The stencil printing process is one of the most critical processes in the electronic production. Due to the requirement: “faster and smaller” it is necessary to place components with different paste volume close together without regard to solder paste printing. In our days it is no longer possible to control the solder paste volume only by adjustment of the aperture dimensions.
The requirements of solder paste volumes for specific components are realized by different thicknesses of metal sheets in one stencil with so called step stencils. The step-down stencil is required when it is desirable to print fine-pitch devices using a thinner stencil foil,but print other devices using a thicker stencil foil.
The paper presents the innovative technology of step-up and step-down stencils in a laser cutting and laser welding process. The step-up/step-down stencil is a special development for the adjustment of solder paste quantity,fulfilling the needs of placement and soldering. This includes the laser cutting and laser welding process as well as the resulting stencil characteristics and the potential of the printing process. Influencing factors on the printing process for step stencils like squeegee speed,squeegee angle,squeegee pressure,squeegee material,printing direction and distance from the step-edge to the nearest aperture are shown in this paper. A test layout was developed with different step heights and different distances from the nearest apertures to the step-edge to give proposals and guidelines for future designs. The transferred solder paste volume was measured with highly sophisticated systems and the results which are gained in this study allow new design guidelines.
The focus of this paper is on the printing performance of step-up/step-down stencils and the paper ends up with a short outlook on 3D cavity printing.

Considering technological advances in multi-depth cavities in the PCB manufacturing industry,various subtopics have materialized regarding the processing and application of such features in device manufacturing.
In a previous paper the topic of solder paste printing on PCBs on standard SMT equipment and with multiple cavity depths was investigated. The success of solder paste printing is a prerequisite for further assembly and reliability of the entire electronic construct. In this paper we intend to examine the overall manufacturability and subsequently analyze the reliability of multi-depth cavity PCBAs,presupposing the presence of solderable features within these cavities.
The intended methods of evaluation for manufacturability will be the evaluation of solder paste volume (PV) and warpage performance.
The intended methods of evaluation for reliability will be the evaluation of mechanical loading (drop test) and thermal loading (TCT,reflow) on PCBA test vehicles.
The aim of these investigations is to identify any possible criteria of a solderable multi-depth cavity PCB,which may affect manufacturability and/or reliability,and if so to which magnitude. Thus,we expect to locate general and possibly specific advantages and/or limitations of such a product under a standard manufacturing environment.
In an effort to achieve a broader understanding of the entire process and product scope,the participants in the trial are an HDI PCB manufacturer,stencil manufacturer and a global EMS manufacturer.

With the miniaturization of components in the semiconductor industry,the need for specialized solder pastes with finer
powder mesh sizes for package-on-package (PoP) assemblies has become imperative and increasingly more common. As the
powder mesh size decreases (smaller diameter powder),more surface area of powder within the paste is exposed and,
therefore,more susceptible to oxidation. The flux vehicle of the solder paste consequentially has more oxides to remove in
order to allow for proper coalescence to form a good solder joint. The intent of this paper is to evaluate whether the decreased
powder mesh size and increased oxide content of the powder in the PoP pastes affects the voiding performance of the
materials,and to what degree.

The Surface Mount Technology (SMT) industry has been faced with several challenges in the past decades. Two of the most recent ones are RoHS compliant lead-free assembly and the adoption of fine-pitch components assembly processes. Moreover,halogen-free is another new requirement for assembled PCB reliability,environmental and health concerns. All these requirements create fundamental challenges of developing a solder paste to satisfy everything. One of the resolutions for these challenges can be the development of the activator package with the advanced organic chemistry technology.
Serial innovative activator system was developed recently for solder paste flux,tacky flux and liquid flux formulation. This paper will discuss three Type 4 lead-free halogen-free no-clean solder pastes (ROL0) developed based on different innovative activators,which respond to the challenges described above. The printing performance,coalescence,wetting,BGA voiding and head-in-pillow characteristics,are compared and discussed in detail. The testing results show all three pastes with the new activators are fully capable of printing and reflowing 01005 components with different board/device finishes,even in air reflow. They can handle a wide variety of print variables,including print speed,long abandon time and a wide range of temperature and humidity. Post-soldering,the paste offers minimized defects,including head-in-pillow and BGA voiding.

