CUSTOMER ISSUE: The Helpline received a call from a customer who had a question about their electronics manufacturing process of a circuit board. Their process was currently using 0805 size discrete passive components, and with the rapid evolution of electronics manufacturing, they were switching to 0603 components. Their question was how close can the new spacing be? And were there any other concerns to consider? Their current spacing of component placement was determined to be at 0.050" spacing on the 0805.

The helpline fielded this customer's question following is the summary of the Helpline response. Component placement machines generally are capable of +/-2 mil accuracy (if not better), and therefore could easily place components as close as they would like. The machines could even place the components on top of one another if desired.

The only concerns that dictate any spacing at all are for the inspection and repair/rework of the components once the assembly is built. Abuffer zone around a component might be needed because the adjacent part might be unusually high, and the closest solder joints may be hidden from view if the components are placed too close together. A buffer zone may also be required for the insertion of a soldering/desoldering tool, and for the heating/reheating needed to perform a repair. In effect then, the proximity of other components should also be considered as well as the component type itself.

Concerning 0603s to another discrete component, the spacing from pad to pad, metal to metal, based on average rework and repair capabilities should be approximately 0.015". The spacing from a 0603 component or any other chip discrete component to another surface mount part depends on the space needed for inspection, rework or repair, and that also will vary with the inspection and repair capabilities of a given factory. Approximate numbers might be 0.030" to a normal surface mount part (TSSOP or TQFP), or 0.050" to a high surface mount part (QFP, LCCC). If the next nearest component is a large connector, however, 0.100 inches or more of spacing may become necessary in order to ensure enough space for the local heating needed for a rework or repair of such a large component without damaging adjacent components. The fact of the matter is that the currently existing 0805 components could be spaced just as closely as the upcoming 0603s, if inspection and repair capabilities are sufficient.

The customer was informed that there are some approximate guidelines and no hard and fast rules, and that the Helpline could make some suggestions based on normal rework capability. The customer agreed that the final analysis must be performed in his particular shop with the specific rework/repair personnel and equipment that will be used on the assembly in full production.