will feature its advanced products designed to meet the evolving challenges of heterogeneous integration and assembly (HIA) and fine-pitch system-in-package (SiP) applications at the 74th Electronic Components and Technology Conference (ECTC), May 28‒31, in Denver, Colorado.
Indium Corporation Expert to Present on Pb-Free Solder for Die-Attach in Discrete Power Applications
04/30/2024 | Indium CorporationIndium Corporation Product Manager – Semiconductor Dean Payne will present at the Advanced Packaging for Power Electronics conference, hosted by IMAPS, held May 8-9 in Woburn, Massachusetts, USA.
Taiyo Circuit Automation Installs New DP3500 into Fuba Printed Circuits, Tunisia
04/25/2024 | Taiyo Circuit AutomationTaiyo Circuit Automation is proud to be partnered with Fuba Printed Circuits, Tunisia part of the OneTech Group of companies, a leading printed circuit board manufacturer based out of Bizerte, Tunisia, on their first installation of Taiyo Circuit Automation DP3500 coater.