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November 11, 2009

Component Clearance Specification

Is there a general minimum spacing requirement we should apply to SMD components to comply with the majority of SMT pick and place systems on the market?

Are there different minimum spacing requirements for small chip caps such as 0204s and 0805s vs larger components such as QFP's?

P. R.

Experts Comments

Realistically the smallest spacing between components will be about 0.15mm. Even though a machine might be rated to place better there are several other variables that must be overcome.

First is the land pattern, if the land matches the component one-to-one its not a big variable, but ifthe land isbigger or smaller than the component it can create variation in positioning during reflow.

Next is part deviation, the tolerance of the component itselfcan be as much as 0.03mm part-to-part from the same vendor, different vendors increase the variable even more. You will also have to take into account pre-placed components, nozzle dimensional deviation and part center to nozzle deviation.

If you add it all up, 0.15mm works good. To answer the second part of the question, the minimum tolerance doesn't really change with the part size, the variables all remain about the same.

Scott Wischoffer
Marketing Manager
Fuji America Corporation
Scott Wischoffer has been in the SMT industry since 1986 with experience in service, training, sales & applications, and marketing.
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