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 download this pdf document.
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