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Process Control and Visual Management for Lead-free Hand and Wave Soldering
December 31, 1969 |Estimated reading time: 4 minutes
By Scott Mazur, Benchmark Electronics Inc.
Manufacturing facilities continue to produce both leaded and lead-free assemblies, given the various product and technology RoHS exemptions. Facilities that manufacture a variety of products using both alloys require controls and identification of the specific lead-free processes and equipment. These controls and identification are critical, given the historical use of leaded solders in every electronics manufacturing facility and the potential legal and financial consequences of shipping noncompliant material.Cross-contamination opportunities exist at both the hand and wave soldering operations. Within each process, multiple opportunities exist; such as incorrect leaded material received, equipment contamination, and the wrong leaded material used during manufacturing. The U.K. RoHS Enforcement authorities have noted several noncompliance findings detailing cross contamination of wave solder and hand solder processes. The specific information is referenced in the U.K. RoHS compliance and enforcement Website, rohs.gov.uk, in the enforcement's end of first year report, page 22. Deploying the following guidelines will decrease the risk opportunity and will support a manufacturers RoHS compliance assurance system.
Process ControlSpecific examples of cross contamination include the wrong solder wire material used during hand soldering and incorrect alloy (solder bar) being used to re-fill a wave solder or solder fountain bath. If either occurs, the result will be disastrous causing the product to be noncompliant. One detection tool that can be implemented as process control is X-ray fluorescence (XRF) verification. As noted in an SMT EMS Trends article "Due Diligence Verification,"1 XRF verification can be completed with a portable XRF analyzer to detect cross contamination and support a facility's due diligence program.
XRF can be conducted at various points of the process including material receipt and during manufacturing to verify RoHS compliance. One of the most critical areas includes the analysis of the solder pot, or bath, for the wave solder and solder fountain processes. Figure 1 details an example of a solder pot XRF analysis. The element being verified is lead and what levels in percentage by weight (% by Wt) exist. As shown in Figure 1, a run chart can be used to track the readings over time. Take action limits (TAL) should be implemented to investigate any data point that is at or over the limit. Given the RoHS banned substance maximum concentration limit for lead being 0.1 (% by Wt), a 0.08 TAL would escalate an investigation before a noncompliance occurs.
With various solder bar material, lead impurities exist. The lead impurity is naturally occurring and will vary depending on the purity of material purchased. Some solder bar material can measure up to 0.05 % by Wt of lead impurity. To complement the illustrated XRF measurements, additional laboratory testing can be conducted, such as arc emission spectroscopy, to validate the initial results. The XRF testing intervals should start off being frequent, with analysis of the data as the vehicle to expand the intervals. A weekly or daily test could expand to monthly if all testing measurements are within the take action control limit.1,2
Visual ManagementGiven the industry's transition to lead-free, identification of products that use leaded solder and the associated equipment and tooling becomes very important. Some examples of equipment and tooling for hand and wave soldering would be soldering irons; tips; wave solder fountains, pallets, carriers and scoops, or ladles. Visual management heightens the awareness for all employees who see and work on the product and reduces the risk for cross-contamination errors during an assembly operation. The identification used for the visual management can be tape, labels, or signs to segregate lead-free tooling.
Identification can be expanded to include chemistries (water-soluble and no-clean) and other materials that come in contact with solder during the process, such as a hand solder sponge, solder wick, and gloves. The specific risk is when the tool or material comes in contact with the leaded solder and this is transferred to a lead-free solder joint. The ultimate goal is to eliminate any cross-contamination risk of lead-free and leaded alloys that may exist within a facility that manufactures exempt and nonexempt assemblies, or incorporates lead-free due to supply chain pressures. Cross-contamination that results in the opposite condition, lead-free mixing into in a leaded process, would require the same controls as above with the focus on metallurgical formation and not regulatory compliance.
ConclusionThe deployment of the above process control and visual management practices will build a foundation that supports a manufacturer's compliance assurance system while reducing the cross-contamination risk of lead-free hand and wave solder manufacturing. By implementing visual management and XRF due diligence verification controls, a manufacturer can detect noncompliances internally, where problems can be corrected.
REFERENCES:1. "Due Diligence Verification Ensuring RoHS Compliance," SMT Magazine, March 2006.2. Shina, Sammy and Farrell, Bob, et al, "Green Electronics Design and Manufacturing Book," Chapter 6, McGraw Hill Publishing.
Scott Mazur, manufacturing staff engineer and RoHS specialist, Benchmark Electronics Inc., Hudson, N.H. division, may be contacted at (603) 879-7000 ext. 8004; scott.mazur@bench.com.