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Chihuahua Facility Works Smarter Through Lean

SigmaTron International’s facility in Chihuahua, Mexico has been applying Lean Manufacturing principles holistically for over a decade.

“The majority of the management team at the Chihuahua facility has been together for 19 years. There have been different names on the door during that time period, but the team and the operational improvements they have made have stayed constant,” said Peter Sognefest SigmaTron’s General Manager and Director of Operations for its Vietnam and Chihuahua facilities.

Not surprisingly, those operational improvements aligned well with SigmaTron’s existing systems.

The Chihuahua facility started its Lean journey in 2002. One area of focus was improving line changeover time by migrating from paper visual aids to electronic work instructions displayed on monitors at each workstation. This not only enabled fast line changeovers; it also ensured documentation integrity and gave production operators a higher quality visual aid. Today, that system has grown into an internal Manufacturing Execution System (MES) system that links with capabilities already in Agile and also interfaces with SigmaTron’s proprietary iScore system. Product is bar coded and tracked through each operation. Real-time production status monitors display data in each work area, so production personnel are aware of actual production vs. targeted goals. Should the headcount of a manual assembly line change, due to an increase or reduction in demand, the electronic work instructions automatically adjust the number of parts assembled by each operator. This system can also switch programs in SMT and on some test equipment. This helps speed changeover, plus ensures the correct set of process steps is performed on each work order. It also provides the level of traceability needed to quickly analyze root cause and implement corrective action should a product failure be detected.

The facility has seven SMT lines. Five utilize Universal equipment and the two newest utilize Yamaha equipment. The Yamaha equipment uses a cart system and extra feeders have been purchased to enable multiple jobs to be loaded onto each cart. Yamaha’s software determines which feeders are used for which production lot. Offline setup further optimizes line changeover time when carts must be changed out. One of the challenges the facility faces is customer requirements to supply spare parts for products that have been out of production for as long as 15 years.

“All spares are built on one of the new lines, because the Yamaha software makes it easy to cut in a short production run with minimal changeover time,” said Jose Luis Garcia, the facility’s Plant Manager.
Production efficiency is also enhanced by a cross trained workforce capable of moving among lines as demand varies.
Another area of efficiency improvement has been test. The team makes many of its own Labview-based functional testers and has worked to improve its standardized platform.

“We have changed our design to utilize a shelf-based design with a vision system on the bottom. We found that clamshell fixtures had too many mechanical parts that would wear out quickly in high volume production. Our shelf fixtures are faster to load and have less wear,” added Garcia.

Lean philosophy also influences end of the line activities. The shop floor control system provides a strong check and balance in this area, because a barcode scan at each operation step determines whether or not all necessary prior steps have been completed. Programming is not integrated with test because, in most cases, it can be done faster as a separate operation than when integrated into a test program. Test is integrated with packing and the shipping label is printed after a bar code scan verifies that the unit has passed test plus completed all prior steps.

The facility uses kanbans both in production and in finished goods. The shop floor control system uses a graphical illustration of bins to share production schedules, making it easy for all production personnel to understand production status and requirements.

Finished goods kanbans are held a warehouse in El Paso, Texas, to eliminate any added lead-time or cost associated with border crossing. Bins have been sized to customer requirements and are replenished as inventory is pulled.

The results speak for themselves. The Chihuahua team has not had a shipment rejected by a customer in over seven years.

Suzhou Facility Helps Improve Test Efficiency and Coverage

SigmaTron International’s test engineering team in Suzhou, China routinely helps customers reduce the cost of test while achieving their test coverage goals. Nearly 80 percent of their projects utilize SigmaTron-designed fixtures and/or functional test equipment.

The team’s formula is: “keep it simple and focus on what is needed.” Programming is done utilizing C# and Basic Language, using RS232, USB, GBIP, etc. to communicate to test instruments, read back the test data, analyze data, transmit the test result to the terminal and then store the test result in the network database.

“The more complex the programming language and development environment, the more time test can take. For example, if the team used C++, the program would have to compile it with the overhead, which adds time. There is not much overhead and fancy interfaces in our programming environment. Our goal is load data in and read it out as quickly as possible,” said HomMing Chang, Vice President China Operations.

The test engineering team can design a test program from a functional specification or even create a simple functional test from a schematic alone. They prefer to design clamshell hold down fixtures or a bed of nails fixture, as connector-based test can weaken the connector and exceed target test time. They have a standardized functional test platform and can design equipment that does everything from simple functional test to a program, test and pack station.

One driver of this strong internal capability has been difficult to replicate failures in customer-supplied test equipment.

“Many customer-developed testers have design issues or simply aren’t up to the rigors of volume production. The problem is typically good contact isn’t being made with the unit or the test program isn’t measuring the signal at the right points. This causes intermittent failures that can be hard to replicate. When there is a trend of units that fail a test, but pass the second time, that is often a clue there is an issue with the tester. In those cases, we will make fixtures or jigs to improve the contact and see if that changes the trend. If it doesn’t the issue is normally software-related,” Chang added.

