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The Knowledge Base: A CM’s Perspective on Box Build Practices

In the ever-evolving landscape of electronics manufacturing, the box-build process stands out as a critical phase that bridges the gap between individual component manufacturing and the delivery of a fully functional electronic system. This intricate procedure, encompassing the assembly of everything from PCBs to wire harnesses and mechanical enclosures, demands a high level of precision, efficiency, and innovation. As the electronics assembly industry expands and diversifies, understanding the best practices within box-build assembly has become paramount for manufacturers aiming to stay ahead in a competitive market.

In this column, I will delve into the subject of box-build best practices within the electronics assembly space. These conversations will explore the nuances of systems integration, focusing on the strategies industry leaders employ to navigate challenges such as supply chain management, quality control, and technological advancements.

To discuss box-build best practices, I invited Allison Budvarson, COO of Out of the Box Manufacturing (OBMFG), a contract manufacturer in Renton, Washington, and Chris Denney, CTO of Worthington Assembly, a contract manufacturer in South Deerfield, Massachusetts, to provide insight on box-build best practices based upon their experience and company protocols.

Through this interview, we aim to shed light on the methodologies that have proven successful in ensuring that electronic assemblies are not only built to the highest standards but also aligned with the evolving needs of consumers and industries alike.

Can you walk us through a complex box-build project your company worked on? Specifically, detail how your company addressed any technical challenges that arose, including any innovative solutions you implemented to overcome them.

 Allison Budvarson: OBMFG recently went through an NPI build for a new and very complex box-build assembly, which included several densely populated PCBAs, wire assemblies, mechanical assembly, and test requirements. This is a project we have been working on with our customer over several months, which started with building the PCBAs and then moving to box-build.

We’re unique in that we offer a dedicated work cell for our customers to utilize during an NPI, so that we can work side by side with them on our shop floor during product realization. In this case, when it came time to assemble the box-build, the customer spent a week in our facility with us, assembling the first articles and working through test while we created assembly documentation and set up a 5S work cell to accommodate production qualities in the future. One of the challenges in a project with this many subassemblies and assembly steps was how and where to insert inspection and test points to accomplish the most efficient and high-quality assembly process.

Chris Denney: We don't really get involved in anything I would call a "complex" box-build. Most of the box-build we do is small enough to sit on a workbench, nothing larger than a VCR. (Does anybody even know what those are anymore?)

I recall working on this one particular box build that involved two circuit boards sandwiched together and then crammed inside a small plastic case about the size of an iPhone. All the components on this board were through-hole components and included a large serial port that the end user would interface with. Because of the thinness of the plastic case and the fact that two circuit boards were being sandwiched together, it required us to cut all the through-hole pins flush to the PCB and fold other devices flat to the board to keep it compact enough to fit into the case. The design was so old that the customer was forced to ship serial-to-USB adapters with each order they sent to customers. It also used rectangular LEDs to provide feedback to the user, but these rectangular LEDs were very difficult to align with the plastic case's overlay.

Being that it was all through-hole, it was already time-consuming and expensive for us to assemble. We asked the customer if they would be interested in changing the design to use surface mount devices, but all their engineers had either left for other jobs or retired. We decided to take on the task ourselves instead. We redesigned it with all surface mount devices (except for the LEDs), got everything to fit onto a single PCB, and changed the serial port to a USB port.

The last thing we tackled was getting the LEDs to align to the overlay properly without fussing around with them. These LEDs needed to be through-hole as they had to stand off the PCB and push through the plastic enclosure's cutouts to align properly with the overlay and provide feedback to the end user. To make this easier, we created a “poka-yoke” device that held the LEDs in place while we soldered them. It made it impossible to get their height or their alignment incorrect. So, by the time we put the PCB into the enclosure, they fit perfectly without having to adjust their alignment first.

Explain the steps from receiving a box-build project’s specifications to the final assembly and testing phase. How do you ensure that all components, such as PCBs, wiring harnesses, and mechanical enclosures, integrate seamlessly?

Budvarson: We always start with the relationship. Our business development and technical sales teams begin by meeting with the customer to gain a well-rounded understanding of the assembly as well as the customer’s goals and timelines. From there, we gather documentation, build a quote and assembly docs, create necessary fixtures, and plan the work according to the customer’s delivery needs. We generally batch the various subassemblies and ensure they all meet quality requirements prior to beginning the box-build. As in the previous example, a customer can visit us to see how things are working as we begin assembly and spend time close to the project.

Denney: Box-build is a journey, not a destination. Your initial look at the project will result in dozens of questions. Those will then lead to more and more questions until, finally, your customer goes away and finds somebody else who will do it for them. We don’t bother with any of that nonsense. We look at what the customer is trying to accomplish and discuss building a small quantity of units first; it’s typically no more than 50 pieces.

