Circuits Assembly Online Magazine - Prototype vs. Production Outsourcing

News

What to look for may vary by geography. Tips on what, and who, to audit.

When it comes to outsourcing PCBs, OEM procurement staff must fully understand the differences and nuances associated with prototype and production manufacturing, regardless of where those services are situated. Procurement from overseas sources has additional criteria to those standard for domestic procurement. However, requirements for high quality, tight delivery schedules, local EMS representation, up-to-date technology, modern equipment and well-trained personnel are common threads to procurement personnel across all regions and EMS tiers.

Prototype and production procurement should be kept separate because they are different (Table 1). A prototype engineer focuses on quick delivery to achieve time-to-market. Designers want proof-of-concept upfront to determine how a product performs. It is okay if the product operates at, say, 50 to 75%, and designers are not overly concerned if some of the product’s features fail to work the first time.

Table 1

Prototype shops differ in several respects from production shops. One area is turnaround time. Standard turn, also known as extended turnaround time, refers to the period between order entry and finished prototype, and differs among suppliers. “Standard” turn could run from one to three weeks. This should be contemplated thoroughly, as an OEM could incur extra costs and miss market opportunities if an expected three-week delivery stretches to six to eight weeks.

Prototype line traits. A prototype line must be flexible in terms of accepting boards of different sizes and complexity levels. Prototyping for both PCB fabrication and assembly is, in effect, R&D since the product is not yet mature. Prototyping is characterized by a number of design changes involving specifications, features and countless product aspects. For instance, a reprogrammable FPGA’s power and ground pin-outs may change to comply with different power and voltage requirements on a PCB. Or strip planes between analog and digital sections may need to be changed, depending on the impedance control requirements on the board.

By nature a prototype incurs constant change, up to and including the day it gets shipped. The OEM may change a resistor or capacitor value, for example, just before the product leaves the factory. Flexibility should be embedded in the process and procedures from design to assembly. At times, 100% review may not happen due to time constraints, as the OEM skips intermediate steps to rush the product out the door.

An easy-to-use GUI is important to help technical staff quickly reprogram prototype line systems. In doing so, the EMS provider can easily and quickly execute a changeover to a new prototype job. Reprogramming should take no more than a few hours, so that multiple jobs can be executed on the same prototype line on any given day. Easy prototype programming is important because prototyping requires quick format changes to maintain a steady and smooth flow of other incoming jobs.

A prototype line demands the latest technology available, including AOI. If a fabrication shop is involved, it is important to know the kind of innerlayer inspection and lamination registration and verification tools and capabilities used during the fabrication process. It is also important to know the fabricator’s maximum layer count capabilities and how it builds complex boards.

A proactive sales team plays a major role in a highly successfully prototype line because it acts as an early warning system to advise the OEM of potential issues, concerns or questions. Being alert to possible problems ensures that a prototype project stays on track and on schedule.

Technicians should be multitaskers, capable of maintaining a smooth prototype line and moving from one project to the next. While the prototype SMT machine is running one job, technicians should be programming the next job offline, changing the feeders and so on. Hence, a set of two SMT machine operators are working multiple jobs in tandem.

Finally, successful prototype lines require the right equipment to support the latest technology prototype projects. This includes an SMT line that is easy to program, AOI, a paste height inspection system, a flying probe tester and BGA/CSP installation capability. Such equipment ensures that jobs can be efficiently and successfully performed. Along this line, it is important to know the capacity an EMS provider offers and its limitations.

Production line traits. A production line has completely different traits. The main focus is test coverage, to ensure the PCB being produced is fully tested according to OEM specifications. This can include functional test, flying probe and in-circuit testing to ensure test points are allocated at different critical locations on the board. Also, fixtures and tooling for SMT, wave soldering and in some cases flying probe test must be in place to run the product quickly through the production cycle. Well-defined production procedures call for embedded quality control steps. It is important to set a self-correcting course while the product is built.

Production lines are geared for running the same product over a long period of time. Quick changeover time, easy-to-use GUI and programming time are not critical factors. When a product is placed in production, established procedures operate for the duration of the production run and require minimal maintenance.

Sometimes, an OEM product takes a few months to upwards of one to two years before justifying large volumes for overseas production. Production runs of 500 to 5,000 on a yearly consumption basis are not normally acceptable for moving to low-cost regions for production. As such, OEMs should always consider local EMS providers that can perform both prototype and small production runs.

In some cases, production runs must remain with U.S.-based EMS providers, either due to technology levels or legislative restrictions. For example, products intended for defense programs are restricted by law from being built overseas.

Prototype fabrication. The ideal prototype fabricator can turn product within 24 to 48 hours, as required. It possesses the technology to build boards with fine-pitch BGAs and CSPs and turns out cutting-edge PCBs with finer capabilities. This means fabricating boards with 0.003" lines and spaces, and with BGAs with 0.5" pitches. The shop audit should look for equipment such as laser drills (for hole sizes of less than 0.005"), a full selection of surface finishes (immersion silver, immersion gold, OSP and HASL) and the ability to produce hybrid boards with mixed layers of FR-4, polyimide or Teflon materials.

Special considerations like sequential lamination and controlled-depth-drilling are equally important. This calls for special tools and techniques to comply with prototype needs specific to different industries and applications. Sequential lamination, for instance, involves laminating board layers in pairs, one pair after another, rather than laminating them all at once. Controlled-depth-drilling deals with forming holes by drilling from the top layer to a specific depth (but not all the way through the bottom side of the board).

The flying probe tester’s speed is another important aspect. Does the fabricator have a four- or eight-head tester? Is it a one- or two-sided flying probe tester? Testing speeds are crucial to prevent bottlenecks so that the fabricator can churn multiples of products at a time. Further, is the technology available for catching and inspecting inner layer registrations? This is especially vital for multi-layer (10 or more layer) boards. Inspect and evaluate internal layer registration to prevent misaligned layers.

