Characterizing and Minimizing Voids in Quad Flat No-Lead Pack (QFN) Device Assembly Using Pb-Free Solder Alloys

2009 ◽  
Author(s):  
Rangaraj Dhanasekaran ◽  
Harish Gadepalli ◽  
S. Manian Ramkumar ◽  
Tim Jensen ◽  
Ed Briggs
Keyword(s):  
Void Formation ◽  
Primary Objective ◽  
Thermal Dissipation ◽  
Electrical Performance ◽  
Solder Paste ◽  
Die Attach ◽  
Aperture Opening ◽  
Free Solder ◽  
Small Form Factor ◽  
The Impact

Quad Flatpack No lead (QFN) packages have become a popular choice in electronics packaging due to its small form factor. They are also gaining rapid industry acceptance because of its excellent thermal and electrical performance. The bottom side of the QFN package has a large thermal pad. This exposed die attach pad effectively conducts heat to the PCB and also provides a stable ground connection. Effective soldering of this surface to the pad on the PCB is required for good thermal dissipation and component functionality. The exposed thermal pad presents various challenges during the surface mount assembly process. One major challenge is solder void formation. Voids are primarily formed due to the entrapment of volatiles in flux outgassing during the reflow process. The primary objective of this study is to determine optimal parameters to minimize void formation in QFN packages (QFN16, QFN20, QFN28 and QFN32), specifically the reflow profile, lead-free solder paste and stencil aperture opening for the thermal pad. A systematic DOE based approach was used to arrive at conclusions, using the ratio of void volume on the thermal pad to the actual volume of solder paste printed as the response variable. Various graphs are presented to understand the impact of different parameters. Interaction graphs are used to determine optimal settings for each parameter.

Voiding and Thermal Resistance Modeling and Characterization for a QFN Assembly

2010 ◽  
Author(s):  
Harish Gadepalli ◽  
Rangaraj Dhanasekaran ◽  
S. Manian Ramkumar ◽  
Tim Jensen ◽  
Ed Briggs
Keyword(s):  
Thermal Resistance ◽  
Void Formation ◽  
Primary Objective ◽  
Void Volume ◽  
Thermal Dissipation ◽  
Electrical Performance ◽  
Solder Paste ◽  
Resistance Response ◽  
Response Variable ◽  
The Impact

Quad Flatpack No lead (QFN) packages have become a popular choice in electronics packaging due to its small form factor. They are also gaining rapid industry acceptance because of its excellent thermal and electrical performance. The bottom side of the QFN package has a large thermal pad. This exposed die attach pad effectively conducts heat to the PCB and also provides a stable ground connection. Effective soldering of this surface to the pad on the PCB is required for good thermal dissipation and component functionality. The exposed thermal pad presents various challenges during the surface mount assembly process. One major challenge is solder void formation. Voids are primarily formed due to the entrapment of volatiles in flux outgassing during the reflow process. The primary objective of this study is to determine optimal parameters to minimize void formation in QFN packages (QFN16, QFN20, QFN28, QFN32 and QFN44), specifically the reflow profile, lead-free solder paste and stencil aperture opening for the thermal pad. A systematic Design of Experiments (DOE) based approach was used to arrive at conclusions, using the ratio of void volume on the thermal pad to the actual volume of solder paste printed, as the response variable. A theoretical thermal resistance response variable was also modeled to analyze the DOE parameters and the conclusions were similar to the void model. Various graphs are presented to understand the impact of different parameters. Interaction graphs are used to determine optimal settings for each parameter. A regression equation for relationship between the factors and the void volume is identified to predict void volumes for any given component, paste volume and paste transfer efficiency.

Quantitative Evaluation of Voids in Lead Free Solder Joints

2015 ◽  
Vol 772 ◽  
pp. 284-289 ◽  
Author(s):  
Sabuj Mallik ◽  
Jude Njoku ◽  
Gabriel Takyi
Keyword(s):  
Solder Bump ◽  
Solder Joints ◽  
Void Formation ◽  
Lead Free ◽  
Lead Free Solder ◽  
Solder Paste ◽  
X Ray ◽  
Size And Shape ◽  
Solder Bumps ◽  
Free Solder

Voiding in solder joints poses a serious reliability concern for electronic products. The aim of this research was to quantify the void formation in lead-free solder joints through X-ray inspections. Experiments were designed to investigate how void formation is affected by solder bump size and shape, differences in reflow time and temperature, and differences in solder paste formulation. Four different lead-free solder paste samples were used to produce solder bumps on a number of test boards, using surface mount reflow soldering process. Using an advanced X-ray inspection system void percentages were measured for three different size and shape solder bumps. Results indicate that the voiding in solder joint is strongly influenced by solder bump size and shape, with voids found to have increased when bump size decreased. A longer soaking period during reflow stage has negatively affectedsolder voids. Voiding was also accelerated with smaller solder particles in solder paste.

