SMT as a standard

The PCB component mounting process has progressed from Pin-in-Hole or Through-Hole-Technology (THT) to the faster and more flexible Surface Mount Technology (SMT). Today SMT is THE standard PCB assembly process.

Design from experience

Standard process parameters help in making the PCB and stencil layout design easier. Therefore Weidmüller suggests the follwing guidelines for our SL-SMT pin headers with 1.5mm long pins:

• PCB hole diameter: 1.5 mm
• Solder pad diameter: 2.3 mm
• Stencil hole diameter: 2.1 mm
  (at sufficient paste filling angle)
• Stencil hole diameter: 2.8 mm
  (at too low paste filling angle)
  

valid for
PCB thickness: 1.5 - 1.6 mm
stencil thickness: 0.12 - 0.18 mm

Disposing low volume in optimal form

Weidmüller SL-SMT pin headers short octagonal pins with chamfered pin ends contribute to keeping the required paste volume as low as possible. The small pin length of 1.5 mm for standard circuit boards of 1.6 mm thickness allows to achieve an optimum shape of the soldered joint already with a paste filling degree of approx. 90 %.

Furthermore, regular one layer stencils can usually be used for squeegee speed and squeegee pressure for fine-pitch technology and the standard process parameters.

Unbeatable advantage: During the equipping process, the paste gets less squeezed out of the equipping hole.

Short pins - high performance

By using short (1.5mm) pins, more products per Tape on Reel or Tray are possible. This is achieved on the one hand by the very low height of the SL-SMT pin header and on the other hand by the reduced packing height. The packaging is norm-compliant and anti-static, thus making fully automated PCB assembly possible via market-standard Pick & Place systems. The short pins of the SL-SMT enable the optimization of the travel-height thus removing the possibility of collisions between the components and the PCB. The short pin length and low weight of the SL-SMT pin headers also maximize the component placement precision.

The material of the future

The high temperature resistant, halogen free plastic LCP (Liquid Chrystal Polymer) has a melting point of 335° C. Because of this it shows very good thermal stability for higher soldering temperatures. The LCP pin headers are oriented to be 100% useable in every lead-free soldering process. Another decisive advantage of LCP is the extremely low coefficient of thermal expansion which is very similar to that of the PCB base material. The result is zero PCB warpage after cooling.

Better control

The objective is to enable the swift and simple assessment of the solder joint quality for long or short pin THR components via manual-visual inspection, computer-aided image evaluation or radiographic X-ray inspection. Recognized norms and standards are hereby fulfilled worldwide.
Our SL-SMT pin headers are specially designed to allow visual inspection of the primary side of the PCB, therefore fulfilling the requirement worldwide recognized norms and standards.