Best PCB guidelines for SMT Assembly Machine.

In this tutorial, we are going to learn about the Best PCB guidelines for SMT Assembly Machine.

Component Placement and Spacing in PCB Layout Design

Try to avoid the components being placed in random orientation.

Place the through-hole components should be on one side and SMD components should be on another side.

When placing the through components then Hole to hole spacing for most important components (end-end, side-end and end-side) should be 2.54 mm or more if required by body size and also a hole to hole spacing between socket & another component should be 4 mm or more.

Always place the edges of the board clear from pads, holes, traces & components for at least 1mm.

Placement Component Lead Spacing and Hole Sizes should be as per below

  • Radial component lead spacing should be 5.08 mm and it is not recommended to use a 2.54mm span.
  • Axial component lead spacing should be 8mm to 20mm with max. Body size 7mm D x 17 mm L

Here is the recommendation to use the following span for widely used components

  • 1/4w resistor and diode: 12.7mm
  • Bypass axial cap and small axial cap: 9.525 (fits all axial equipment.
  • Small axial type die. cap: 18mm to 20 mm with body less than 12.7 mm L 7.62 mm Min. distance from center of hole to end of body: 0.07″ to 0.120″ depends on lead size, for 1.5 mm.
  • For leads, we recommend a min. distance of 2mm and Min. hole size should be Lead diameter + .254 mm + Tol 1.54mm.
  • For through hole components, it is recommend the following hole size for widely used components: a) 1/4w resistor and small caps: 1.016mm, while  0.96mm  should be the absolute min. (b) IC pins and similar pin size: 1mm, while .9mm should be the absolute min. c) IC socket pins: 1.106mm, while 1.0mm should be the absolute min.

How to Selection of Components

  • Try to Use axial components instead of radial components.
  • Use machine insertable components instead of manual insert components.
  • Use same technology components instead of mixing technology components (SMD and through holes).

PCB Layout Consideration

  • For SMD layout, place 3 pads (1.016mm and up) as fiducial marks (free of mask) at approximately 12.7mm from the corner of the PCB panel. If the PCB panel has more than one unit, do the same for all subpanels.
  • For SMD with fine pitch components (less than 0.9mm), place 1 pad (1.016mm & up) as local fiducial mark at the center location of that components.
  • For through hole components, keep pad size 0.3556mm lager than hole sizes.
  • For BGA devices, don’t place via at the pads, unless blinded vias are used at a higher board cost.

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