Research
Stencil Printing Yield Improvements
Overcome Nodules and Scratches on Wire Bondable Plating on PCBs
Solder Paste Selection for Bottom Termination Components Attach
Jetting Solder Paste Opens Up New Possibilities
Advances Autonomous Driving V2X Technologies
Surface Insulation Resistance of No-Clean Flux Residues
Jetting Conductive Adhesives with Silver Coated Polymer Particles
Residues on Probing PCBAS-Consistent Connections Across No-Clean Fluxes
MORE RESEARCH
Latest Industry News
The Exodus Of Chinese Manufacturing
Autonomous Vehicles in China
How Much Gold Is in Your Computer and How Efficient It Is to Reclaim It
All must come aboard for a smooth ride to a carbon-neutral future
Memory Technologies Confront Edge AI's Diverse Challenges
How to Make Big Decisions When Facing an Unpredictable Future
Gartner Says Worldwide Robotic Process Automation Software Revenue to Reach Nearly $2 Billion in 2021
China rolls out fresh policies to boost hydrogen vehicle sales
MORE INDUSTRY NEWS

The Impact of VIA and Pad Design on QFN Assembly



The Impact of VIA and Pad Design on QFN Assembly
This paper discusses the impact of the via size and design on QFN voiding and solder protrusion. Do small vias prevent the solder from flowing onto the other side?
Analysis Lab

DOWNLOAD

Authored By:


Jennifer Nguyen, David Geiger and Anwar Mohammed
Flex
Milpitas, CA, USA

Summary


Quad Flat No-Lead (QFN) packages has become very popular in the industry and are widely used in many products. These packages have different size and pin counts, but they have a common feature: thermal pad at the bottom of device. The thermal pad of the leadless QFN provides efficient heat dissipation from the component to PCB. In many cases, arrays of the thermal via under the component is used to dissipate heat from the device. However, thermal vias can create more voids or result in solder protrusion onto the secondary side.

This paper discusses our study on the impact of the via size and the via design on QFN voiding and solder protrusion. Do small vias prevent the solder from flowing onto the other side? How should via be designed? Which via type will have less voiding issue? A comprehensive experiment was designed in trying to answer these questions. Different QFN types, via design, via sizes, via pitches and stencil design were studied using three different board thicknesses: 1.6mm, 2.4mm and 3.2 mil thick.

Conclusions


Solder was seen flowing into the PTH via with no solder mask ring during reflow process regardless of the via sizes. The smallest via size was 0.20mm (8 mil) from the study. Smaller via didn't result in less solder protrusion on the secondary side. However, less solder protrusion was seen with larger via. Via size of 0.51mm (20mil) with no solder mask ring could result in no solder protrusion, depending on the process condition. Board thickness had no significant impact on the voiding and solder protrusion. Voiding depended more on the component type and design. Solder mask ring would help to prevent solder flowing down the via at the thermal pad. The solder mask ring results some unsoldered area under the QFN component, which looks like more voiding at the QFN thermal pad.

Initially Published in the SMTA Proceedings

Comments

No comments have been submitted to date.

Submit A Comment


Comments are reviewed prior to posting. You must include your full name to have your comments posted. We will not post your email address.

Your Name


Your Company
Your E-mail


Your Country
Your Comments



Board Talk
Solder Pallets With Titanium Inserts - Yes/No?
What Rate is World Class for SMT Machines?
Selective Solder Pot Temperatures
Top Side Reflow Causing Solder Balls
Trends for Printing Ultra Miniature Chips
Should We Measure Solder Paste Thickness?
Cleaning R.F. Circuits - Aqueous or Vapor?
Why Should We Consider Smart Feeders?
MORE BOARD TALK
Ask the Experts
BGA reballing question
Conformal Coating Press Fit Connectors
Dust contamination after selective soldering
Moisture Sensitivity Level for Bare Boards
Contamination Using Solvent Dispensers
Challenges Placing RF Shields During SMT Assembly
Seeking Advise for a Solder Reflow Recipe
Critical Part Fixture During Reflow
MORE ASK THE EXPERTS