Designed properly, it’s actually okay if your machine makes contact with surface mount components.

One of the beautiful things about selective soldering machines (vs. wave soldering machines) is that they are easy to route around surface mount components mounted on the bottom side of the board. But it’s not always that easy. For example, what happens when the board designer ran out of room and placed surface mount components next to the through-hole components?

Believe it or not, contact can safely be made with surface mount components, so long as only one side of the component is reflowed at a time. This requires that the design of the board has the surface mount components perpendicular to the plated through-holes.

As shown in Figure 1, the path of the nozzle crosses directly over nine surface mount components. The area where the nozzle makes contact with the component will reflow the solder paste deposit, but the opposite side of the component will remain solid and hold the component in place. This can make one a little nervous the first time they try it, but rest assured, that component will stay put.

It would be a good idea to alert the board designers to this. Many designers like to use every square centimeter of the board, and knowing they can put surface mount components very close to plated through-holes, so long as they are perpendicular to the holes, will certainly make them happy.

Chris Denney is CTO at Worthington Assembly Inc; cdenney@worthingtonassembly.com.

An overview of today’s adhesive application technologies.

Automated dispensing of electronic materials in fluidic form is employed across the full range of electronics manufacturing, from board-level assembly to semiconductor applications. Materials dispensed can range from very low (water-like) to very high (toothpaste-like) viscosity and encompass many different functions. These include solder paste to electrically connect components, encapsulants to protect devices from atmospheric conditions, thermal interface materials (TIM) to help dissipate heat from parts, adhesives to attach parts to a substrate or assembly, and others.

Each material may be dispensed in a range of dot sizes or complex lines and patterns, depending on application requirements (Figure 1). Common applications include underfill, selective coating, fastening, dam and fill, potting and dielectric dispense. Shape and function are determined by the type of pump mounted in the dispenser. A dispenser may be fitted with more than one pump head type so that it can perform multiple dispense operations on a single substrate. For example, for an individual PCB or workpiece being processed, one pump head might be dispensing tiny adhesive dots 300µm in diameter to hold very small passive or chip components onto the assembly, while the other head is performing an encapsulation operation on a wire-bonded chip, or applying a selective coating.

Dispensing is a complex process with many different controllable variables. But essentially all dispensing is divided into two main sets of parameters: material and machine. Material parameters include such variables as viscosity, temperature stability, flow behavior, absence of air, wetting behavior and homogeneity. Machine parameters are all those software parameters a given system uses to be able to execute the process of dispensing the material.

With automated dispensing, there are different types of pump technologies used to precisely meter the deposition of materials, ranging from traditional auger-screw constructs to piston and streaming designs, and even cutting-edge technologies that involve noncontact and radical new fluid management technologies. Each type has its pluses, from reliability to speed to precision, whether the application is dot dispensing or streaming lines of material. Pump designs incorporate special materials or features to accommodate the types of material that they are dispensing; for example, some types of adhesives are filled with highly abrasive material that can quickly wear out pumps that aren’t built with carbide and sapphire components.

As requirements for smaller dot sizes and higher throughputs increase, OEMs must work even harder to offer dispense systems with higher accuracy and higher speeds. We see this in the new pump technologies offering faster cycle times and higher degrees of process control through more sophisticated software and more robust X, Y gantries for stability. To obtain higher accuracy and speed, DC linear motors and linear encoders are used to move the dispense heads around quickly and with precision. Proper gantry design enables higher speeds and accelerations up to 3g without sacrificing accuracy. With today’s automated dispense systems, speed, accuracy, and dispense control are paramount. Machine vision systems ensure accuracy, and more user-friendly GUI and software tools speed teaching and setup.

In terms of pump technologies, in addition to greater dispense control and smaller dot sizes, ease of setup and simple maintenance without overly involved cleaning procedures are goals, driven by the growing number of high-mix product environments where downtime between different product runs is money out of pocket.

Dispense equipment is trending toward smaller, more compact footprints to maximize limited factory floor space without compromising throughput. This often means dual-lane processing capability. Dual-lane processing permits parallel loading of production parts onto two lanes for continuous dispensing, eliminating lost time in non-dispensing activities such as material flow-out and substrate loading/unloading.

Michael Martel is product marketing engineer at Speedline Technologies; mmartel@speedlinetech.com.

The value engineering process not only improves manufacturability, it improves relationships.

As discussed in our January 2013 column, Value Analysis Value Engineering is a formal problem-solving process that can help improve productivity and value. While it has benefits as a tactical tool in a Lean manufacturing toolbox, it is even more powerful when used strategically.

VAVE has several benefits from a strategic standpoint. When implemented early in the product development lifecycle, it can become a scheduled part of the product lifecycle roadmap, driving down cost and mitigating obsolescence risk as the product enters each new phase of its lifecycle. A good VAVE strategy creates a series of cost-reduction ladders that unlock value at specific points in time, similar to the way bond ladders spread risk and optimize returns by sequencing redemption at set points in time. Most important, this ensures a proactive focus that minimizes the likelihood or impact of supply-chain interruption.

From a management perspective, it is also a good tool for driving a collaborative process between OEM engineering teams and a contractor’s engineering teams. One of the biggest fears engineering teams have about outsourcing is the potential loss of control or product knowledge as the contractor takes over responsibilities. VAVE opens the door to greater communications between the OEM’s product design and manufacturing engineering teams and the contractor’s engineering and manufacturing teams. This ensures that critical data about the product’s manufacturability and testability issues resident at the contractor are fed back to the engineering team at the OEM and can be used to not only improve the current product, but also enhance future product generations. Similarly, the contractor’s materials expertise may drive improvements in component selection in future products.

