Today, manufacturers are continually streamlining their products and production lines while improving quality and reducing manufacturing costs. This is especially true in the consumer electronics and the automotive equipment markets where smaller, lighter, and more powerful are the primary constants. To address these requirements, flash-memory components are shrinking in size and becoming more robust and powerful, making them an increasingly popular choice when designing electronic circuits.
Conservative estimates project that flash-memory devices will appear on 40% of all printed circuit boards (PCBs) undergoing in-circuit testing (ICT) by 1999. In fact, flash manufacturers already are seeing the usage grow dramatically and expect even higher numbers overall in the next few years.
Flash-memory components can store erasable data or they can contain upgradable permanent program code. Flash devices containing unique program code offer flexibility in board design by allowing a single board to have multiple personalities.
Flash components can be programmed to their specific function off line and inventoried separately, then delivered to the board assembly area in trays of unique parts. Or, they can be programmed in-line at ICT once the board has been assembled.
With the latter, the same nonprogrammed component type can be placed on any number of different boards. The function of each one depends on the programming it receives. By programming on-board, manufacturers benefit from reduced parts handling and simplified inventory control.
The Flash Evolution
Flash memory is the latest generation of mass programmable memory. From its origins as fabricated, lithographed patterns to once-only, field-programmable ROM, and then to UV-erasable forms, a robust, truly reprogrammable memory has emerged. Instead of being good for only about 100 to 200 programmings and deprogrammings like the UV-erasable ROMs, flash tolerates millions of programming cycles. Flash is faster to test because its programming times are quicker and easier to test because it has more allowable cycles. Logically, it begins to behave like a hard drive.
Before and After On-Board Programming
The newest developments in flash memory include packaging miniaturization such as Intel’s flash memory in a micro-ball grid array (BGA) package with a compact, die-size footprint. These tiny, yet powerful, parts suffer from the usual host of manufacturing issues not specific to flash, such as potential ESD damage and bent leads. Some manufacturers report damage rates as high as 1% or more for flash devices due to preprogramming caused by the extra handling steps required.
Micro-BGAs can be installed using automated surface-mount pick-and-place handling. What better way to gain programming access than on the board itself at ICT? Figure 1 shows an overview of how on-board programming (OBP) of flash memory differs from traditional programming methods.
Before the implementation of OBP, the process of adding flash memory to a circuit board looked like this: A tray of nonprogrammed flash components was delivered to the programmer. After programming, the parts were labeled and added to inventory with their own part numbers. If 50 different versions were created, 50 different part numbers were inventoried, usually as work in process.
When the manufacturing line was ready for the part, decisions had to be made about which part was required, in what quantity, and in what sequence. The correct parts needed to be pulled and delivered to the line and—because they still were in trays—manually placed and mounted on the board. Each version of the board was sent to test and repair and then shipped.
With the implementation of OBP, the process has become much simpler. The nonprogrammed flash components, stored on tape-and-reel, are delivered and added directly to inventory as nonprogrammed flash components with only one part number.
At assembly, the nonprogrammed part automatically is picked and placed on the board. Then, the assembled board is sent to ICT. Once the board is checked for manufacturing defects, the various flash devices are programmed with their specific code.
The different product versions are shipped as needed. This process, which is significantly simpler and more reliable than the alternative, is more cost-effective.
Added Value of OBP at ICT
ICT is beneficial because of its device-specific fault diagnostics and the low cost of repair at this stage of product assembly. The addition of the OBP capability further enhances the value of the in-circuit tester, allowing still more to be accomplished at this step. The significant benefits of OBP include:
Reduced parts damage. Extra handling of the tiny components is eliminated, mitigating major concerns about potential damage. Even proper handling has been known to cause 1% defect rates, far above the parts-per-million rates sought in a manufacturing process.
Streamlined production process. OBP eliminates off-line programming and the additional resources required to support it, such as equipment, floor space, operators, and expensive custom adapters.
Simplified inventory. OBP eliminates the sorting and storage issues of numerous versions of preprogrammed parts. Blank components can be shipped in tape-and-reel rather than trays for manual placement. Separate part numbers and unique device labeling are not necessary. Part numbers are added with the rest of the programming.
Faster product customization and upgrades. OBP makes product customization and upgrades fast and easy. For instance, a single control module might be designed and built, then adapted for different models or various purposes by programming parameters differently. With OBP, multiple board-version assemblies are reduced.
Retention of good programmed parts on failed boards. When preprogrammed flash devices are placed on a board, they become one more component to be tested for process faults at ICT. If a failing board is not repairable, the time and resources spent in programming the device are lost. With OBP, the devices are not programmed and verified until the board has passed ICT.
Just-in-time manufacturing. The capability to program flash on board allows the product to be tailored for specific customers just before shipping. Each board rolling off the line can easily be loaded with different code options.
Flash-Device Programming Methodology
As flash technology advances, new algorithms increase programming speeds by moving more of the programming work onto the chip. Each new generation introduces more sophisticated techniques, such as internal data verification, cell-threshold verification, and queued data-block storage. With these advances, OBP becomes faster, helping the flash programming step fit the beat rate of the manufacturing line.
The basic process sends programming commands to the device data bus, applying the address and data to be programmed, then polling for completion. This is repeated for every address or data segment to be programmed. Each device type will have clear instructions on the programming process.
Understanding these steps and applying only those that are necessary result in the fastest programming times possible. Flash programming adds time to the ICT step, but that time is more than offset by the significant gains in handling efficiency and inventory control.
Worldwide markets are continuing to demand increases in functionality with decreases in the size and cost of electronic products. Making the most of flash memory will help manufacturers meet these demands.
Because flash-programming algorithms continue to improve programming speeds, in-line programming is practical. OBP is superior to off-line flash programmers because it simplifies production processes and reduces component damage and manufacturing costs.
About the Authors
Julie Keahey is an application test engineer for the Manufacturing Test Division (MTD) at Hewlett-Packard. The nine-year veteran of MTD has held various sales and marketing positions. Before joining HP, she was a design engineer at Motorola. Ms. Keahey has a B.E.E. degree from Georgia Institute of Technology. (970) 679-3584.
Copyright 1998 Nelson Publishing Inc.
Mark Bagdy, who has been employed at HP for 16 years, is a product marketing manager in the MTD. He also has worked in a variety of electronics test marketing and management positions, including applications development, training, support, the channel partner program, and new-product development. Mr. Bagdy received a B.S. degree in electrical engineering from the Polytechnic University of New York. (970) 679-2887.
Hewlett-Packard, Manufacturing Test Division, 815 14th St. S.W., Loveland, CO 80537.