CT3680 V1 Connector Manual Soldering Hints

The CT3680 V1 edge connector is 40 pins (20 per side), 0.8mm pitch (pin spacing). We recommend using the Samtec HSEC8-120-01-S-DV-A surface mount connector which is available on our website, and at many electronics suppliers.

A custom footprint file is also available for PCB layout that includes a silk layer outline of the CT3680 module (to help avoid mechanical conflicts with nearby components) and extended pads to help with manual soldering of the connector.

With careful preparation this connector can be manually soldered using solder paste and a fine tip soldering iron. The connector pins project a small distance out from under the recessed edge of the connector body, enough to achieve reliable manual soldering:

The extra long pads of the custom footprint (used on our development board and DIL adapter board) help bring the pads out from under the connector for better manual soldering access.

Everyone tends to have their own way of doing SMT manual soldering. We have used the following procedure with good results:

1. Apply a small amount of quality soldering paste to each pad. Do not use too much as any solder bridges will be quite difficult to remove since a lot of the pad and pin are under the body of the connector. Remove as much paste as possible from between the pads. If you are building your own custom PCBs it is very worthwhile to get stencil made for the solder paste. A stereo microscope is very helpful in this process.
2. Place the connector on the PCB, the alignment pins will ensure exact placement and correct orientation.
3. Clamp the connector in place while soldering to ensure each pin is firmly on its pad. We find that a rubber band wrapped around the board and over the connector works well as a clamp.
4. Using a small chisel shaped soldering tip, slide the hot tip from the ends of the pads to under the recessed edge of the connector and against the tip of the pins (which project out just slightly from under the edge of the connector). Hold it there for a few seconds to melt the solder paste and heat the connector pin enough to make a good solder connection. Then drag the tip out and off the ends of the pads (this helps pull the solder along the pads and avoid bridging). It may be helpful to position the board at an angle to get a view under the recessed edge of the connector while soldering.
5. Repeat this down the line of pads on both sides. Do not drag from pad-to-pad, drag only from the outside edge, into the pins, and back straight back out to the edge again.
6. Carefully examine the solder joints under a microscope making sure each pin is embedded in the solder and there are no bridges.
7. Using a fine pick tool, remove any stray solder balls or remaining paste from between and around the pads.
8. Test continuity of each pin from the PCB to the inside of the connector and ensure no pins are open or shorted together.