Assuring PCB Shelf Life Solderability by Air Levelling

Processes for protecting copper surfaces during storage for solderability purposes were evaluated. The reason for the evaluation was to select the most cost effective method of achieving long‐term shelf life. A solderability test method was selected for the programme after reviewing various qualitative techniques such as Rotary Dip, IPC‐S‐801, MIL‐S‐202 Method 208, and the automatic quantitative Meniscograph instrument. A solderability test selection method was considered critical in the programme. Tests were conducted at 3 month intervals over a period of 1 year. From the data, a relative cost comparison showed air levelling to be more economical than organic sealers or hydrosqueeze. Air levelling has shown that circuit and plated‐through‐hole solderability can be maintained for a minimum of 1 year shelf life and is a practical process for both small and large production runs. When solder thickness was assured, test results also showed that both hand soldering and wave soldering could be performed on hard and flexible circuits without measling and pad lifting. The advantages of the process are presented in the paper so that the programme benefits can be applied to both present and future printed circuit board fabrication methods, including additive techniques. Manual soldering benefits of 300% improvement in wetting time and 90% faster wave soldering speeds were possible on air levelled surfaces. The levelling process covers both copper circuit sides of double and multilayer PCBs independent of circuit complexity and ground planes. This paper was originally presented at the First Printed Circuit World Convention held at the Cafe Royal, London in June, 1978.