Methodology to Quantify Impact of Package Delamination on Performance of High-Side Smart Power Switch Design

2020 ◽  
Vol 2020 (1) ◽  
pp. 000015-000020
Author(s):  
Min Chu ◽  
Jie Chen ◽  
Abidur Rahman ◽  
Rajen Murugan
Keyword(s):  
Electrical Performance ◽  
Diagnostic Feature ◽  
Electromagnetic Modeling ◽  
Smart Power ◽  
Modeling Methodology ◽  
Power Switch ◽  
High Side ◽  
Die Attach ◽  
Power Switches ◽  
The Impact

Abstract Generally, IC packages with exposed pads have excellent thermal and electrical performance – assuming high fidelity and integrity of die attach material. However, reliability challenges associated with die attach impacts electrical performance of vertical power FETs for high-side power switches. As such, it is critical to quantify the impact of these challenges on high-side power switches operation, so that their protection and diagnostic feature circuitries can be properly designed for mission critical applications. In this paper we present on a package and PCB co-modeling methodology that was developed to assess impact of die attach integrity on performance of high-side power switch designs. We explain how electrical co-optimization of the system (viz. FET-Package-PCB) interactions, was achieved through a coupled circuit-to-electromagnetic modeling, simulation, and analysis methodology. Silicon laboratory measurements data that validate the modeling methodology will be presented.

The Benefits of Flux-Coated Solder Preforms in a QFN Assembly Process

2015 ◽  
Vol 2015 (1) ◽  
pp. 000827-000832
Author(s):  
Brandon Judd ◽  
Maria Durham
Keyword(s):  
Mechanical Properties ◽  
Form Factor ◽  
Solder Joint ◽  
Circuit Board ◽  
Electrical Performance ◽  
Solder Paste ◽  
Assembly Process ◽  
Circuit Board Assembly ◽  
Difficult Challenge ◽  
Small Form Factor

The use of bottom terminated components (BTCs) such as quad-flat no-leads (QFNs) has become commonplace in the circuit board assembly world. This package offers several benefits including its small form factor, its excellent thermal and electrical performance, easy PCB trace routing, and reduced lead inductance. These components are generally attached to PWBs PCBs via solder paste. The design of these components with the large thermal pad, along with the tendency of solder paste to outgas during reflow from the volatiles in the flux, creates a difficult challenge in terms of voiding control within the solder joint. Voiding can have a serious effect on the performance of these components, including the mechanical properties of the joint as well as spot overheating. Solder preforms with a flux coating can be added to the solder paste to help reduce voiding. This study will focus on the benefits of utilizing solder preforms with modern flux coatings in conjunction with solder paste to help reduce voiding under QFNs, as well as the design and process parameters which provide optimal results.

A Repeatable and Reliable Rework Process for Lead-Free Fine Pitch BGA’s

2005 ◽  
Author(s):  
Deepak Manjunath ◽  
Satyanarayan Iyer ◽  
Shawn Eckel ◽  
Purushothaman Damodaran ◽  
Krishnaswami Srihari
Keyword(s):  
Primary Objective ◽  
Lead Free ◽  
Process Window ◽  
Solder Paste ◽  
Ball Grid Arrays ◽  
Joint Reliability ◽  
Fine Pitch ◽  
Pros And Cons ◽  
Free Solder ◽  
Rework Process

Fine pitch leadless components, such as Ball Grid Arrays (BGAs) and Chip-Scale Packages (CSPs), are increasingly used in modern day circuitry to aid miniaturization. Assembling these surface mount components using lead-free solder pastes has been a subject of interest for the past several years. Reworking a BGA is complicated as the solder joints are hidden underneath the component. The process window available for the rework process is very narrow and there are number of other critical factors, which complicate and affect the repeatability of the rework process. Consequently, the primary objective of this research endeavor is to develop a reliable and a repeatable process to rework lead-free fine pitch BGAs. The process steps to rework a BGA are component removal, site redressing, solder paste/flux deposition, component replacement and reflow. This experimental study evaluates a number of alternatives for several rework process steps during the course of developing a reliable and repeatable rework process. Two alternatives for site redressing namely, (i) copper wick with soldering iron, and (ii) vacuum de-soldering methods are evaluated. Similarly the application of solder paste versus gel flux is compared. A localized reflow method for replacing the component at the SRT machine is developed and it is compared with forced convection in reflow oven. The pros and cons of using the two reflow methods and the effect of multiple reflows on solder joint reliability is discussed in the paper. A reliability study was conducted on the samples and the results are presented to compare the various alternatives.

