-
- News
- Books
Featured Books
- smt007 Magazine
Latest Issues
Current IssueComing to Terms With AI
In this issue, we examine the profound effect artificial intelligence and machine learning are having on manufacturing and business processes. We follow technology, innovation, and money as automation becomes the new key indicator of growth in our industry.
Box Build
One trend is to add box build and final assembly to your product offering. In this issue, we explore the opportunities and risks of adding system assembly to your service portfolio.
IPC APEX EXPO 2024 Pre-show
This month’s issue devotes its pages to a comprehensive preview of the IPC APEX EXPO 2024 event. Whether your role is technical or business, if you're new-to-the-industry or seasoned veteran, you'll find value throughout this program.
- Articles
- Columns
Search Console
- Links
- Events
||| MENU - smt007 Magazine
Bumping of QFNs/LGAs and Other Leadless Devices for More Consistent Rework
August 9, 2016 | Bob Wettermann, BEST Inc.Estimated reading time: 2 minutes
The Challenge
Leadless devices are now the greatest package style by volume (Yole Development Market Survey) being placed by electronics assemblers worldwide. These packages, due to a variety of factors, are challenging to rework. Among the greatest challenges this package presents are the solder voiding primarily on the ground plane, the inability to clean underneath the devices post rework, and the difficulty in getting similar standoff heights on both the IO and center ground. These challenges along with their increasing complexity and ever smaller package sizes challenge even the most skilled rework technicians.
In addition to the above rework challenges, the package style itself remains very difficult to inspect post reflow for a variety of reasons. As there are rarely any visible solder joints due to in most instances a lack of a solderable sidewall on the IO pads of the device, as well as the very low standoff distances between the bottom of the device and the PCB, there is very little visual inspection which can occur. This means that the reliance on a skilled x-ray technician as well as a capable x-ray system is in order.
Types of Rework Methods Available
Of the various methods for reworking leadless devices, the bumping method (Figure 1), when appropriate for the board and part at hand, is the process with the greatest first pass yield, the one with the greatest standoff distance for cleaning flux residue from underneath the device and the one with the greatest assurance of minimizing voiding.
Figure 1: Bumped leadless device prior to placement.
"Bumped" 2 x 2mm QFN Package, 0.5mm pitch, 0.2mm Wide Pads
There are numerous methods being used to rework leadless devices; either guided by the older IPC 7711 5.4.1 process guidelines or by the newest stenciling techniques. The older of these methods includes solder paste printing on the site location of the PCB followed by the placement and reflow of the device. The newer methods including IPC 7711 procedures 5.8.1.1 and 5.8.1.2 includes the device pads being “bumped” followed by their placement. The device, post “bumping”, can be placed using a rework system using paste flux or with a properly-designed “capture” stencil which has apertures that can locate and capture the “bumps” on the PCB.
Both of these latter methods for reworking leadless devices were popularized using polyimide stencils. In these methods, a polyimide stencil is placed over the land patterns on the bottom of the device. Solder paste is then squeegeed in to the apertures. The device is then reflowed. Post reflow, the stencil is peeled off leaving “bumps” on the bottom of the device (mini metal stencils can also be used when appropriate). Because the reflow is done in air, the flux volatiles can escape, thereby having the “bumped” part nearly free of voids. In addition, these stencils are thicker than the initial manufacturing stencils meaning that the final standoff height is greater when compared to traditional printing and placement. This bumping technique also greatly simplifies placement of the leadless device as a lower-skilled technician or even first-timer, when following the instructions properly, can produce the “bumps” for placement.
To read this entire article, which appeared in the August 2016 issue of SMT Magazine, click here.
Suggested Items
Indium Corporation Expert to Present on Pb-Free Solder for Die-Attach in Discrete Power Applications
04/30/2024 | Indium CorporationIndium Corporation Product Manager – Semiconductor Dean Payne will present at the Advanced Packaging for Power Electronics conference, hosted by IMAPS, held May 8-9 in Woburn, Massachusetts, USA.
Taiyo Circuit Automation Installs New DP3500 into Fuba Printed Circuits, Tunisia
04/25/2024 | Taiyo Circuit AutomationTaiyo Circuit Automation is proud to be partnered with Fuba Printed Circuits, Tunisia part of the OneTech Group of companies, a leading printed circuit board manufacturer based out of Bizerte, Tunisia, on their first installation of Taiyo Circuit Automation DP3500 coater.
Vicor Power Orders Hentec Industries/RPS Automation Pulsar Solderability Testing System
04/24/2024 | Hentec Industries/RPS AutomationHentec Industries/RPS Automation, a leading manufacturer of selective soldering, lead tinning and solderability test equipment, is pleased to announce that Vicor Power has finalized the purchase of a Pulsar solderability testing system.
AIM Solder’s Dillon Zhu to Present on Ultraminiature Soldering at SMTA China East
04/22/2024 | AIMAIM Solder, a leading global manufacturer of solder assembly materials for the electronics industry, is pleased to announce that Dillon Zhu will present on the topic: Ultraminiature Soldering: Techniques, Technologies, and Standards at SMTA China East. This event is being held at the Shanghai World Expo Exhibition & Convention Center from April 24-25.
AIM to Highlight NC259FPA Ultrafine No Clean Solder Paste at SMTA Wisconsin Expo & Tech Forum
04/18/2024 | AIMAIM Solder, a leading global manufacturer of solder assembly materials for the electronics industry, is pleased to announce its participation in the upcoming SMTA Wisconsin Expo & Tech Forum taking place on May 7 at the Four Points by Sheraton | Milwaukee Airport, in Milwaukee, Wisconsin.