We are upfront with them that there will almost certainly need to be changes made to the design based on this initial build, and we make sure the customer is open to working together with us on this. We give our customers a maximum price we'll charge them for the box-build, with an agreement that we'll learn from this to provide a more accurate quote. If it takes us longer than expected, we eat that cost. But if it takes us less time, we'll offer them credit on a future order for that value.

Once we sit down to actually perform the build, we note down what does and doesn’t work, , and what needs to change. We may have to do this for a couple of revisions, depending on how close the engineers got in their initial design until we can finally provide a fully accurate quote from a process that we're happy with.

Describe your experience with quality control in box-build assembly. What testing protocols do you implement to ensure the final product meets both the industry standards and customer expectations?

Budvarson: First articles always receive 100% inspection to validate workmanship prior to shipment. For in-process inspection, we build appropriate inspection points according to each manufactured assembly. Assembly personnel generally work in a cell formation, so each person inspects the work done by the prior person before moving on. We also look back at captured quality data regularly to identify areas for improvement and training. Test is customer-directed and usually requires working with the customer to create the fixture, program, and procedure to meet their individual needs.

Denney: IPC has standards for circuit boards and wiring harnesses, and we train and certify our staff to follow these standards. We inspect all the subassemblies to make sure they meet the standards before installing them into the final assembly. Oftentimes, the final product itself will have a built-in diagnostic mode where we can test all the product's functions before delivering it to our customer.

In your experience, how have you managed or collaborated with suppliers to ensure the timely and cost-effective procurement of components necessary for box-builds? Can you give an example of a supply chain challenge you faced and how you resolved it?

Budvarson: Metals can present a challenge. In one instance, we had a box-build customer that was ordering sets of parts, with 23 pieces making one set. If one piece is non-conforming, you obviously have a problem. Lead times for sheet metal and fab shops can also drag out assembly delivery, especially when it includes paint or other special coatings. Usually, box-build jobs will push us to a customer-directed source as well, so we’re managing a new product and qualifying a new vendor simultaneously. It’s a challenge but something we’ve done many times over the years, so we’ve got a good base of knowledge from which to work.

Another challenge with this type of situation is that customers may want to consign these metal pieces. In this case, we end up with drop-shipped components. We still need a vendor relationship with the fab shop, but a relationship with the customer is critically important to ensure that we receive what we need in a timely manner and keep them informed on both on-time delivery and quality of drop-shipped materials.

Denney: Are you kidding me? We're constantly managing this. It never ends. Time is your friend here, so the earlier you work with suppliers to give them dates and quantities, the better. One supply chain challenge we had, as it specifically relates to box-build, was working with an injection molder who regularly had challenges delivering product on time to us. We had a conference call with them and learned that there was basically just one person in the company who could set up the injection molding machine and run the first few samples before they could proceed with production. We calmly but firmly insisted that they train and/or hire additional staff to help with this. They agreed and committed to making the change and have since turned into one of our most reliable suppliers.

Discuss how you approach project management within the context of a box-build assembly. How do you coordinate between different teams, such as design, procurement, and assembly, to ensure the project is completed on time and within budget? Can you share an instance where your company’s leadership directly contributed to the success of a project?

Budvarson: OBMFG has always been successful because of the expertise and teamwork of our incredibly talented personnel. Generally, management team members from purchasing, manufacturing, quality, engineering and technical sales come together during the NPI phase of a complex box-build project. We also have an immensely talented lead in the box-build cell that is an integral part of the process. We utilize our planning and assembly processes to ensure things get done. When something doesn’t work, we utilize our CAPA process to find root cause and validate our solutions to ensure they have the intended result.

Denney: That's just called "doing business." We use our MRP software to manage the supply chain and drive the assembly process to deliver to our customers. The harder part was managing demand expectations. How much of what was needed and when? This is largely in our customer's hands, and most people would stop there. But last-minute orders that take weeks to prepare for aren't rare, and nobody's happy about it. Not us, and certainly not our customers.

We invited one customer to visit us and showed them our process for assembling their products. We were able to show them how long each product takes to prepare, and all the various steps involved in getting the subassemblies ready for the final assembly. We then proposed using a shared online spreadsheet so that we could track their in-stock inventory, along with our "ready-to-ship" inventory. This provided much greater visibility into each other's shops. We could easily see their demand, and they could easily see our supply. If we notice a sharp drop in their stock of any one product, we should make sure we're building more of that product. If they notice our ready-to-ship inventory is low, they can give us a heads-up that they will soon need more and that we should get ready. This smoothed out the whole process. No more surprises. No more overbuilding and holding inventory longer than we need to. We're happy, our customers are happy, and our suppliers are happy. I think Michael Scott would call that a win-win-win.

This column originally appeared in the April 2024 issue of SMT007 Magazine.