Design, Simulation & Prototypes

• Reducing Costs Through Thermal Simulation
  by Dr. John Parry, CEng., Mentor Graphics Mechanical Analysis Division (formerly Flomerics)
  
  Stacked modules are becoming increasingly popular, with thermal management being a critical consideration in most stacked module applications because of their power density. We take a look at a specific case in which a stacked module had to be developed for a critical defence application. Thermal simulations on the initial concept design highlighted the defects of the design and enabled engineers to select the least expensive potting compound that would meet the thermal requirements of the application.

PCB Fabrication

• Nano- And Micro-Filled Conducting Adhesives For Z-axis Interconnects
  by Rabindra N. Das, John Lauffer, Frank D. Egitto and Voya Markovich, Endicott Interconnect Technologies
  
  We take a look at micro-filled epoxy-based conducting adhesives modified with nanoparticles for z-axis interconnections, especially as they relate to package level fabrication, integration, and reliability. A variety of conducting adhesives with particle sizes ranging from 80 nm to 15 µm were incorporated as interconnects in printed wiring board (PWB) or laminate chip carrier (LCC) substrates. SEM and optical microscopy were used to investigate the micro-structure, and conducting and sintering mechanisms. Volume resistivity of nanoparticle-modified adhesives is in the range of 10-5 to 10-6 ohm-cm. The present process allows fabrication of z-interconnect conductive joints having diameters in the range of 55-300 microns. There was no delamination of conductive joints after 3X IR-reflow (assembly precondition), pressure cooker test (PCT), and solder shock. The processes and materials used to achieve smaller feature dimensions, satisfy stringent registration requirements, and achieve robust electrical interconnections are discussed.

Automotive Electronics

• Going ‘Off The Curve’ With Polymers For Thermal Interface Materials
  by Sara N. Paisner, Ph.D., Lord
  
  Smaller and faster silicon devices have made heat dissipation at the die package level a critical issue in some applications, with the cooling capabilities of package designs still limiting device performance. In order to improve heat dissipation from these new packages, higher thermal conductivity Thermal Interface Materials (TIMs) are necessary. Increasing thermal conductivity in TIMs typically requires making trade-offs in other areas, such as viscosity or rework-ability. New technical developments have made it possible to go ‘off the curve’ of traditional tradeoffs to design highly thermally conductive TIMs. These new TIMs have high thermal diffusivity, as well as low modulus and high adhesion, which are required for newer, smaller form factor, higher power packages in current and future automotive and microelectronics applications.

• The Route To Cleaner Electronics In The Automotive Industry
  by Sheila Hamilton, Teknek
  
  There are few areas of electronics where the demand for reliability, performance and zero tolerance of defects is higher than in the automotive sector. From ABS systems to satellite navigation, electronic systems are now at the core of the car industry. A key barrier to achieving zero defects is the presence of contamination in the electronics production environment. We take a look at the problems caused by contamination and the solutions being adopted by electronics manufacturers.

• Halogens And Halides
  by Chrys Shea, Cookson Electronics
  
  Halogens are found in many electronic components and are the focus of systematic regulatory elimination. In many cases there are no simple drop-in replacements for halogenated materials. Halides, ionic compounds that contain halogens and are often used electively in fluxes to improve soldering performance, may also be subject to elimination in the foreseeable future. The use of halides in fluxes is optional, but some difficult solderability situations demand them. With all the buzz lately about halogen-free and halide-free products, we take a quick look at what halogens and halides are and answer questions such as: what do halogen-free and halide-free actually mean? Why do we want to get rid of them? And why do we use them at all?

• Design For Testability – The Importance Of Simple Solutions
  by Holger Göpel, Göpel electronic
  
  While PCB component complexity and density continues to increase, making it easier to create defects and more difficult to find them, quality requirements remain the same: faulty assemblies must not be delivered to clients. In this scenario, we take a look at the evolution of test methodologies and the best approaches for the assembled boards of the future.

Advanced Soldering

• High First-Pass Yields In A Lead-Free Environment
  by Mario Scalzo, Indium
  
  With the decrease in both the size and the pitch of area-array devices, new problems may arise in both printing and flux technology, such as head-in-pillow and graping defects. Print transfer efficiency of the solder paste must be maximised and flux activators have to be redesigned for high-tin alloys. We take a look at a statistical approach to formulating solder paste rheology and flux chemistry resulting in high print efficiencies and appropriate activity release to produce high first-pass yields.

Assembly

• Preventing Corrosion Of PCB Assemblies
  by Donald Cullen, MacDermid
  
  Corrosion is an inevitable fact in our increasingly polluted environment. Corrosion can be mitigated in several ways. The materials used in the manufacture of electronic devices need to be chosen wisely, based on available corrosion data. The materials should be protected from pollution by the use of protective coatings, device enclosures, or relocation of equipment to more protected environments. Humidity is a chief contributor to corrosion, as water allows intimate access of concentrated contaminating species and transportation of corrosion products. The choice of protective films needs to be weighed against other functional aspects of the film choices. Materials used in electronics manufacture will interact with different pollutants at differing rates based on pollutant levels and other environmental effects. In some cases, galvanic pairs can be created when using dissimilar materials, which can accelerate corrosion. To predict corrosion, and useful service life of electronic devices, historical data set can be consulted, but gaps exist in the rate of corrosion on surface finishing materials used in today’s electronics. To fill in data gaps, industry groups can share resources in studying corrosion. New findings will allow for better predictability on service life, selection of appropriate coatings to fit specific needs, and development of more robust materials to protect circuitry.

• Selecting An Optimum Cleaning Process
  by Martina Stieglmeier, Sandra Pilz, Zestron
  
  When searching for the optimal cleaning process, users must ask themselves numerous questions, as there is no one-size-fits-all solution. In fact, elements such as the cleaning medium and the cleaning machine must be adapted to the specific requirements. The required surface cleanliness is, for example, much higher for assembly cleaning than for stencil cleaning, which results in more stringent requirements on the cleaning chemicals and machine. As the market offers a wide range of different cleaning systems, an independent expert with a representative selection of cleaning machines, cleaning media and analytical methods at their disposal can carry out cleaning trials for the customer to facilitate the user in making the right investment decision.