Prototype of Pulsar Heart Rate Watch Board

Using a reflow oven (custom made), I was able to assemble the bluetooth watch board with the system on chip (SoC) part, lithium ion battery charger, LEDs, connectors, etc.  This board is the main board doing the signal processing and Bluetooth 4.0 Low Energy radio transmission of the heart rate data to a smartphone.
Watch Board
The crucial part to assembling a board with QFN package parts is the solder mask stencil.  The QFN parts are 0.5mm pitch (0.5mm from the middle of lead to another) which makes it almost impossible to solder without a reflow oven or a reflow heat gun.  I obtained the stencil from  For one sheet with 1.23″ by 1.23″ board size total cost was about $30 with shipping.  Although what you get seems like a transparency paper with some holes, it is definitely worth the time saved during assembly.
For more detail: Prototype of Pulsar Heart Rate Watch Board

About The Author

Ibrar Ayyub

I am an experienced technical writer holding a Master's degree in computer science from BZU Multan, Pakistan University. With a background spanning various industries, particularly in home automation and engineering, I have honed my skills in crafting clear and concise content. Proficient in leveraging infographics and diagrams, I strive to simplify complex concepts for readers. My strength lies in thorough research and presenting information in a structured and logical format.

Follow Us:

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top