Standardization is helpful but not always the best solution.

In the electronics manufacturing services environment, product design is “controlled” by 30 or more customers, plus the EMS company, which limits the degree to which Lean manufacturing initiatives can be implemented. In the EMS realm, there is often a need to tailor continuous improvement efforts based on individual customers’ products and objectives. Lean in this environment is more of a toolbox, where different groups of tools are used to support each customer. We’ve discussed many of these tools in our columns over the years. This month we look at how they can best be combined to deliver superior quality and service in a multi-customer environment.

Some disciplines are transparent to the customer and best applied holistically as the foundation for a Lean organization. These include:

• 5S or 5 Pillars philosophy (sorting, set in order, sweeping or shining, standardize and sustain). Setting up a clean factory and keeping it orderly are core concepts that drive efficiency and high quality by making inefficiency very visually obvious.

• Clear design guidelines. While not all customer designs will conform to best practices, every customer should be provided with design guidelines so they are aware of best practices. Guidelines that track closely to industry standards are more likely to be adopted than those that reflect a unique internal recipe.

• Lean practices in supply-chain management. At a holistic level, there should be a clear vision of optimum raw material lot sizes, a standardized forecasting methodology and a supply-chain management strategy that encourages suppliers to support Lean initiatives.
Personnel cross-training. Training personnel in multiple operations so that they can be shifted to various operations as needed helps optimize capacity by providing a fast way to eliminate bottlenecks.

• Continuous improvement training. Training in problem-solving disciplines such as Six Sigma can be done holistically; however, the application of these techniques may be very focused.

• Point of use stocking. Obtaining extra feeders and doing line side stocking to minimize changeover time can be beneficial across the board.

Other disciplines are best used in more focused approaches:

• Standardized equipment platforms. While standardizing on core equipment platforms throughout an organization can create highly efficient factories and reduce capital expenditure requirements, it can be impractical when a diverse mix of customers is present. Focusing on minimizing variation as a holistic goal, while configuring lines and work cells to best meet the needs of each facility’s customer base, can be more practical. Standardization of SMT equipment, rail widths and functional test platforms to the extent practical can increase schedule flexibility and minimize bottlenecks. Standardizing functional test platforms can minimize maintenance costs and reduce both fixturing costs and fixture lead-time.

• Application of Six Sigma techniques. While some companies make the search for kaizen events a mission in itself, in the EMS environment, Six Sigma techniques may be more powerful as a tool for addressing specific customer issues rapidly. For example, when one of our teams applied Six Sigma’s Define, Measure, Analyze, Improve, Control (DMAIC) approach to a quality issue in our facility in Juarez, Mexico, it was determined that the root cause was illumination values that were causing misaligned placement against the pads on certain BGAs and ICs. As a result, the team was able to rapidly correct the problem.

• DfM/DfT recommendations. Development of design guidelines should be done holistically. Specific DfM/DfT recommendations should be made on a customer-by-customer basis. EPIC Technologies uses a 5-point ranking scale to make it easier for customers to understand the level at which noncompliance will impact product quality.

• Lean supply chain management philosophy. The concept of setting material bonds for raw material with the supply base and holding finished goods kanbans for each customer is a good holistic practice, but the reality is that this will also need to be customized and often modified for each customer. Additionally, many customers will have some suppliers on their approved vendor list (AVL) not willing to comply with preferred Lean practices.

• Value Analysis Value Engineering (VAVE). This is perhaps the most powerful technique for applying Lean philosophy on a customer-by-customer basis, because it educates and motivates the customer’s team through a collaborative brain-storming improvement process with defined cost benefits over time.

Taking a customized approach to Lean manufacturing philosophy, and using some tools universally while tailoring others for customers willing to optimize their product design, supply base and product-ordering patterns, provides the best of both worlds. It provides immediate benefits to customers wishing to fully utilize the toolbox, while providing a scalable solution to those who may be willing to integrate Lean principles into their designs over time.

Todd Baggett is EPIC Technologies’ senior vice president, sales and account management; todd.baggett@epictech.com.

A selective soldering machine can be used to fix misaligned parts.

OK, I confess. Sometimes we do make mistakes. As much as I hate to admit it, it does happen. For example, we’ve seen headers not fully seated to the board. They’re a little crooked, or one edge is touching the PCB, while the other edge is so far up in the air that you can’t even see the pin protruding through the other side of the board. Other times, an edge connector needs to protrude through a cover panel and there’s no room for play. The connector must be perfectly flat and perfectly square. If you find yourself in this situation, your selective soldering machine can be your best friend.

Warning! On some machines, you may be required to bypass security features. Please consult your manufacturer before bypassing anything designed to protect you from a dangerous machine.

If the connector is larger than the size of the nozzle, program the machine to “walk” back and forth over the pins of the connector (Figure 1). There’s a limit to how long a connector could reasonably be reworked using this method. We’ve been able to fix 2"-long connectors on four-layer boards. The key was to make sure the nozzle could dwell a little bit on the pins that were connected to ground.

Figure 1. A selective soldering machine can be programmed to move back and forth over the pins of a  large connector.

Every connector is different. Some connectors will become damaged after much exposure to heat. The plastics are not designed to handle it. For these connectors, we find it’s best to remove the entire connector and insert a new one. Other connectors, however, hold up well under the heat, and you’ll be able to apply slight pressure with your hand to push them back through the board. Be careful, however, as in many cases, pushing the pins down will also push the solder down, and you’ll have no topside fillet.

Make sure to preheat the board. You don’t want to hit this cold board with a bunch of molten solder. The thermal shock could shorten the lifetime of the assembly. Make sure it’s nice and hot before you begin.

Chris Denney is chief technology officer at Worthington Assembly (worthingtonassembly.com); cdenney@worthingtonassembly.com.

Poorly maintained baths or improper wave settings can lead to whiskers.

A solder whisker or a dross short is surface contamination found after soldering due either to a poorly maintained solder bath or incorrect setting of a wave. If a solder bath is poorly maintained, dross can be present in the ducting below the solder surface. When the wave operates, any dross can emerge randomly in the wave and contact the board and form micro shorts.

In the case of the back flow on a lambda style wave, the solder should flow at the same speed as the board or slightly faster. The board displaces any surface oxides on the surface of the wave before it can contact the base of the board. If the wave stops flowing before the board exits the wave, the board will contact the surface oxide, leading to what is sometimes referred to as “snail trails.” This can also be seen on waves running nitrogen where only the surrounding areas of the wave are inserted.

Similar micro shorts have been seen during wave soldering in a Pb-free process where the copper level is excessive and the temperature has permitted SnCu needles to form and flow in the wave. The same is true if the surface of the tank becomes eroded, permitting SnCuFe needles in the bath. Both these contamination issues can lead to very fine needle-like solder shorts. The excess copper can be overcome by balancing the copper levels with tin. SnCuFe is a real problem not only to the system but also the extremely expensive alloy, which will need to be changed.

These are typical defects shown in the National Physical Laboratory’s interactive assembly and soldering defects database. The database (http://defectsdatabase.npl.co.uk), available to all this publication’s readers, allows engineers to search and view countless defects and solutions, or to submit defects online. To complement the defect of the month, NPL features the “Defect Video of the Month,” presented online by Bob Willis. This describes over 20 different failure modes, many with video examples of the defect occurring in real time.

Figure 1. Solder whisker bridging two conductors.

Chris Hunt is with the National Physical Laboratory Industry and Innovation division (npl.co.uk); chris.hunt@npl.co.uk. His column appears monthly.

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