Underfilling is a long-standing process issued from the micro-electronics that can enhance the robustness and the reliability of first or second-level interconnects for a variety of electronic applications. Its usage is currently spreading across the industry fueled by the decreasing reliability margins induced by the miniaturization and interconnect pitch reduction. While material and processing aspects keep pace with the fast technology evolutions,the control of the quality and the integrity of under filled assemblies remains challenging in some cases,especially when considering non-destructive inspection techniques and board-level underfilling. In particular,Scanning Acoustic Microscopy (SAM) which is routinely used for the control of under filled flip-chips turns out to be almost ineffective for usual BGA devices due to the presence of the component PCB substrate. This paper will address the control of surface mount under filled assemblies,focusing on applicable inspection techniques and possible options to overcome their limitations.

The challenge for 3D IC assembly is how to manage warpage and thin wafer handling in order to achieve a high assembly yield and to ensure that the final structure can pass the specified reliability requirements. Our test vehicles have micro-bumped die having pitches ranging from 60um down to 30um. The high density of pads and the large die size,make it extremely challenging to ensure that all of the micro-bump interconnects are attached to a thin Si-interposer. In addition,the low standoff between the die and interposer make it difficult to underfill. A likely approach is to first attach the die to the interposer and then the die/interposer sub-assembly to the substrate. In this scenario,the die/interposer sub-assembly is comparable to a monolithic silicon die that can be flip chip attached to the substrate. In this paper,we will discuss various assembly options and the challenges posed by each. In this investigation,we will propose the best method to do 2.5D assembly in an OSAT (Outsourced Assembly and Test) facility.

The world of electronics continues to increase functional densities on products. One of the ways to increase density of a product is to utilize more of the 3 dimensional spaces available. Traditional printed circuit boards utilize the x/y plane and many miniaturization techniques apply to the x/y space savings,such as smaller components,finer pitches,and closer component to component distances. This paper will explore the evolution of 3D assembly techniques,starting from flexible circuit technology,cavity assembly,embedded technology,3 dimensional surface mount assembly,etc. We will explore various technologies available today and some that are starting to appear. This paper will illustrate some of the key items for each technology and what some of the key challenges would apply. The assembly processes needed for each of these areas will be touched upon and what items will be needed to be enhanced for continuing the drive to better utilization of the z axis area available on pcba processing.

No-Fault-Found (NFF) events occur when a system level test,such as built-in test (BIT),indicates a failure but no such failure is found during repair. With more electronics continuously monitored by BIT,it is more likely that an intermittent glitch will trigger a call for a maintenance action resulting in NFF. NFFs are often confused with false alarm (FA),cannot duplicate (CNDs) or retest OK (RTOK) events. NFFs are caused by FAs,CNDs,RTOKs as well as a number of other complications. Attempting to repair NFFs waste precious resources,compromise confidence in the product,create customer dissatisfaction,and the repair quality remains a mystery. The problem is compounded by previous work showing that most failure indications calling for repair action are invalid. NFFs can be caused by real failures or may be a result of false alarms. Understanding the cause of the problem may help us distinguish between units under test (UUTs) that we can repair and those that we cannot. In calculating the true cost of repair we must account for wasted effort in attempting to repair unrepairable UUTs. This paper will shed some light on this trade-off. Finally,we will explore approaches for dealing with the NFF issue in a cost effective manner.

The number one issue identified by the 2009 International Electronics Manufacturing Initiative (iNEMI) Boundary-Scan survey was problems with obtaining correct and compliant boundary-scan description language (.bsdl) files from the semiconductor industry for use in boundary-scan printed circuit board assembly (PCBA) test generation. The major conclusions from the survey were:
•The semiconductor industry needs to make a greater effort to produce correct and compliant BSDLs.
•A better job needs to be done verifying .bsdl file compliance to the implemented JTAG hardware.
Non-compliance is typically found when a test is generated and it doesn’t work! The consequences of not having correct and compliant .bsdl files to generate boundary-scan tests is the inability to generate boundary-scan based tests and if tests cannot be generated,the result is lower overall test coverage for PCBAs which results in higher manufacturing costs and lower overall product quality. The work presented here by the iNEMI Boundary Scan Phase 3: Investigation into Challenges of Using .BSDL Files project group takes a more comprehensive view of the problem by surveying the industry to determine if issues associated with .bsdl files identified in the 2009 iNEMI Boundary-Scan survey still exist (and if so to what extent) and to identify new issues.

As device density continues to maximize the PCB real estate the reflowing of neighboring components or damaging of heat-sensitive components in the rework process continues to cause problems. Devices either have to be removed,thereby reducing rework throughput,or devices get damaged during the reflow process if not shielded from the heat generated during rework. The shielding solutions used most commonly either cannot be delivered in a timely fashion or offer very limited protection to these heat sensitive devices. A new,flexible heat shielding solution is now available that can be easily modified by the users and is inexpensive enough to have on hand. Most importantly it is an effective way to reduce the temperature on nearby components during the reflow/rework process so that neighboring devices do not go into reflow. This study documents the relative effectiveness of this ceramic nonwoven material as well as different shielding materials in protecting neighboring components during PCB rework.