Finally, from a marketing standpoint, it provides OEM product managers with a greater range of options in terms of extending the life of mature products that still have viable markets, particularly when a full redesign may not be cost-effective. As an example, a manufacturer of a long-lifecycle product with a large installed user base was facing increased competition from companies offering a lower price. The current market was saturated, making a full redesign or new generation of products unfeasible. Yet, failing to address the cost competition would cause erosion in the existing business base.

A VAVE workshop at EPIC Technologies yielded over $225,000 in savings for one 20-year-old design. The list of proposed changes generated through the workshop included:

• Change drawing requirements to reduce cost.
• Re-layout PCB for cost and reduced scrap loss.
• Eliminate connectors and solder direct to PCB.
• Identity lower cost component alternatives.
• Identify and eliminate end-of-life components.
• Change to lower-cost cable terminations.
• Modify test sequence for earlier fault detection and repair.
• Reduce test time.
• Redesign circuit with lower cost design.
• Improve tester audible and visual clues.
• Re-source component supplier.
• Change packaging to be more efficient.
• Change SMT component lead type to be more robust in the field.
• Review supplier negotiation strategy.
• Move component location, reducing cabling cost.
• Change screw torque requirements, allowing use of lower cost screws.

Each option was costed so that the customer could evaluate cost savings against tradeoffs. Following a feasibility workshop, the customer provided feasibility assessment of the ideas presented, and an evaluation plan was jointly developed. The Idea Report tracking worksheet was used to track the recommendation, approved plan and cost savings.

The VAVE session drove a brainstorming effort that looked across multiple disciplines for possible cost-reduction opportunities. Instead of cutting profit margins to compete on price, the customer was able to cut manufacturing cost. Plus, existing product life was extended and market position preserved.

A robust VAVE process goes far beyond the benefits of optimizing component sourcing, manufacturability or testability. When implemented as it is done at EPIC Technologies, it drives a much closer relationship among program stakeholders and changes the contractor’s position from that of supplier to that of an equal member of the product team. The result is better product competitiveness, which can lead to increased market share with concomitant benefits for both OEM and contractor. Done strategically, this process ensures a proactive approach to unlocking value at specific points over the product’s lifecycle. It also reduces the potential for production interruptions related to obsolescence issues or unanticipated supply-chain interruptions.

Steve McEuen is director, commodity management at EPIC Technologies. He can be reached at steve.mceuen@epictech.com.

Don’t get caught with your bath down.

The topic of hot air solder leveling (HASL) has come up a handful of times recently and so the motivation for this column. An OEM currently using HASL but with advances in board designs had observed last month that the ball grid array patterns were not covering properly. They also experienced instances when component placement was off due to the uneven nature of the HASL deposit. They requested some information on “alternate finishes.”

The call came about 10 to 15 years later than I expected. A few days later, I visited a North American plating shop that finishes the majority of its products with various electrolytic and electroless nickel/gold plating. A “good percentage” of its product remains HASL, and they asked when HASL would go away. The process is not a favorite among the operators.

When I came to MacDermid 15 years ago, the industry was investigating alternate surface finishing. The term “alternate” referred to anything that was not HASL. The buzzword was planar; there was a need for a flat surface finish to accommodate new designs with miniature components. As a result of components getting smaller and, specifically, the use of BGAs, HASL was becoming difficult to use. The uneven surface could not ensure proper component alignment or connectivity. In addition, substrates were getting thinner, and the laminates could not withstand submersion into molten solder. For many, the need to switch from HASL was imminent.

My first business trip in the industry was to the coast of England to install an immersion silver process. I was fresh out of college and had been convinced that immersion silver was the next-best surface finish and that it would replace this thing called HASL that was a hassle to run.

So the chemistry was installed and I left for lunch while the bath heated up. When I got back from lunch, production was running. The line engineers were overjoyed that the silver covered on the first pass, so they did not feel we needed to run any test parts or analysis before production. (Hopefully my boss is not reading this.) I spent about two weeks in England training the customer and the local teams on how to run this process. I spent hours walking the line, but adjacent to the immersion silver line was a vertical leaded hot air solder level machine. The line was down every third day, and each time the line was shut down, an operator had to physically wedge himself into the unit for maintenance. I could not believe it. I had spent the past six months using a solder pot and a benchtop wave soldering machine, which I grew to respect out of necessity very quickly. I would never shove myself into a machine that runs at such temperatures. HASL requires an exorbitant amount of equipment maintenance compared to other surface finishes and to what benefit?

People will continuously say that there is no one surface finish for every application, and I believe that to be true. Overall, the benefits and weaknesses of each surface finish are pretty obvious. Where we get into trouble is when we stop using the surface finish as a solderability preservative and leave the metal areas unsoldered. With that, the issues of shelf life and environmental resistance become much more important. For this there are two camps: One will say that HASL is the better surface finish choice because it is a thick deposit that will prevent underlying copper from corroding. The other camp will remind the first that HASL has a lot of surface ionic associated with it from flux residue that will promote more surface corrosion. I personally agree with the latter, but also have seen when HASL has not covered pad edges, leaving copper exposed. I have also witnessed small features that did not cover properly on the first pass; the need for a second caused solder mask fracturing and a lot more exposed copper for further corrosion.

So few companies still use HASL that it is probably facing extinction. I know someone just threw the military/medical card. Make sure you are not looking for a last-minute alternative because the fabricator just said they are getting rid of the HASL line to make more room for ENEPIG.

Lenora Toscano is final finish product manager at MacDermid (macdermid.com); ltoscano@macdermid.com.