-
- News
- Books
Featured Books
- smt007 Magazine
Latest Issues
Current IssueBox 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.
Boost Your Sales
Every part of your business can be evaluated as a process, including your sales funnel. Optimizing your selling process requires a coordinated effort between marketing and sales. In this issue, industry experts in marketing and sales offer their best advice on how to boost your sales efforts.
- Articles
- Columns
Search Console
- Links
- Events
||| MENU - smt007 Magazine
Novel Approach to Void Reduction Using Microflux Coated Solder Preforms
July 26, 2018 | By A. Lifton, P. Salerno, J. Sidone and O. Khaselev, Alpha Assembly SolutionsEstimated reading time: 8 minutes
Figure 5: Solder paste print design for QFN.
Components and solder preforms were placed from tape and reel using a production component placement machine with twin-head and 2N force. Samples were then inspected for skew prior to reflow in a production belt driven reflow oven per the reflow profiles defined in Figure 3. Finally, upon reflow, every component was subjected to X-ray voiding analysis capturing its largest single void size and total void percent under the thermal pad.
Results and Discussion
Voiding analysis was performed on all test assemblies. Statistical software was used to compare voiding performance and processing factors to generate a main effect plot to understand QFN voiding. The plot of the main effects on the voiding of the built assemblies are shown in Figure 6. Reviewing data, it was observed that no significant difference was observed between the two surface finishes (ImmSn and ImmAg) evaluated in this study. A very small effect of the reflow profile type was observed when all data was analyzed.
Figure 6: The main effects on voiding (%) – overall plot.
As expected, the lower voiding percentage was achieved with a high soak reflow profile compare to the straight ramp. Typically, higher soak profile allows more outgassing of volatiles during reflow, which could result in lower voiding. Reflow in nitrogen atmosphere resulted in lower voiding. Higher voiding levels were observed on the larger QFN component with thermal pad 5.4 x 5.4 mm. The results for the small and medium sized LCS and QFN packages were similar even though components’ thermal pads were very different (3.6 x 3.6 mm and 2.1 x 2.1 mm). Assemblies without vias and with through hole vias produced the least amount of voiding overall; whereas, plugged vias showed higher voiding level. The biggest effect contributing to the reduction in voiding was the use of the solder paste and preform (PF+paste) configuration versus solder paste only (SPO) configuration.
The solder paste only configuration was used as a benchmarking factor for the remainder of the analysis. The average voiding for the contributing factors for SPO configuration shown in Figure 7. The resultant voiding was approximately in 22% average range. ImmSn board finish and the high soak profile marginally drove to lesser voiding. Reflow atmosphere had very little impact on the voiding results overall. Unplugged vias were the most problematic of the three vias design in this study.
Figure 7: The main effects for SPO configuration.
Focusing on the results for PF+paste configuration only, an average voiding of 9% was measured. The overall average voiding for PF+paste configuration was more than two times lower relative to the SPO configuration. Figure 8 shows the main effect of various parameters on the voiding of the PF+Paste configuration. Unlike the SPO configuration, the primary contributor to voiding in the PF+Paste configuration was the reflow atmosphere. Reflow in nitrogen reduces voiding nearly to 5%. Clear correlation with component size and voiding performance was observed. Voiding levels of about 12% were observed on the larger QFN component with thermal pad 5.4 x 5.4 mm. Reduction in the size of the thermal pad down to 3.6 x 3.6 mm reduced voiding level down to around 9%. As expected, the smallest package with the thermal pad of 2.1 x 2.1 mm showed the lowest voiding level and it was about 5%. Like SPO configuration, assemblies with unplugged vias were the most problematic and produced higher voiding levels compared to another pad design.
Earlier conducted studies were undertaken to understand the effects of micro-flux coated solder preforms and voiding for bottom termination components (BTC). In the last several years a lot of advancement was achieved in flux chemistry development to improve voiding performance significantly. In the previous voiding studies it was identified that the higher preform-to-paste volume ratio on the pad contributed to lower voiding, specifically in nitrogen. It is evident that the increased solder volume from the preforms plays a critical role in void reduction.
To read the full version of this article, which was published in the June 2018 issue of SMT007 Magazine, click here.
Visit I-007eBooks to download your copies of Alpha micro eBook today:
The Printed Circuit Assembler’s Guide to… Low-Temperature Soldering
Suggested Items
Real Time with… IPC APEX EXPO 2024: My Role as a Technology Solutions Director
05/02/2024 | Real Time with...IPC APEX EXPOPeter Tranitz, senior director of technology solutions at IPC, shares insights into his role as the design initiative lead. He details his advocacy work, industry support, and the responsibilities of the design initiative committee. The conversation also covers the revamping of standards, the IPC Design Competition, and the implementation of design rules in software tools.
HQ NextPCB of HQ Electronics Debut on the International Stage for Electronics Manufacture at IPC APEX 2024
05/01/2024 | PRNewswireHQ NextPCB of HQ Electronics, a leading Chinese-based multilayer PCB manufacturer and assembly house showcased its industrial prowess on the international stage for the first time at the IPC APEX Expo 2024.
IPC's Vision for Empowering PCB Design Engineers
04/30/2024 | Robert Erickson, IPCAs architects of innovation, printed circuit board designers are tasked with translating increasingly complex concepts into tangible designs that power our modern world. IPC provides the necessary community, standards framework, and education to prepare these pioneers as they explore the boundaries of what’s possible, equipping engineers with the knowledge, skills, and resources required to thrive in an increasingly dynamic field.
North American EMS Industry Down 4% in March
04/29/2024 | IPCIPC announced the March 2024 findings from its North American Electronics Manufacturing Services (EMS) Statistical Program. The book-to-bill ratio stands at 1.31.
Real Time with… IPC APEX EXPO 2024: A Global Presence in PCB Manufacturing
04/29/2024 | Real Time with...IPC APEX EXPORob DiGiovanni, VP of sales for the Americas at STARTEAM Global, discusses the company's global presence in PCB manufacturing. As he explains, the firm operates facilities across Europe, Asia, and North America, specializing in serving contract manufacturers in the automotive and medical industries. They emphasize quality and meeting OEM standards, focusing on offshore supply and non-Chinese factories in the North American market. The company has grown through acquisitions and rebranding to offer multiple products.