DFA demands upfront attention: failure to consider PCB design and production requirements leads to costly loss in time-to-market and time-to-revenue.Design for assembly (DFA DFA - Deterministic Finite-state Automaton. See Finite State Machine. ) is critical to OEMs that outsource PCBs for design and manufacturing. If correctly performed, it shortens the product cycle, minimizes development cost and ensures a smooth transition into production from prototype stages. Unfortunately, OEM (Original Equipment Manufacturer) The rebranding of equipment and selling it. The term initially referred to the company that made the products (the "original" manufacturer), but eventually became widely used to refer to the organization that buys the products and product engineering teams often accelerate design and development cycles, and fail to place emphasis on high volume production considerations such as fixtures, casting or extrusions (FIGURE 1). In cases like these, prototype engineers try to get the product on a test bench quickly to do proof of concept validation rather than emphasizing the DFA considerations.
[FIGURE 1 OMITTED]
The prudent approach is to first examine the volume production considerations. There are different DFA considerations related to prototype assembly vs. production assembly. Each requires a different design skill set and equipment. If the right approach isn't used, costs can escalate and debugging (programming) debugging - The process of attempting to determine the cause of the symptoms of malfunctions in a program or other system. These symptoms may be detected during testing or use by real users. the product will add additional costs as well. At prototype levels, validity of the circuitry and functionality of the board is far more important than the testability and manufacturing guidelines that are necessary to implement at the production level in order to make production smooth and flawless.
First article approval of the PCB PCB: see polychlorinated biphenyl.
in full polychlorinated biphenyl
Any of a class of highly stable organic compounds prepared by the reaction of chlorine with biphenyl, a two-ring compound. is the most important step toward effective DFA. An OEM approved first article PCB proves valuable in answering all questions relating to relating to relate prep → concernant
relating to relate prep → bezüglich +gen, mit Bezug auf +acc manufacturing, assembly and test. It is the "proof of concept" before a PCB order goes into production, even if quantities are small. For the OEM, a smooth transition to production means key market demands such as time-to-market, quality, reliability, product delivery and critical time-to-revenue are met.
Multiple Team Interaction
DFA relies heavily on multiple team interaction. Design, fabrication fabrication (fab´rikā´shn),
n the construction or making of a restoration. , assembly and procurement teams assigned to a given PCB project must precisely tune into a project's specifications. Design engineers must be fully aware of certain assembly aspects, and likewise, assembly engineers must understand a project's design in detail. These teams need to know the particular areas that make assembly and testing go smoothly. They also need to anticipate problems that can arise at production levels and in the field, and should be able to resolve these issues quickly.
Working in tandem Adv. 1. in tandem - one behind the other; "ride tandem on a bicycle built for two"; "riding horses down the path in tandem"
tandem , these teams can address and resolve most of the issues and questions at root cause levels. For example, if the design team is specifying a component that has a much-extended lead time, let's say 12 weeks or more, the procurement team and designers can flag an issue and suggest a replacement component that is readily available in the marketplace.
To design a good product that has implemented DFA, the following considerations must be addressed:
Adequate test points should be deployed across the board to have complete access and coverage during flying probe or ICT (1) (Information and Communications Technology) An umbrella term for the information technology field. See IT.
(2) (International Computers and Tabulators) See ICL.
1. (testing) ICT - In Circuit Test. test or for direct probing (FIGURE 2).
[FIGURE 2 OMITTED]
When fabricating a board, consider panelization vs. fabricating one board at a time. This is especially beneficial when the board size is relatively small, such as 30 in. (2) or less. Panelization increases the speed of fabrication and assembly of the product, thereby reducing costs for OEMs (FIGURE 3).
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While placing the components at the layout stage, it will be prudent to use one side of the board vs. utilizing both sides, if possible. Placing components only on one side reduces NRE (Non-Recurring Engineering) Refers to the cost of creating a new product, which is paid up front. Contrast with "production cost," which is ongoing and based on the quantity of material produced. costs at assembly and test stages, plus it speeds up the component placement at the pick and place machines and reduces the testing time of the components. Placing components only on the top also reduces re-work, QC and debug To correct a problem in hardware or software. Debugging software means locating the errors in the source code (the program logic). Debugging hardware means finding errors in the circuit design (logical circuits) or in the physical interconnections of the circuits. times, all of which results in reducing assembly costs.
