Converting wave soldering equipment to Pb-free: a pair of approaches for incorporating a low-cost wave solder pot.

Ed.: For the full article, please see circuitsassembly.com/cms/content/view/1817/

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With the introduction of Pb-free solders on the production floor, there have been several questions on converting a SnPb wave soldering process to accommodate a Pb-free solder alloy. Some facilities resign themselves to acquiring a new wave soldering system for Pb-free solder alloys, but that can be costly. The Electronics Manufacturing Productivity Facility (EMPF) faced this dilemma. Instead of purchasing a new system, the facility converted the existing system to accommodate both SnPb and Pb-free solders. It was not as simple as acquiring and installing a new solder pot, the EMPF found.

High Sn content solders can have a devastating effect on traditional solder pots. Sn surface erosion dissolves the base metals typically used to manufacture solder pots (Figure 1). Pb-free solder alloys also dissolve metals often used in soldering fixtures, like aluminum, copper and brass. This surface erosion phenomenon will quickly contaminate the Pb-free solder and affect soldering quality.

Technical Devices, a partner of the EMPF, developed a solution for Sn-induced erosion by coating solder pots with a titanium nitride finish. Titanium nitride serves as an effective barrier to Sn. The titanium nitride coating is molecularly bonded to the stainless steel, providing the solder pot and its critical components a protective barrier against the solvent action of Sn. Some of the most critical components in the solder pot and pump assembly are made of pure titanium and then coated with titanium nitride, preventing Sn-induced surface erosion.

There are two ways to remove a solder pot from a wave system and install a new pot. The first procedure assumes that the wave system lacks the convenient quick-disconnect electrical and mechanical connections for the SnPb pot and the Pb-free pot. This procedure may be employed when installing a new Pb-free pot, depending upon the capabilities and flexibility of the wave manufacturer. The approximate time to perform this procedure is eight hours.

[FIGURE 1 OMITTED]

This article details two procedures for converting to a Pb-free solder pot.

The American Competitiveness Institute is a scientific research corporation dedicated to the advancement of electronics manufacturing processes and materials for The Department of Defense and industry. Beginning with this issue, ACI will author a regular series on manufacturing.

Lee Whiteman is senior manufacturing engineer and Jeff Stong is EAD coordinator at American Competitiveness Institute (aciusa.org); [e-mail]. Debbie Alavezos is technical sales manager at Technical Devices Co.