Original Date: 08/20/2001
Revision Date: 12/14/2006
Best Practice : Pin in Paste Dual Technology
Pin in Paste Dual Technology is an efficient method for manufacturing circuit card assemblies that require both through-hole and surface mounted components. This single assembly-line process is very consistent once the specific parameters are established and tuned for the equipment used.
In the past, the method for manufacturing circuit card assemblies (CCAs) that required both through-hole and surface mount components was time consuming and labor intensive. The assemblies were subjected to screen printing of their printed circuit boards (PCBs); placing and reflowing of the surface mount components; manually inserting the through-hole components; masking; and wave soldering. During wave soldering, an opportunity existed for temperature shock (stress) to be introduced into the process. In addition, the solder flux used required CCAs to immediately undergo a water wash step for cleaning. Inspections for workmanship defects and rework occurred after each component population step. In cases of double-sided circuit boards, the procedure incorporated repetitive loops for component population. When two different process lines were in operation, the repetitive loops created disruptions and delays for work in process. In 1998, Lockheed Martin Naval Electronics & Surveillance Systems- Surface Systems (NE&SS-SS) redesigned its process so that CCAs, requiring through-hole and surface mount components, could be manufactured on a single assembly line.
The Pin in Paste Dual Technology is compatible with single-sided CCAs using PCBs up to 0.120-inch in thickness, as well as double-sided CCAs using PCBs up to 0.100-inch in thickness. PCBs are now printed via an automated solder paste printer capable of multiple sweeps. CCAs are processed using a convection reflow oven in a nitrogen environment with an approximately 2°C/second temperature ramp rate. Multiple paste screens enable the Pin in Paste Dual Technology to be an efficient method for assembling CCAs requiring both through-hole and surface mounted components on the same assembly line. X-ray inspection is utilized to identify any internal voids. The assemblies meet the requirements of IPC J-STD-001.
A two-step printing may be required if CCAs require both through-hole and surface mounted components to be on the same side of the board. The printing would consist of one thickness of screen to print paste the surface mount components, and then a thicker screen to print paste where the through-hole pin connector is mounted. The process of milling the underside of the thicker screen, to avoid contact with the surface mount paste of the first print, protects the original paste while the thicker paste is printed at the connector holes.
The Pin in Paste Dual Technology utilizes many elements (e.g., no-clean flux, solder paste) which help reduce the process cycle time. The specialized screen printing mask allows non-wash processing of many PCBs, which eliminates the wave soldering and washing steps. The gradual heating of CCAs through the convection solder reflow ovens decreases the possibility of introducing temperature shock. The single assembly line approach streamlines the manufacturing process and makes test failures easier to locate, thereby increasing feedback and reducing rework. Since implementing the Pin in Paste Dual Technology, Lockheed Martin NE&SS-SS reduced its cycle time by 40%.
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