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BESTPROTO- Turning Your Prototypes into Products

 

Guidelines on Making Your Prototype Builds "Assembly Ready"

 

 - March-April 2007
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Included in this newsletter are guidelines that help insure the success of your next prototype build. This is the first in a series that will provide board layout tips which will lead to a more trouble free, faster turnaround prototype build .

The guidelines below can help you standardize the fabrication and assembly of your product, while lowering its cost. When followed, these help reduce errors and make sure that your prototype can be built as quickly as possible.

As always we invite you to call if we can help you build your next prototype at (847) 797-9250.

The following guidelines apply to making your SMT components "assembly ready" and should be thought through prior to the final design of your prototype assembly:

1. It is preferable to use parts that can be cleaned in an aqueous wash. This allows the assembler to use a flux which insures the greatest wetting of the solder to the pads.
2. Send BESTProto components that are "standard" sizes and values. For example, if using 100K parts, it is best to standardize the assembly with 1% tolerance components rather than use some with 1% tolerance and others with 5%. If using the same value component, it is best to standardize the assembly with one size (eg 0603) rather than use two different sizes (eg 0603 in some areas of the board and 0201 in other areas).
3. Polarity orientation during layout also has an impact on the proper manufacturing of the circuit boards. Make sure that all polarized components are oriented in the same direction. Polarities should face all left, all right, all up, or all down, if possible. It is also critical that the polarity markings are available in the CAD information. Land patterns for components that can be electrically connected only one way must have some way of designating polarity. It is important that the polarity marking on each component be visible even after the component is mounted to aid inspection.

The following list indicates the typical "best practice" ways to designate polarity on your PCB for certain components.

Through-hole DIPs . Through-hole DIPs should have a "1" or a dot in the silk screen next to Pin 1. All pads of the DIP should be round except for the pad of Pin 1, which should be square.

Through-hole connectors Through-hole connectors should have a "1" in the silk screen pattern next to Pin 1. All pads of the connector should be round except for the pad of Pin 1, which should be square. For connectors with more than one row, Pin 2 or the last pin of the connector should be designated as to how the pins are numbered.

Through-hole polarized capacitors Through-hole capacitors should have a "+" in silk screen next to the positive pin's pad. The positive pin's pad should be square while the negative pin's pad should be round.