This paper will focus on the application requirements of solder printing small aperture designs, concentrating on 008004 (inch) / 0201 (metric) size components, and the results of a design of experiment printing these challenging apertures. As Moore’s law continues to be applied to component miniaturization, the next installment of reduced packaging has arrived in the form of the 008004/0201 for resistors and capacitors.
MPM Printers Technical Papers
In simplest terms, a faster printer logically means higher throughput. Overall speed, however, is dependent upon a number of factors including the individual cycle times for various steps in the print cycle (e.g., stencil wiping frequency, board separation and printing speed).
Process traceability and verification has become increasingly important as electronics assembly has moved to higher throughputs and volume requirements with tighter process windows.
Stencil printing today requires a higher degree of printer accuracy than ever before. Printer accuracy becomes increasingly difficult to maintain as demands for higher speeds and throughput test the limits of a printer’s capabilities, particularly with tiny apertures and tight land patterns.
Paste-in-Hole (PIH) printing, a.k.a. through-hole printing, pin-in-paste, intrusive reflow, etc., has always been a way to accommodate traditional through-hole components on a mixed-technology SMT assembly using reflow soldering rather than wave to make the through-hole connections. Paste is printed in such a manner to as to fill the through-holes, the through-hole components are inserted, and the assembly is reflowed.
Fine pitch/fine feature solder paste printing in PCB assembly has become increasingly difficult as board geometries have become ever more compact. The printing process itself, traditionally the source of 70% of all assembly defects, finds its process window narrowing.
Stencil printing technology has come a long way since the early 80’s when SMT process gained importance in the electronics packaging industry. In those early days, components were fairly large, making the board design and printing process relatively simple. The current trend in product miniaturization has led to smaller and more complex board designs.
Stencil printing is a critical first step in surface mount assembly. It is often cited that the solder paste printing operation causes about 50%-80% of the defects found in the assembly of PCBs. Printing is widely recognized as a complex process whose optimal performance depends on the adjustment of a substantial number of parameters.
The techniques described have proven to be robust and particularly well suited for detecting troublesome bridge and bridge-like features that span the gap between pads.
Increasingly fine pitch component patterns on PCBs, and ever-smaller passive components such as 03015’s continue to narrow the process window for PCB assemblers.