PCBA Tech - Reflow soldering process of through-hole plug-in in PCBA processing

Friends who have a little understanding of PCBA processing and SMT chip processing know that in general, the chip components correspond to reflow soldering (Reflow Soldering) or SMT (Surface Mount Technology), while plug-in electronics The components correspond to Wave Soldering, or THT (Through Hole Technology). But today, Shenzhen Youqin Electronics will talk to you about the through-hole plug-in reflow soldering technology (PIHR: Pin-in-Hole Reflow) based on years of PCBA processing experience.

Through hole plug-in reflow soldering in English is PIHR or Pin-in-Hole Reflow, and some are called THR or Through Hole Reflow, which refers to inserting the pins with electronic components into the plug-in hole filled with solder paste and using reflow soldering The process method can realize simultaneous reflow soldering of through-hole devices and surface mount components. PIHR process is an innovation in electronic assembly. Compared with traditional processes, it has great advantages in economy and advancement. It can partially replace wave soldering, selective wave soldering, automatic welding robots and manual welding.

The advantages of through-hole plug-in reflow soldering compared with wave soldering:

The reliability is high, the welding quality is good, and the defective rate per million (DPPM) can be lower than 20.

Welding defects such as false welding and continuous tin are few, and the workload of repairing the board is reduced.

The PCB surface is clean and the appearance is obviously better than wave soldering.

Simplifies the process and reduces labor intensity. The conventional plug-in wave soldering is omitted, and through-hole plug-in reflow soldering is used instead, and there is no slag problem of wave soldering. At the same time, the reflow soldering operation is simpler than the wave soldering operation, and the labor intensity is lower.

The scope of application of using reflow soldering instead of wave soldering when SMT is mixed:

SMT mixed mounting refers to different mounting processes such as THT and SMT involved on the same side or both sides of the PCB.

Most mount SMT, a small amount of plug-in THT, especially for some through-hole connectors.

The material of the plug-in device must be able to withstand the thermal shock of reflow soldering, such as coils, connectors, screens, etc.

PIHR process requirements of through-hole plug-in reflow soldering for SMT equipment

Requirements for printing equipment: When double-sided mixing, because the components to be plug-in components have been soldered and mounted, the stencil template can not be used to print solder paste, and a special three-dimensional tubular printer or dot is required. The soldering machine applies solder paste.

Requirements for reflow soldering equipment:

During the reflow soldering of the through-hole plug-in unit, the component surface is on the top and the soldering surface is on the bottom, and the furnace temperature distribution is required to be exactly opposite to that of the patch reflow soldering. Therefore, the through-hole plug-in reflow soldering must have the entire reflow oven that can independently control the temperature up and down in each temperature zone, and can make the bottom temperature higher. Generally, hot air furnace or hot air + far infrared furnace with higher furnace temperature and uniform temperature is used. The methods available in actual operation include: adjusting the temperature curve of the existing reflow oven; using special shielding tooling for reflective material processing on the existing reflow oven; using special equipment such as "spot solder reflow oven".

The requirements of the reflow soldering process of the through-hole plug-in to the components

The requirements of the through-hole plug-in reflow soldering process for components are embodied in the components that can withstand high temperatures, and the pins of the components are formed. Specifically, the components can withstand a thermal shock greater than 230°C for 65 seconds (tin-lead process) or greater than 260°C for 65 seconds (lead-free process). The lead length of the component should be equivalent to the PCB thickness. It forms a square or U-shaped cross-section (rectangular is better).

For the through-hole plug-in reflow soldering process, the key points are the calculation of the amount of solder paste (generally estimated to be twice that of solid metal), the pad design of the through-hole components, the design of the stencil for printing solder paste, and the application of solder paste Method and so on.