In the rework environment,most equipment and procedures are designed for low volume repair/rework process. When a high volume rework is needed,the challenges begin. For example,a long cycle time is required to perform ball grid array (BGA) rework. When we need to remove material,do pad dressing,pad inspection,paste printing and place a new BGA,those steps increase the amount of dedicated rework equipment. Some machines are used to remove material,others are used to do pad dressing and others to place a new BGA. This results in hundreds of rework tools and equipment on the production floor. That volume of rework consumes enormous amounts of resources,requiring process controls such as daily profiling and maintenance using excessive hours of human resources. In addition,the standard rework process has low yield and high scrap rates. The Selective Reflow Rework Process is an approach to improving the high volume rework process,increasing process capabilities and process repeatability by using a standard reflow oven of 12 zones,pick and place machinery,semi-automated printing gear and Solder Paste Inspection (SPI) implementations. This approach was able to reduce the amount of rework equipment by more than half. Our human resource requirements (indirect and direct labor) were cut by more than 50% and our rolled throughput yield increased from 68.9% to 84.14%. The Selective Reflow Rework Process is less reliant upon operators and has become a repeatable,stable rework process. To obtain this advantage and have a successful implementation of this technology,the process requires new controls for printing,and check points before proceeding to the next process step. The printing process has a major impact on the HiP reduction,optimizing solder paste transfer efficiency (TE) and establishing a real SPC that gives real time warnings of anomalies. By identifying challenging process key parameters,including paste height,printing technique,pallets design and thermal barrier protection of TH parts,this paper will discuss some aspects of the process optimization and changes made to improve the quality of the rework process.

The biggest problem with designing rigid-flex hybrid PCBs is making sure everything will fold in the right way,while maintaining good flex-circuit stability and lifespan. The next big problem to solve is the conveyance of the design to a fabricator who will clearly understand the design intent and therefore produce exactly what the designer/engineer intended. Rigid-Flex circuit boards require additional cutting and lamination stages,and more exotic materials in manufacturing and therefore the cost of re-spins and failures are very much higher than traditional rigid boards. To reduce the risk and costs associated with rigid-flex design and prototyping,it is desirable to model the flexible parts of the circuit in 3D CAD to ensure correct form and fit. In addition it is necessary to provide absolutely clear documentation for manufacturing to the fabrication and assembly houses. The traditional attempt most design teams use to mitigate these risks is to create a "paper doll" of the PCB,by printing out a 1:1 representation of the board and then folding it up to fit a sample enclosure. This has a number of issues: 1) The paper doll does not also model the 3D thickness of the rigid and flex sections. 2) The paper doll does not include 3D models of the electronic components mounted on the PCB. 3) This approach requires a physical sample of the final enclosure which may not yet be final in its design either. 4) If the mechanical enclosure is custom designed,a costly 3D print will be required for testing. This adds much time and expense to the project. As cool as 3D printers are,it's not a sensible use for them if the modeling can be done entirely in software. This paper discusses practical steps in two approaches to solve these problems,contrasting against the traditional "paper doll" approach above. In the first scenario,a 3D MCAD model of the PCB assembly can be created in the MCAD package where a "sheet metal" model can be generated for the PCB substrate model. This sheet metal model can be bent into shape in the MCAD software to fit the final enclosure and check for clearance violations. This is not the best approach but it is better than paper dolls. In the second scenario,a significant part of the enclosure or mechanical assembly model is brought from the MCAD package into the PCB design software,where the rigid-flex board outline can be designed specifically to fit with it. Rigid-flex layer stack sections can be defined and then flexible circuit areas have bending lines added. In the PCB design tool's 3D mode,the folds are then implemented to reveal where potential clearance violations and interference occurs. The PCB design can then be interactively modified to resolve the problems and check right away - without having to build any further mock-ups or translate design databases from one tool to another.

Sustainable product design and the task of bringing new,earth friendly products to market is a top priority for corporate leaders in the manufacturing industry. By not reaching their compliance and sustainability goals,manufacturers risk loss of market share,fines for non-compliance against regulatory directives and possible damage to their brand. Managing material disclosure information from the supply chain is one of their biggest challenges. On average,80% of manufactured products today are comprised of components sourced from suppliers. This means that if the manufacturer’s goal is to understand how sustainable or compliant their product is,they must first pull all of the supplied parts into the product picture before doing any type of sustainability or regulatory analysis. This is no small task,especially for manufacturers dealing with 100s to 1000s of suppliers and supplier parts within a deep multi-level supply chain. The increased need to sell products in global markets,where a large portion of the product contains components sourced from around the world,coupled with the trend for higher product complexity adds another layer of challenges to manufacturers in trying to gain holistic views of their products in order to check for compliance against regulatory and industry directives. The most complex and tedious part of compliance and sustainability is getting accurate and complete data from suppliers. Manufacturers will need to focus on supplier interaction and automation of that process using a multi-faceted and “best-practice” approach,which could include functions such as: email interaction,web portals,integration to on-line databases,engaging third party data collection agencies,general PLM framework capabilities to exchange different document types,support for industry standards and full material disclosure from suppliers. Using an enterprise PLM framework to automate the process of gathering and managing supplier disclosure data,manufacturers will not only benefit today in addressing current sustainability challenges and gaining a competitive edge,but also tomorrow in addressing future needs and requirements to produce earth friendly,innovative and compliant products.

•Introduction to printed and wearable electronics
•Flexibility testing challenges
•Proposals for flexibility testing
•Validation case studies
•Future work