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OEMs are constantly maintaining or, better put, trying to trim their manufacturing budgets while ensuring product reliability. A big area of interest in the cost-cutting process is the assembly of printed-circuit boards (PCBs).

But with their wide array of devices, components, and component types plus their various mounting processes, PCBs offer great potential for errors and big expense. One solution gaining popularity in this arena is pin-in-paste (PiP) technology.

WHAT IS PIP TECHNOLOGY?
PiP technology is a reflow soldering technique that eliminates the separate steps required for soldering surface-mount (SMT), through-hole (THT), and other types of components to a PCB. It’s also known as alternative assembly and reflow technology (AART), top-mount (TMT) reflow, THT reflow, or intrusive reflow.

For example, a basic single-board computer usually supports a variety of SMT (semiconductors, passive components, etc.) and THT components (edge-card connectors, headers, jacks, etc.). Each of these components requires a unique variation of the soldering process. Generally, the larger THT components require more solder than their SMT counterparts and therefore exhibit a stronger, more reliable connection. SMT components require less solder and a more intricate process.

PiP technology enables tandem reflow soldering of each component type within a single step, allowing the use of THT components within SMT manufacturing processes. The THT connectors may be manually or automatically positioned on a circuit board and soldered simultaneously with the SMT devices. Unique to the PiP process, the THT components retain the same mechanical strength as if soldered separately.

THE HOW AND WHAT OF PIP
How components mount to the PCB will vary depending on the application, number and types of components, board thickness and type, and several other factors. In general, there are five steps to the process (Fig. 1).

First, a stencil covers the plated PCB holes. Second and third come the application of solder paste to the stencil followed by removal of the stencil, respectively. Fourth, there’s auto or manual placement of components on the PCB. Finally, the PCB goes into the reflow oven.

To take advantage of the process, components must be compatible with PiP. Requirements dictate that the components be made of a high-temperature-resistant material with standoffs for heat evacuation and a consistent solder flow. Optimal pin lengths are in the vicinity of 0.2 to 0.4 mm and solder tails at 2.9 mm as per IEC 61076-4-104.

Other criteria include compatibility with pickup via vacuum nozzle or grippers and a design conducive to vision inspection. As an example, the Millipacs Type C headers from FCI USA feature PiP terminations (Fig. 2). The 2-mm header family includes five- and eight-row versions, all of which employ a reflow temperature-resistant resin construction.

THE PIP ADVANTAGE
The ability to eliminate steps in the manufacturing process is a major plus for reducing costs. Simply put by Bavo Teunissen, marketing communications director for FCI, “PiP technology helps to process SMD and THR components on the PCB using the same machines and procedures in a single step. It eliminates wave/selective soldering or press fitting, saving time and costs.”

There are several other advantages the technology, including more reliable and robust solder connections, which translate into a lower defect rate and higher yield compared to wave soldering. The PiP process eliminates one or more thermal processing steps as well, additionally improving solderability and component reliability.