All the mechanical considerations should be kept in mind at the PCB design stages for DFA considerations such as designing at least two, if not three, mounting holes for the PCB and clearly defining the polarity (1) The direction of charged particles, which may determine the binary status of a bit.
(2) In micrographics, the change in the light to dark relationship of an image when copies are made. on the polarized A one-way direction of a signal or the molecules within a material pointing in one direction. components. This practice eliminates any confusion that may arise at component placement, testing and debugging stages.
For specifying components at design stages, engineers should use the components, which are time tested and verified, as much as possible. Doing this will reduce debug and test times, as well as make the product more reliable and predictable. Effective DFA also calls for using commonly available components with specifications and features already proven in other system applications.
If you are using custom components, you are at the mercy of one or two suppliers whose production times are dependent on their capacities and production levels, and the delivery time can easily shift to a later date. Since there's a chance custom components may not have been used by other customers, they may not have gone through the test of time and application, causing potential latent defects in the field that the OEM may not be aware of.
Aside from using standard components, another major consideration involves careful monitoring of equipment-related features and physical tolerances. For example, take the drilling machines used during the fabrication process of PCBs. The drilling process is known to have some wander. Wander outside of the established tolerances will have a negative impact. DFA demands that tight tolerances are maintained in this regard, especially in smaller hole sizes; under 10 mils. Also, it is important to maintain proper alignment of multiple symmetrical components In electrical engineering, the method of Symmetrical components is used to simplify analysis of unbalanced three phase power systems.
Charles Legeyt Fortescue in a paper presented in 1918 ( . If modular designs are involved, keep all modules alike so that when an IC is placed in one module, similar ICs are identically placed in the second, third, fourth and so on. In the same way, resistor resistor, two-terminal electric circuit component that offers opposition to an electric current. Resistors are normally designed and operated so that, with varying levels of current, variations of their resistance values are negligible (see resistance). and capacitor networks must be similarly placed to reduce SMT (1) (Surface Mount Technology) See surface mount.
(2) (Station ManagemenT) An FDDI network management protocol that provides direct management. Only one node requires the software.
SMT - Station Management machine programming and placement time. In some cases, a PCB may be odd-sized or shaped. Hence, this particular feature is made clear at the outset in DFA so that when the required fixture is used in the assembly process its limitations are specified upfront.
For mixed signal designs, a clear cut strategy should be defined to reduce noise to signal ratios, power and ground signal should be properly defined according to according to
1. As stated or indicated by; on the authority of: according to historians.
2. In keeping with: according to instructions.
3. the component placement, and shielding of high-speed digital signals should be incorporated. If these strategies are not implemented for DFA at the layout stage, product would create unacceptable noise levels and may need a redesign, costing more time, resources and money.
An experienced PCB layout team properly places components on the board at layout stages, keeping in mind electrical characteristics, heat dissipation Noun 1. heat dissipation - dissipation of heat
chilling, cooling, temperature reduction - the process of becoming cooler; a falling temperature and noise generating aspects of the components. For example, on a board that has analog and digital sections analog components are clustered together in a module and digital components are placed in a different segment of the board, with their respective power and ground planes properly placed underneath the component for a clean and quiet signal (FIGURE 4). Furthermore, DFA addresses such aspects as electrical characteristics, analog and digital PCB sections, and high vs. low frequency components.
[FIGURE 4 OMITTED]
Efficient product design provides the OEM with a competitive edge. It results in faster product delivery than a design using custom components and inadequate DFA, which can sometimes incur 8 to 14 weeks of delay, for procuring these components. Moreover, sound DFA speeds the product through assembly, as well as makes rework re·work
tr.v. re·worked, re·work·ing, re·works
1. To work over again; revise.
2. To subject to a repeated or new process.
n. and field serviceability (system) serviceability - The ease with which corrective maintenance or preventative maintenance can be performed on a system (e.g. by a hardware service technician). Higher serviceability improves availability and reduces service cost.
Serviceability is one component of RAS. easy.
The bottom line is that properly executed DFA can save the OEM 10-30% of the pick and place, and testing and debugging time, which translates to major cost savings. A poorly designed product or one that uses nonstandard non·stan·dard
1. Varying from or not adhering to the standard: nonstandard lengths of board.
2. parts and processes will take more design and assembly time, incurring greater costs in manufacturing. Conversely, DFA techniques based on standard, proven components and practices will maintain lower costs and make the process smoother.
ZULKI KHAN is president and founder of NexLogic Technologies Inc. He can be reached at firstname.lastname@example.org.