PCB manufacturing- through-hole-reflow (THR) proces

Using a through-hole-reflow (THR) process can save money during assembly and enables a more compact placement of components. On my iMX8 PCB I´m using a THR process for the HDMI, USB-C and Industrial Ethernet connector. In this process the through hole pads are filled with solder paste during the stencil printing.
Before placing the components on the board a heat curing glue is applied to the PCB to secure the parts in place during the second reflow cycle. The boards are reflowed with a standard profile which solders the TH pins to the PCB.
The advantage of this process is that no manual, selective or wave soldering is required. Another benefit is that no solder bump is generated on the opposite side of the PCB if the pins of the THT components aren´t longer than the PCB thickness. This makes it possible to utilize that space for other connectors. I´ve done so on my iMX8 board. The SD card connector hast a standoff height of 0.1mm with a plastic insulated bottom side. Under these circumstances it is possible to use the space on the opposite side of the PCB where a THT component is placed.
There are also some drawbacks in this case. An additional step of applying SMD glue is needed. Also optical inspection of the solder joint is only possible in mid-process when only the side containing the THT connectors is populated.

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