For example on one project, SigmaTron was performing functional test at the end of the line and the customer was performing system test at their factory. Units that passed functional test were failing system test. SigmaTron’s team worked with the customer’s team to understand the detail of the failure enough to replicate the failure. The end result in this case, was that the signal in the system test wasn’t stable and there needed to be design modifications. Most test programs take a signal reading a couple of times during the test and average out the results. However, if the signal isn’t measured at the right time it causes a failure. Reprogramming the tester to optimize the timing of signal measurement can eliminate the problem.

Another trend the team is seeing is a customer focus on genuine first pass yield data.

“Customers want to know if units passed the first time they were tested. Providing this information is relatively easy to do since we use bar codes with serial numbers on all our products and track them using our Tango shop floor control system. We are also able to support real-time test data sharing with customers who require it,” said Chang.

This focus on data collection is one reason the test engineering team prefers to design test fixtures even when utilizing customer-supplied testers. They typically design a clamshell press down automated fixture which will access test points vs. make contact through a connector. When SigmaTron’s team designs a fixture, they set it up to make sure all necessary data is stored in the database as units are tested. Comparatively, customer-supplied fixtures don’t always have this capability built in. In these cases, SigmaTron can utilize an interface program with tester’s computer to (Continued from page 2)
add the data collection capability.

Minimizing test time is also a focus. In one case where the customer-originally supplied a connector-based fixture, the test time was one minute and the handling time was six minutes. Test engineering designed a clamshell hold down gate with a pogo pin to establish contact with the connector along with a probe plate that allowed the tester to be actuated from either top or bottom. They also modified the programming to make it more stable, as the test program was not measuring voltage at the right time. The end result was still a one minute test, but handling time was reduced to 30 seconds.

“We find that customers are often amazed to see this level of test expertise in China. In some cases, they’ve even had us fabricate duplicate test sets and fixtures for their factories,” Chang added.

Design Alliance Speeds Product Development, Cuts Cost

SigmaTron International supports its customers’ product development requirements both through its internal Spitfire Controls design team as well as through strategic alliances with independent design firms. In Union City, an alliance with Infinite Vision has resulted in several project wins. Infinite Vision is headquartered in Scotts Valley, CA, but also maintains office space within SigmaTron’s Union City facility to support collaborative product development efforts.

In 2014, Infinite Vision and SigmaTron teamed on a consumer product that is now in volume production. The project illustrates the benefit of a close working relationship among the customer, design firm and electronics manufacturing services (EMS) provider.

Infinite Vision developed the product design with input from SigmaTron’s team on best materials options. During this analysis, SigmaTron’s International Purchasing Office (IPO) evaluated fabricated component suppliers as part of an initial approved vendor list (AVL) audit. The customer had originally specified a motor manufacturer in Asia. The IPO team found that what looked like a high volume motor manufacturer on the web was actually a very small operation not capable of building the volumes likely required for production. As a result, a new supplier was identified and the design was modified to accommodate that motor prior to any tooling being fabricated.

Prototypes were manufactured in September 2014. The project was then transferred to SigmaTron’s facility in Tijuana, Mexico where a pilot run of 200 units was performed later that month. A 2500 unit pre-production run was done in December 2014 and product went into volume production in 2015.

SigmaTron’s robust new product introduction (NPI) process helped address the challenges associated with bringing this new product to market, including supporting several engineering change orders (ECOs) driven by changes in product accessories. Infinite Vision developed a manufacturable design and SigmaTron’s team also performed a design for manufacturability (DFM) review which made some additional recommendations.

Design for testability was also evaluated. The goal was to create a robust verification process with as much coverage as possible. At the same time, customer preferences for cost of test were also considered in determining the best mix of inspection and test methodologies. In this case, an integrated program, test and pack station was developed. Since the
product connected to the internet, a record of unit serial number and MAC address needed to be stored in a database accessible to the customers’ support team.

SigmaTron also provides a number of post-manufacturing services including fulfillment through its distribution center in San Diego and repair depot in its Tijuana facility.

The end result was a cohesive product development and NPI process which eliminated issues prior to their impact on volume production. The customer has a one-stop support option supporting the entire product lifecycle and can focus its team’s energies on marketing its products.

SigmaTron Featured in Several Publications in Q1

Several SigmaTron International-related articles were published in Q1 2016. In January, an article on trends in medical electronics contract manufacturing included discussion on some of trends SigmaTron’s team is seeing.

A Circuits Assembly article in January discussed best ways to optimize operational efficiency as business grows. A March article in Circuits Assembly discusses the Tijuana facility’s Lean approach to repair depot.

MDM West Is Big Success

SigmaTron International exhibited at MDM West in Anaheim, CA in February.

“We had a great show with a lot of attendees visiting our booth all three days of the show. There was significant interest in our ability to support products from product development through fulfillment to end markets. The fact that we had good success stories we could discuss in detail, generated strong interest,” said Curtis Campbell, Vice President of West Coast Sales.