Production fabrication. For production fabrication, the customer should look for criteria such as standard turn time, aspect ratio and other process-related capabilities such as board complexity, layer counts, surface finishes, sequential or multiple laminations and others.¹ Standard turn, as mentioned, is also determined by board complexity. A two- to 10-layer board, for example, has a standard turn of a week. However, a 12- to 20-layer board may have a two-week standard turn, while a 20- to 40-layer PCB will typically take three weeks. Based on this variety of standard turn times, it behooves an OEM to specifically ask the EMS provider for its definition of a standard turn for a given board for both prototype and production runs.

Prototype assembly. Selection criteria for prototype assembly includes capabilities for efficiently handling fine-pitch BGA and CSP devices, hand-loading to avoid programming charges, especially for small (one to 10 pieces) quantities, the ability to perform consigned or turnkey assembly, inventory management control, top-notch test capabilities, component procurement capability for smaller and larger BoMs (plus the ability to cross-reference the parts, which may include hard to find and obsolete items).

The flexibility to perform machine vs. hand loading is important because the project may deal with small quantities involving moderate technology where it may be easier and faster to hand-load. A prototype assembler should have the flexibility to perform either turnkey or consigned assembly work, as different projects and customers have different needs.

Production assembly. The OEM mindset for production assembly involves a number of considerations. Those include design for test (DfT) and design for manufacturing (DfM), updated documentation, written diagnostic tests and macros, tester limitations and written troubleshooting guidelines, among others.

In terms of DfM, if board fabrication is involved, panel size utilization for maximum yields is important, especially if the board is odd-shaped. When multiple boards on one panel are run through pick-and-place, wave, wash and test, fixtures are needed. The panel must be designed to be assembled efficiently to prevent waste during fabrication. Plus, there should be the right and final balance between the number of boards placed on a panel and the amount of time required to perform pick-and-place or test.

Similarly, DfT needs to be incorporated into production assembly. This involves, among other things, situating test points evenly across the board so that all areas are accessible by test probes. Maximum accessibility should be made on the board for debugging and testing. If it is a mature product, investing in a special jig or creating special equipment may be wise to make production run smoothly and error-free. An OEM can amortize the value of that special jig or fixture over the product’s lifetime. Fixtures are expensive, but can slash handling time vs. manual handling methods, giving OEMs major savings.

When a product comprises multiple PCBs, a test mechanism should be implemented to test the full functional system as well as individual boards. Unless boards can be tested individually, considerable time is incurred to run system testing to isolate and debug a fault. Also, for production assembly, a troubleshooting guideline should be produced for test technicians. Guidelines for production quantities should be clearly defined and stated, and explained in simple language.

Efficient production assembly also places considerable attention on testers and their limitations. Targeting the proper test strategy for a given product is crucial. For instance, flying probe may be sufficient for a board with relatively few (e.g., 25 to 100) components. On the other hand, a board populated with 1,500 to 2,500 components demands proper ICT, with fixtures in place. Troubleshooting guidelines, diagnostic tests and associated documentation must also support ICT.

Going Abroad

Offshore production fabrication. At a certain point, it makes sense for an OEM to go overseas for production fabrication. Some overseas fabricators look at dollar volume to qualify a production job. Others qualify it in terms of panel count. A small shop may consider 25 panels for production, whereas larger shops may not accept anything less than 200 panels.

Production lead times run about 4 to 6 weeks for up to 2,000 boards and about 6 to 8 weeks for 10,000 to 20,000 boards. The most important aspect is to ensure the shop has regional (e.g., U.S.) representation, which means that there is a local representative available to resolve issues. Shop capability is also key in the selection process. Taking time to visit and qualify an offshore production shop will pay big dividends in successful project completion.

As for RMAs, it is prudent to have a backup plan to avoid spending extra thousands of dollars to return faulty products. This is when the local representative proves valuable. Most often, the overseas firm will produce new PCBs to replace RMAs. Some overseas fabricators have local partners that produce those replacement boards, which is an ideal scenario.

Offshore production assembly. Offshore production assembly is another story. The OEM should recognize that EMS firms overseas often use different, albeit similar, materials and components made for their local markets. In this regard, when component shortages occur, the OEM must make sure the EMS has sufficient clout to obtain allocated product.

Chinese and Taiwanese components have different designations and manufacturers than U.S.-made components. U.S. parts are therefore replaced with overseas devices of equal or similar value. Generally, no issues are involved as long as the OEM product is mature. However, if the need to debug arises, the new or unusual components could pose an issue.

OEMs also have to consider lead times, which could extend to 16 to 20 weeks. Local holidays have to be factored in. For example, do not expect work or even communications to take place during the 10-day Chinese New Year. OEMs should carefully evaluate the EMS company’s test prowess, and look into any nonrecurring engineering (NRE) charges, which can run into multiple thousands of dollars.

What if the OEM is introducing a new, U.S.-made component in the PCB assembly? The OEM has to receive assurances that those new components will be shipped expeditiously and arrive at their overseas EMS destination on time, and not held up at customs or buried in red tape. The OEM must also get a handle on duties or other forms of taxation.

Notes

Aspect ratio refers to board thickness versus the smallest hole size on the board. For example, an 0.008" hole drilled on a 0.125" thick board has an aspect ratio of 14:1. Aspect ratios of 12:1 or higher are make the board difficult to fabricate because the tolerance of the drills limits the ability to make small holes on thick boards.

Zulki Khan is founder and president of Nexlogic Technologies Inc. (nexlogic.com); zk@nexlogic.com.