Book Excerpt: The Printed Circuit Assembler’s Guide to... Low-Temperature Soldering, Vol. 2, Chapter 5

Estimated reading time: 1 minute

By Morgana Ribas, Pritha Choudhury, Ramakrishna H V, and Rahul Raut, MacDermid Alpha Electronics Solutions

Chapter 5: Unveiling a Total Solution for Soldering Through-hole Components Using a Low-temperature Alloy

Electronic assembly developers have a myriad of material and process choices to make, and low- temperature soldering is a process increasingly being considered for various assembly needs. LTS is attractive for a range of advantages:

• Potentially reduces material cost by enabling the use of lower cost PCBs and components due to lower processing temperature
• Promotes long-term reliability by reducing exposure to thermal excursion
• Long-term reliability is promoted by improvement in micro-via lifetime performance
• Lower energy cost
• Lower dynamic warpage in sensitive components
• Improved memory cell retention in high-density memory products such as LPDDR5

Use of the same low-temperature alloy for solder paste and solid solder provides a total solution for assembling a wider variety of electronic packages, including through-hole components.

The key benefits of using a low-temperature alloy for through-hole components are:

• Enables the use of low temperature in selective soldering
• Enables soldering processes with heat-sensitive substrates, components, or board materials
• Provides efficiencies in both energy and cost versus standard lead-free alloys
• Reduction of warpage up to 99% (component and board/substrate) vs. SAC305 processes
• Comparable mechanical performance with SAC305 under certain conditions
• Cost effective

Solder joints are an essential part of electronic devices that provide an electrical connection as well as a mechanical and thermal bond. Increased digitalization and greater connectivity are driving factors for miniaturization and more complex and integrated designs in electronics. With shrinking real estate on the PCBs, package sizes continue to shrink and the demand for reliability only increases. The requirement for solders with higher thermal and electrical reliability is the most important technology driver for designing new soldering materials. The ability of soldering at lower temperatures needs to be balanced with the thermal and mechanical reliability requirements for a specific application. The higher reflow temperature required for soldering a hybrid solder joint involving SAC BGA can potentially result in soldering defects such as non-wet opens, solder bridging, head on pillow, and non-contact opens in packages such as Package on Package (PoP) bottom and PoP memory. Low-temperature soldering is becoming a crucial technology, as it helps prevent defects caused by warpage in ultra-thin, high I/O CSP packages used in complex electronic devices.

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