LGA/QFN Floating on Reflow Print E-mail
User Rating: / 0
PoorBest 
Written by Chris Hunt   
Tuesday, 04 September 2012 02:29

 

Kill the opens through tighter stencil apertures.

Open solder joints caused by lifting of a land grid array (LGA) package during reflow are very common. This is normally very easy to overcome with good stencil design.
The most common reason for problems with these parts is excess solder paste under the center pad of the package, which causes the part to float on the surface of the solder. As a basic guide, the center pad stencil aperture should be reduced to 50% to 60% of the area of the pad. Depending on the size of the pad, the area should be split up with four, six or even nine equally spaced apertures. This modification reduces float on reflow and increases the chance of the volatile elements of the solder paste escaping, reducing void formation in the joint interfaces.

Blind via holes in the center pad can also cause lifting of the part during reflow and, where possible, vias should be plated up to reduce the impact during manufacture.

Figure 1

These are typical defects shown in the National Physical Laboratory’s interactive assembly and soldering defects database. The database (http://defectsdatabase.npl.co.uk), available to all this publication’s readers, allows engineers to search and view countless defects and solutions, or to submit defects online. To complement the defect of the month, NPL features the “Defect Video of the Month,” presented online by Bob Willis. This describes over 20 different failure modes, many with video examples of the defect occurring in real time.

Chris Hunt is with the National Physical Laboratory Industry and Innovation division (npl.co.uk); This e-mail address is being protected from spambots. You need JavaScript enabled to view it . His column appears monthly.

Last Updated on Tuesday, 04 September 2012 14:46
 

Columns

Eastern-US: China’s New Competitor?

Parity emerges among EMS Factories from Asia, Mexico and the US.

For the first time in years we see parity in the Eastern US among EMS factories from Asia, Mexico and the US. This EMS market condition will permit American OEMs (the EMS industry refers to OEMs as customers) to have more EMS pathways to choose from. Now more than ever, such EMS assignments will require deeper investigation relating to the OEMs’ evaluation of manufacturing strategies.

Read more...
 
The Human Touch

For those who count on the electronics industry for big feats, it’s been a remarkable couple of years.

Read more...
 

Features

Advances in Concentration Monitoring and Closed-Loop Control

Contaminated bath water skews refractive index results. New technology can accurately measure aqueous cleaning agent concentration.

Read more...
 
Circuits Disassembly: Materials Characterization and Failure Analysis

A systematic approach to nonconventional methods of encapsulant removal.

Read more...
 

Search

Search

Login

CB Login

Language

Language

English French German Italian Portuguese Russian Spanish
 

Products

Techspray Introduces Fine-L-Kote High Viscosity AR Conformal Coating
Fine-L-Kote high viscosity AR acrylic conformal coating reportedly widens the process window and flexibility. Can use as-is for dipping or thin down for spray systems. Is for selective spray systems...