Design Key Points of PCB Pad Dimensions

2025-03-02

Design Key Points of PCB Pad Dimensions for PIP (Pin in Paste) Process of SMT Through-Hole (PTH) Components

Pad Dimension Design for PIP (Pin in Paste) Components

1. PCB Layout Considerations

To simplify and improve the printed circuit soldering process, the Pin-in-Paste technology has been specifically developed. It replaces the original Dipping process for through-hole connectors with the SMT process of printing solder paste and then passing through a reflow oven. All through-hole components must be designed on the same side to avoid inteRFering with solder paste printing.
(1) Principle of the Ratio (PH) between Component Lead Diameter and Through-Hole Diameter:

A PH value of 0.6 - 0.8 is preferred; a PH value of 0.4 - 0.5 is acceptable; a PH value less than 0.4 is poor.
PH=Maximum Cross-Sectional Diameter of Component Lead/Maximum Cross-Sectional Diameter of Through-Hole|=φP/φH

(2) Classification of Component Lead Cross-Section Shapes: Circular, Square, or Rectangular

Circular through-holes are suitable for circular and square component leads, and the dimensions must meet the requirement: 0.36 ≤ A(P)÷A(H) ≤ 0.5.
Oval through-holes are suitable for rectangular component leads, and the dimensions must meet the requirement: L2:W2 ≥ 1.5:1.
A(P) = Maximum Cross-Sectional Area of Component Lead; A(H) = Maximum Cross-Sectional Area of Through-Hole
L2 ≈ L1 + 0.4 mm; W2 ≈ W1 + 0.4 mm

(3) Solder Paste Printing Restricted Area: The area of the component text box is the solder paste printing restricted area.

There should be no test points within the restricted area.
If there are via holes within the restricted area, they must be covered with green paint.
There should be no exposed copper foil within the restricted area (it must be covered with green paint).

(4) If the annular pad of any PTH hole is connected to the adjacent Connector pad, add at least 20 mils wide solder mask to separate them.

(5) To be suitable for the Pin in Paste process, a distance of 2.5 mm needs to be reserved between the through-hole and the pad.

2. Board Lock Design

(1) Board Lock / Kink Part:
(i) The layout should be designed with board lock / kink, and it is still mainly oval.
(ii) The dimensions of the oval should meet the ratio: L:W > 1.5:1.
(iii) The size of the oval hole should ensure that the force required to insert the component into the PCB is no more than 2.5 kg. The inserted components on the PCB should not be tilted, toppled, or prone to loosening.
(2) Boss / Guide Pin Part:
(i) The layout should be designed with boss / guide pin.
(ii) The hole diameter size should ensure that the force required to insert the component into the PCB is no more than 2.5 kg.