•What is Digital Printing
•Ink Jet Technology
•Printing SM using Ink Jet
- Highlights
- Zero clearance technology
- Product improvements
- PCB shops,end users and designers Benefits

- DD Detector is State of the Art
- Software: Addressing all measurement challenges; Measurement Results for Au,Pd and Ni(P),independent of substrate material
- Traceability and Reproducibility through Reference Standards
- XRF-Instrument considerations
- Comparison of Spectra

Atmospheric dust consists of solids suspended in air. Dust is well known for its complex nature. It normally includes inorganic mineral materials,water soluble salts,organic materials,and a small amount of water. The impact of dust on the reliability of printed circuit board assemblies (PCBAs) is ever-growing,driven by the miniaturization of technology and the increasing un-controlled operating conditions with more dust exposure in telecom and information industries.
A fundamental and systematic study on the impact of dust is needed,since not much research has been done in this area. We started by asking some basic questions on dust. Since dust is always present in the atmosphere,under what conditions is dust a reliability concern for electronics? What are the key characteristics of dust? Are some dust types worse than others: e.g.,dust that is more hydrophilic? Should there be classifications of dust? How will different combinations of dust,voltage,relative humidity (RH),temperature,and other factors affect electronic materials and circuits? This paper presents some results towards answering these questions. We designed a group of experiments using real life dust collected from both indoor and outdoor areas. AC impedance spectroscopy (IS) was employed as the measurement technique for this research. We designed test coupons with adjustable spacing between electrodes and measured their electric properties under different relative humidities. We analyzed aqueous solutions produced from dust samples were using their pH and conductivity. And we further analyzed the compositions of the dust samples. We found that dust had a significant impact on the reliability of PCBA. Relating the test results to the analysis results,indoor dust is more sensitive to the change of relative humidity compared to outdoor dust due to the water soluble salts and particle size. At the same dust deposition density,indoor dust is more susceptible to induce moisture related failure,such as loss of surface insulation resistance,electrochemical migration,and corrosion.

Silicone contamination is known to have a negative impact on assembly processes such as soldering,adhesive bonding,coating,and wire bonding. In particular,silicone is known to cause de-wetting of materials from surfaces and can result in adhesive failures. There are many sources for silicone contamination with common sources being mold releases or lubricants on manufacturing tools,offgassing during cure of silicone paste adhesives,and residue from pressure sensitive tape. This effort addresses silicone contamination by quantifying adhesive effects under known silicone contaminations. The first step in this effort identified an FT-IR spectroscopic detection limit for surface silicone utilizing the area under the 1263 cm-1 (Si-CH3) absorbance peak as a function of concentration (ug/cm2). The next step was to pre-contaminate surfaces with known concentrations of silicone oil and assess the effects on surface wetting and adhesion. This information will be used to establish guidelines for silicone contamination in different manufacturing areas within Harris Corporation.

For the last couple of years,the main concerns regarding the electrical performance of blank PCB boards were impedance and ohmic resistance. Just recently,the need to reduce insertion loss came up in discussions with blank board customers.
One approach to alleviate the issue is the change to a lower loss dielectric material. Hence the percentage of boards that require a lower loss material is increasing significantly.
However,changing to a lower loss material influences PCB cost and in addition may affect the reliability of the boards.
The second way to reduce insertion loss is to minimize the conductor roughness. The roughness is influenced by two factors: the initial roughness of the copper foil (as received) and the treatment of the copper surface prior to lamination (a.k.a the oxide replacement).
Our first investigation,presented at Apex 2011,focused mainly on the influence of a wide variety of oxide replacements. The main focus of this follow on investigation is copper foil quality. Several very low profile and ultra low profile copper foils were investigated in a DOE,together with two types of oxide replacements.
The resulting electrical performance characteristics,like impedance,DC line resistance and insertion loss were evaluated in an ANOVA approach.
The paper describes the test vehicle and the testing methodology and discusses in detail the electrical performance characteristics. The influence of the independent variables on the performance characteristics is presented.
Finally the thermal reliability of the boards built applying different copper foils and oxide replacements was investigated.

Specification and control of surface roughness of copper conductors within printed circuit boards (PCBs) are increasingly desirable in multi-GHz designs as a part of signal-integrity failure analysis on high-speed PCBs. The development of a quality-assurance method to verify the use of foils with specified roughness grade during the PCB manufacturing process is also important.
Currently,there is no method for adequately quantifying roughness of a signal trace or a power/reference plane layer within a finished PCB. The measurement methods currently available can only be applied to the base foil,prior to its incorporation into a finished board,as they require direct access to the surface to be measured. In a PCB,this surface is not directly accessible,as it is encapsulated within the board,and attempting to expose the surface will necessarily damage or destroy both the board and the surface of interest.
This paper describes a method by which the surface roughness of a metal foil or conductor layer within a PCB may be determined from a microsectioned sample of the same. A small,non-functional area,e.g. a corner of the PCB,can be removed,and the surface roughness of the circuit layers can be assessed without impairing the function of the PCB.
In the proposed method,a conductor (a trace or a plane) in the microsectioned sample is first digitally photographed at high magnification. The digital photo obtained is then used as an input to a signal- and image-processing algorithm within a graphical user interface (GUI). The latter automatically computes and returns the surface roughness values of the layer photographed. The tool enables the user to examine the surface textures of the two sides of the conductor independently. In the case of a trace,the composite value of roughness,based on the entire perimeter of the trace cross-section can be calculated.