Connectors are almost always a driving cost in electronics designs, and my board is no exception. In terms of the bill of materials (BoM), the connectors are responsible for half the cost. For this reason, I spent more time looking for a good deal on the connectors than on any other item on the BoM.
First, I wanted to make sure I had selected a good connector. I knew I wanted to be able to chain up multiple digits, but I also wanted a smooth edge on the outside. Additionally, I wanted the ability to rotate any digit in the chain by 180 degrees and still be able to link digits together. That specification required a connector that did not hang over the edge. I decided to go with a female connector for both input and output connectors and to use long-tailed, unshrouded male header pins as the interconnect. A 0.100-inch pitch would make my selection compatible with many existing connectors and prototyping systems, which would be valuable for any hobbyists that buy the product. A surface mount option would make the board easy to assemble.
With specs in mind, I needed to see if the connector I wanted existed and what options were available. My go-to source for connectors is Samtec. In my experience, they are the definitive source for connectors. Their website is relatively easy to browse, with a huge selection and great documentation. Their major advantage is that they will ship overnight samples of anything you want for free. I started browsing in the .100-inch pitch connector section and found the SSM series. This connector comes with a right angle, surface mount option. It also mates with the TSW series, which can include a long tail for the interconnect.
Samtec's connectors are excellent quality, but they are expensive. In small quantities, each connector was $1.22, and I needed four per board. For small runs, it's very convenient to avoid worrying about sourcing connectors. For this product, I needed something cheaper, or the final product would be too expensive to sell at retail. Because the price breaks at Samtec did little to improve the cost, I had to look elsewhere. Unfortunately, distributors like Digikey and Mouser weren't much help. I even used my early access at parts.io, but there were not many options. Finally, I resorted to Google. I searched for "surface mount header" and clicked on any link that looked like the product. There were a few manufacturers and distributors listed. Sometimes distributors have links to datasheets, which I can use to find new manufacturers to look at. Some of the manufacturers required me to fill out a form to request a quote by email. After a few of them got back to me, I had a new, lower price and a much higher minimum order quantity (MOQ): $0.55 each with a MOQ of 2,700 connectors.
The minimum quantity of connectors will drive the minimum quantity of boards I can make cost effectively. The price of the connectors will also have a large effect on the price of the completed board. I'll discuss more details about costs and pricing in future posts.