PCB Fabrication quote PCB Assembly quote Free passive parts
 

Stencil aperture considerations for QFN chips

Stencil aperture considerations for QFN chips
Quad-flat no-leads (QFN), a type of Flat no-leads package, is a surface-mount technology that connects ICs to the surface of PCBs. They have become more popular because of their near chip scale size. Designers can shrink PCB board sizes significantly because QFNs support small form factor and high density packaging and interconnection specifications.

Flat no-leads packages – QFP and others
Flat no-leads packages, such as a dual-flat no-leads (DFN), micro leadframe (MLF) and small-outline no leads (SON), are similar in package size to a QFN, but these ICs have exposed thermal pads in their center area. During reflow assembly, these ICs sometimes float on a pool of molten solder located under their thermal pads, which can prevent their terminals from being in contact with the PCB.

Reflow assembly -- when the board temperature is above the solder’s melting point, the solder paste will liquidate and form a dome-like solder drop due to liquid tension.

solder paste
A larger amount of solder paste will cover a larger area than a smaller amount. As a result, the larger area of solder paste will create a higher dome than a smaller area due to liquid tension.

higher dome
The floating solder will lift the ICs. This condition can potentially prevent contact between the ICs' terminals and the PCB pads.

excess solder
Without any paste volume control during the reflow process, one side of an IC may connect to the PCB pads while the other side may have poor contact due to the excess solder in the center of the thermal pads.
Stencil aperture size must be considered in order to control the solder paste volume in the center of the thermal pads.


« Older posts

 
Bittele Electronics Completes New PCB Assembly Line
Bittele strategy climbs turnkey PCB assembly ladder
Bittele Electronics Announces ISO 9001:2008 Certification
Bittele Electronics Reduces Customer Costs with Free Passive Parts Service
 
Design for Manufacturability (DFM) guide
Sample Bill of Materials (BOM)
Sample Assembly drawings
PCB Fabrication Specifications
 
testimonials
 
payment types
 
 
 
About Us | Services | Quality | Blog | Privacy | Contact
Copyright 2003-2017, Bittele Electronics Inc. All Rights Reserved.