BOTTOM TERMINATED COMPONENTS – the challenges and solutions
This paper explores the challenges of reflowing Bottom Terminated Components – referred to as BTC and including QFNs (quad flat no leads), LGAs (land grid arrays), DFNs (dual flat no leads), MLF (micro lead-frame) The main issues discussed are Coefficient of Thermal Expansion (CTE), flux entrapment, voiding and explains the innovative solutions that Retronix offer for these issues.
Problem : Coefficients of Thermal Expansion affects high reliability and harsh environment electronics in particular. When you have two materials of a different thermal expansion rate you can find the stress that this causes between the two materials can lead to fractures and cracks.
Retronix Solution : What Retronix can offer is the addition of solder balls/bumps to the pads of BTC part meaning that the component will be placed with an increased solder mass and better thermal conductivity between the component and the PCB.
Problem : Flux Entrapment under BTC parts is an increased risk compared with devices that are elevated (however minimally) from the PCB.
Retronix Solution : The elevated final location from the ball attachment ensures a clearer pathway to allow your cleaning process to tackle the flux residue and rather than entrap it, ensure it flows through and is removed from the PCB.
Problem : Voiding, like flux entrapment is also a direct effect of poor outgassing channels.
Retronix Solution : Creation of more defined channels for flux outgassing during reflow has been proven to offer a very effective solution for excess voiding.
For a more detailed explanation please feel free to download this pdf document.
Click here to connect with Rob
Click here to follow the Retronix LinkedIn Page
Click Here to follow us on Twitter
Click Here to see our process videos on YouTube.