Technical Library | 2023-06-12 19:18:24.0
As any new technology emerges, increasing levels of refinement are required to facilitate the mainstream implementation and continual improvement processes. In the case of lead-free processing, the initial hurdles of alloy and chemistry selection are cleared on the first level, providing a base process. The understanding gained from early work on the base process leads to the next level of refinement in optimizing the primary factors that influence yield. These factors may include thermal profiles, PWB surface finishes, component metallization, solder mask selection or stencil design.
Technical Library | 2007-03-28 10:18:33.0
Legislation against the use of lead in electronics has been the driving force behind the use of lead-free solders, surface finishes, and component lead finishes. The major concern in using lead-free solders in the assembly and rework Chip Scale Packages (CSPs) is the relatively high temperatures that the components and the boards experience. Fine-pitch CSPs have very low standoff heights following assembly making inspection and rework of these components more difficult. One other concern pertinent to rework is the temperature of the neighboring components during rework. These issues, coupled with the limitations of rework equipment to handle lead-free reflow temperatures, make the task of reworking lead-free assemblies more challenging.
Technical Library | 2018-03-05 11:17:31.0
In order to comply with RoHS and WEEE directives, many circuit assemblers are transitioning some or all of their soldering processes from tin-lead to lead-free within the upcoming year. There are no drop-in replacement alloys for tin-lead solder, which is driving a fundamental technology change. This change is forcing manufacturers to take a closer look at everything associated with the assembly process: board and component materials, logistics and materials management, solder alloys and processing chemistries, and even soldering methods. Do not expect a dramatic change in soldering behavior when moving to lead-free solders. The melting points of the alloys are higher, but at molten temperatures the different alloys show similar behaviors in a number of respects. Expect subtler changes, especially near the edges of a process window that is assumed based on tin-lead experience rather than defined through lead-free experimentation. These small changes, many of them yet to be identified and understood, will manifest themselves with lower assembly yields. The key to keeping yields up during the transition to lead-free is quickly learning what and where the subtle distinctions are, and tuning the process to accommodate them.
Technical Library | 2013-06-05 23:14:44.0
The combination of higher lead-free process temperatures, smaller print deposits, and temperature restraints on electrical components has created difficult challenges in optimizing the reflow process. Not only are the electronic components and the PWB at risk, but the ability to achieve a robust solder joint becomes difficult, especially if the PCB is thermally massive. In addition, the constant miniaturization of electronic components, hence smaller solder paste deposits, may require the use of smaller particle-sized powders (...) This paper is a summary of best practices in optimizing the reflow process to meet these challenges of higher reflow temperatures, smaller print deposits, decreased powder particle size, and their affect on the reflow process.
Technical Library | 2021-08-25 16:34:37.0
As the traditional eutectic SnPb solder alloy has been outlawed, the electronic industry has almost completely transitioned to the lead-free solder alloys. The conventional SAC305 solder alloy used in lead-free electronic assembly has a high melting and processing temperature with a typical peak reflow temperature of 245ºC which is almost 30ºC higher than traditional eutectic SnPb reflow profile. Some of the drawbacks of this high melting and processing temperatures are yield loss due to component warpage which has an impact on solder joint formation like bridging, open defects, head on pillow.
Technical Library | 2007-10-18 13:42:45.0
To successfully achieve lead-free electronics assembly, each participant in the manufacturing process, from purchasing to engineering to maintenance to Quality/Inspection, must have a solid understanding of the changes required of them. This pertains to considerations regarding design, components, PWBs, solder alloys, fluxe s, printing, reflow, wave soldering, rework, cleaning, equipment wear & tear and inspection.
Technical Library | 2007-05-31 19:05:55.0
This paper discusses solder paste printing and flux dipping assembly processes for 0.4 and 0.5mm pitch lead-free WLCSPs and the corresponding assembly results and thermal cyclic reliability obtained. Variables evaluated include reflow ambient, paste type, and stencil design. Reliability is also compared to results for the same components assembled under identical conditions using SnPb solder.
Technical Library | 2024-06-23 22:03:59.0
The melting temperatures of most lead-free solder alloys are somewhat higher than that of eutectic Sn/Pb solder, and many of the alloys tend to wet typical contact pads less readily. This tends to narrow down the fluxing and mass reflow process windows for assembly onto typical organic substrates and may enhance requirements on placement accuracy. Flip chip assembly here poses some unique challenges. The small dimensions provide for particular sensitivities to wetting and solder joint collapse, and underfilling does not reduce the demands on the intermetallic bond strength. Rather, the need to underfill lead to additional concerns in terms of underfill process control and reliability. Relatively little can here be learned from work on regular SMT components, BGAs or CSPs.
Technical Library | 2008-11-20 00:46:10.0
The Sn/Ag/Cu family of alloys is the leading candidate for a lead-free alternative. The first part of this study was to determine if there is any significant difference between Sn/Ag/Cu alloys when used in automatic soldering equipment in terms of copper build-up in the system. The study compared two Sn/Ag/Cu alloys to determine if at processing temperatures one alloy would absorb less copper than the other alloy.
Technical Library | 2020-11-24 23:12:27.0
In a lead-free reflow process, temperatures are higher, and materials use outgasses more than in a leaded reflow process. The trends toward higher density populated boards and more pin-in-paste technology also increase solder paste use. More components and more solder paste result in more outgassing of chemistry during the reflow process. Some assemblies report condensation of vapors when the cold printed circuit board enters the oven. Little is known about the interaction between these condensed materials in terms of the interaction between these condensed materials and the reliability of the assembly. Apart from the question of reliability, a printed circuit board contaminated with a small film of residues after reflow soldering is not desirable.