Pb-Free Thin Small Outline Package (TSOP) Board Level Reliability Study

2009 ◽  
Author(s):  
Weidong Xie ◽  
Kuo-Chuan Liu ◽  
Mark Brillhart
Keyword(s):  
Solder Joint ◽  
Coefficient Of Thermal Expansion ◽  
Circuit Board ◽  
Solder Paste ◽  
Eutectic Solder ◽  
Qualification Testing ◽  
Free Solder ◽  
Board Level ◽  
The Impact

Thin Small Outline Package (TSOP) are one of the most commonly used surface mount components due to its low overall cost. Traditionally leadframe packages such as TSOP or Quad Flat Package (QFP) are less of a concern (if assembled with SnPb eutectic solder paste) about their long term reliability and often exempted from board level qualification testing as the mechanical compliance of metal leads mitigate the stresses due to the Coefficient of Thermal Expansion (CTE) mismatch between the package and Print Circuit Board (PCB). Therefore more attention has been put on the solder joint reliability of Pb-free Ball Grid Array (BGA) packages over leadframe packages while the industry is moving away from SnPb eutectic solder materials to meet RoHS regulatory requirements. The authors have observed that TSOPs if assembled with Pb-free solder materials could fail at very early stages during qualification testing (in some case as early as 300 cycles under standard 0°C to 100°C thermal cycling). Since most Pb-free solder materials such as SnAgCu are mechanically more rigid than SnPb eutectic solder material, higher stresses are expected be induced in solder joints during temperature excursions. Pb-free solder materials’ wicking behavior may also contribute to the early failures. In this study, long term reliability of a flash memory TSOP has been investigated. These tested TSOPs, assembled on 93mil-thick PCBs with SAC305 paste, are of two configurations: one with single die and the other with stacked quadruple dies. Some test vehicles have been thermally aged under four different thermal aging conditions to study the aging effect on Pb-free solder joint life. Finite element analysis (FEA) modeling has also been employed to further investigate the impact of other parameters such as die size, package size, and the number of dies that being stacked inside one package.

scholarly journals Evaluation of The Printability of Lead Versus Lead Free Solder Pastes

2021 ◽  
Author(s):  
Ala Al Robiaee
Keyword(s):  
Printed Circuit Boards ◽  
Lead Free ◽  
Solder Paste ◽  
Circuit Boards ◽  
Stencil Printing ◽  
Printed Circuit ◽  
Main Factors ◽  
Free Solder ◽  
Print Process ◽  
The Impact

As the global marketplaces consider mandating lead-free equipments, many questions arise about the impact and feasibility of replacing lead in printed circuit boards soldering applications. In this project, the results presented of a study on comparing the process of screening lead paste versus lead free paste parameters for regular stencil printing using standard manufacturing methods. The key process parameters studies were: squeegee speed, squeegee pressure, and screening yield for both types of pastes. Two solder paste formulations (lead paste and lead-free paste) were evaluated in this study. The analysis of the pastes deposit volumes showed that for normal manufacturing range of printer (screener) settings (speed and pressure) tested the two pastes performed the same. The results also showed that the squeegee speed has a greater effect on the printing process than the squeegee pressure. The tests clearly showed that the lead paste was affected more by setting changes compared to the lead free paste. Varying the print speed and pressure for type of pastes by observing the resulting printed paste volumes optimized screening parameters. This study confirms that a new stencil or stencil design is not needed for the lead free paste. However, this study recommends a change to the sitting of the screening print process. Stencil cleaning frequency is one of the main factors that impact the production rate in an SMT line. The project highlights new results that lead free paste throughput will be less compared to lead paste at the screening step. The number of rejected boards screened with lead free-paste exceeded normal manufacturing standards. As stencil cleaning is a must function, it was recommended to increase stencil wiping frequency when lead free paste [is] in use in order to obtain a consistent volume with less screening defect.

