February, 2016
www.us-tech.com
Saving Valuable Time in SMT and Test Programming
By Michael Ford, Mentor Graphics I
t can take many days for a team to prepare a line for production. First, information is gathered.
This includes the details of each placement, test and inspection requirement. The data are often col- lected in a mass of different formats, both digital and physical, as a designer tries to represent the gener- al layout of the PCB to the engineers on the assembly floor. Next, the engi-
The engineers who
piece together product information must change their perspective and adapt to a new field of manufacturing. The sheer number of systems
aggravates the challenge of data entry.
neering team has to enter it, without a single mistake or omission, into each of the several systems used in the assembly process. The line often incorporates one or more SMT plat- forms, printing, automated optical inspection, solder paste inspection, manual inspection documentation, and in-circuit testing. The sheer number of systems
aggravates the challenge presented by data entry. The process of enter- ing and checking information in each system is different, as are the library parameters that define the size and shape of materials. Every component placement must be linked to a shape code in the appropriate machines, and the process is further weighed down when new components are introduced that do not already have a shape definition. Since material data are frequently difficult to find before receiving a physical unit, a final check must be made when the material has gotten to the floor. This results in delays that can extend into weeks. The engineering cost, and
amount of time spent, are part of the cost of new product introduction. If not managed properly, they will have detrimental effects on the release cycle. This can lead to profit or mar- keting losses as competitors race to bring out their own products. Another issue is the assignment
of a line configuration to just one product. The time spent in prepara- tion is then compounded by the work it takes to switch a product from one line configuration to another. Many tasks, such as extracting and enter- ing data from one system into anoth- er, have to be repeated — with the same care taken to avoid errors. The amount of qualification required to ensure that no mistakes have crept into the machine programming and optimization, the shape data confir- mation, rotation adjustment, etc., keeps the cost of moving a product between lines quite high. The practice of dedicating a product to a line can create ineffi-
ciency which is effectively built into the production cycle. For example, if a line is capable of completing 2,500 PCBs per day, it then runs at maxi- mum efficiency only when 2,500 units are required by the customer. Matching supply with demand per- fectly in this way is highly unlikely.
Current Practices Many times supply and demand
are balanced by slowing a line’s out- put. A downgrade of 10 or 20 percent might be acceptable in some situa- tions as it can be “hidden” from scrutiny, but the alternatives are
worse. Productivity is typically meas- ured by a ratio of output to target. Time lost in production planning is often not recorded and is also hidden. To change the line over and tem- porarily produce something else would require at least two product
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