Evaluating the Effect of SMT Material & Process Variables on Voiding Under QFNs

2016 ◽  
Vol 2016 (1) ◽  
pp. 000711-000720
Author(s):  
Brandon Judd ◽  
Maria Durham
Keyword(s):  
Hot Spots ◽  
Mesh Size ◽  
Daily Basis ◽  
Circuit Board ◽  
Electrical Performance ◽  
Solder Paste ◽  
Process Variables ◽  
Circuit Board Assembly ◽  
Material Process ◽  
Small Form Factor

Abstract Voiding under bottom terminated components (BTCs), such as quad-flat no-lead (QFN) components, is a problem which many circuit board assembly houses face on a daily basis. Such components have become very popular in circuit board assembly due to many of their benefits, including their small form factor, excellent thermal and electrical performance, easy PCB trace routing, and reduced lead inductance. Outgassing of flux in the solder paste used to attach QFNs to the PCB during reflow causes voiding under the components, as the gasses cannot escape because there is virtually no standoff under the QFNs. Voiding can have several serious effects on the performance of QFNs including reduced mechanical strength of the solder joint and hot spots under the QFN thermal pad because the voids do not conduct heat well. There are many process methods which are utilized in an attempt to mitigate the voiding issue, such as windowpane stencil designs and reflow profile. In this study, we will evaluate the effect of several other variables on voiding under QFNs, including solder paste powder mesh size, PCB surface metallization, and the reflow environment.

Thermally and Electrically Enhanced Wirebond BGA

2013 ◽  
Vol 2013 (1) ◽  
pp. 000478-000483
Author(s):  
Burton Carpenter ◽  
Boon Yew Low ◽  
Leo M. Higgins ◽  
Sriram Neelakantan ◽  
Robert Wenzel ◽  
...  
Keyword(s):  
Flip Chip ◽  
Hold Time ◽  
Thermal Interface Material ◽  
Thermal Dissipation ◽  
Electrical Performance ◽  
Package Design ◽  
Die Attach ◽  
Bga Package ◽  
End Use ◽  
Set Up

Next-generation processors continue to demand more thermal and electrical performance from the package. Frequently, devices are designed into Flip Chip (FC) packages where the previous generations were in Wire Bond (WB) because FC typically provides superior thermal dissipation and lower package electrical parasitics than WB packages. However, FC packages usually have higher costs for mid-range IO (500–800). An Enhanced WB BGA package has been designed with improved thermal and electrical performance compared to the industry standard TEPBGA-2 (Thermally Enhanced PBGA type 2). The 500μm barrier of mold compound between the die and heatspreader in the TEPBGA-2 is a major impediment to heat flow out of the package. By contrast, the Enhanced WB package uses post-mold attachment of a heat spreader that is adhesively bonded to the mold cap and thermally coupled to the die using a 40μm TIM (thermal interface material). Improvements to substrate design rules and the die attach process that enabled the Enhanced WB design to shorten bond wires by 40% and improved electrical performance. Package thermal resistance, Theta-Ja, was verified by simulation and measurement to be 3C°/W lower than TEPBGA-2, that dissipates up to 15W in some end-use applications, approximately 2× the performance of TEPBGA-2. DDR set-up and hold time showed 30ps improvement by both simulation and measurement. This paper will present the package design, thermal and electrical simulation and measurement results.

scholarly journals Evaluation of The Printability of Lead Versus Lead Free Solder Pastes

2021 ◽  
Author(s):  
Ala Al Robiaee
Keyword(s):  
Printed Circuit Boards ◽  
Lead Free ◽  
Solder Paste ◽  
Circuit Boards ◽  
Stencil Printing ◽  
Printed Circuit ◽  
Main Factors ◽  
Free Solder ◽  
Print Process ◽  
The Impact

As the global marketplaces consider mandating lead-free equipments, many questions arise about the impact and feasibility of replacing lead in printed circuit boards soldering applications. In this project, the results presented of a study on comparing the process of screening lead paste versus lead free paste parameters for regular stencil printing using standard manufacturing methods. The key process parameters studies were: squeegee speed, squeegee pressure, and screening yield for both types of pastes. Two solder paste formulations (lead paste and lead-free paste) were evaluated in this study. The analysis of the pastes deposit volumes showed that for normal manufacturing range of printer (screener) settings (speed and pressure) tested the two pastes performed the same. The results also showed that the squeegee speed has a greater effect on the printing process than the squeegee pressure. The tests clearly showed that the lead paste was affected more by setting changes compared to the lead free paste. Varying the print speed and pressure for type of pastes by observing the resulting printed paste volumes optimized screening parameters. This study confirms that a new stencil or stencil design is not needed for the lead free paste. However, this study recommends a change to the sitting of the screening print process. Stencil cleaning frequency is one of the main factors that impact the production rate in an SMT line. The project highlights new results that lead free paste throughput will be less compared to lead paste at the screening step. The number of rejected boards screened with lead free-paste exceeded normal manufacturing standards. As stencil cleaning is a must function, it was recommended to increase stencil wiping frequency when lead free paste [is] in use in order to obtain a consistent volume with less screening defect.

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