Electronics manufacturers protect their circuit boards with conformal coatings. Conformal coatings serve as a barrier from environmental hazards and internal shorts,tin whiskers,and corrosion at the board level. Within conformal coatings different material chemistries specialize in shielding from an array of hazards and can be applied by multiple methods. The most common method is atomized spray which disperses the material into a fine mist. Alternatively,non-atomized coating controls the materials’ dispense shape while maintaining the original liquid form. While some applications demand atomized spray and other scenarios overlap between atomized and non-atomized coating,this paper focuses on the circumstances where materials are ideally suited for non-atomized,selective coating. Board manufacturers and their process engineers are tasked with effectively protecting the boards they produce. High-volume manufacturing recognizes optimized set-ups to improve dispense quality,process control,reliability,and repeatability,while reducing material costs. For high quality,accurate,and repeatable conformal coating with efficient throughput,large-scale manufacturers utilize automated selective coating. Selective coating is used to coat specific components or areas of a board while respecting keep out zones. To further increase transfer efficiency,selectivity,throughput,yield,and reduce masking and rework,a non-atomized process is worth consideration. At times the best way to achieve target results requires an effective team. This can be accomplished using two applicators with different dispense technologies. The first is a film coating applicator with a non-atomized dispense that delivers a clean edge definition and coats boards with broad passes up to 750mm/sec. This applicator can be paired with a precision jet applicator that has capability for dispensing discrete dots. This resulting combination enables high-volume manufacturers to create conformal coating programs to maximize control,reduce waste,increase throughput,selectively coat,and reduce rework. Adding process controls to an automated system provides accountability with traceability and process parameter maintenance. By pairing these two applicators the utility for non-atomized,selective systems will continue to grow.

As consumer products continue to reduce in price,pressure is placed upon the manufacturing of sub-components for improving cost. Back in the mid-1990s,jet valves for fluid dispensing in electronics assembly entered the market,displacing older technology with significantly higher dispenser productivity resulting from high flow rates and reduced up/down motion requirements. As jet valve technology has evolved,valve actuation systems have continued to improve,pushing toward higher jet frequencies and smaller jetted dot volumes. In recent years,equipment suppliers have started promoting piezo-driven jet valves with significantly higher frequencies than traditional pneumatic-driven jets. However,in many cases,the implied promise of higher productivity and lower production costs per part resulting from higher frequency jetting never fully materialized. In further studies,fluid flow rate and jet frequency are not always the largest levers to improve productivity in some applications. We will examine several fluid dispensing applications from PCB assembly to wafer-level packaging,and review the potential productivity enhancements from moving to higher frequency jetting. We will also review additional factors that may impact the realized production cost savings such as component part reliability considerations,process program layout,closed-loop process controls,and non-dispensing operations of the fluid dispenser. High-frequency,piezo-driven jets can add value to a number of high-volume production applications. However,the frequency specification of a jet valve should not be the primary factor considered when selecting a dispensing process. Rather,a holistic view of the production costs and factors affecting productivity and cost-effectiveness should be used in making such decisions. In this paper,we seek to elevate the conversation above the noise of ever increasing jet frequency to see the bigger picture and identify what ultimately matters for reducing production costs per part

An ever-increasing number of electronics assembly applications are using flip chip packages that require large volume underfill. Large volume underfill is typically defined as being for a die size greater than 12 x 12 millimeters and requiring the underfill volume to be >20 milligram (mg). These types of high volume,high speed,precise underfill processes in High Volume Manufacturing (HVM) are posing significant challenges to meeting higher Units per Hour (UPH) requirements; in some cases these requirements mean up to a 33 percent increase when compared to the previous year’s output. Streaming is gaining favor as a fast and robust non-contact dispense method for underfill; however,when streaming underfill over an extended time,the volume of material passing through the pump may cause problems that impact dot volume repeatability. This is due to the fluid pathway containing dead spaces,which trap the material,complicating flushing and contributing to fluid adhesion over time. Such dot volume fluctuations may lead to undesired fillet size variations,and result in defects. This paper examines proven methods of mitigating dot variations and providing for better maintenance,such that the large volume underfill process can be run without maintenance for more than 3 weeks,an unheard-of zero maintenance interval to date. This paper will also address the challenges faced during dispensing of large volume underfill in HVM,and how control of a number of variables affecting underfill dispensing can achieve up to 3 week zero maintenance intervals for higher throughput and process reliability.

•Nano-electronics potential
•Barriers to entry – and opportunities
•Examples
–Nano-solder
–Capacitor materials
–Graphene
•Opportunities for rapid commercialization?

The use of copper foils laminated to polyimide (PI) as flexible printed circuit board precursor is a standard practice in the PCB industry. We have previously described [1] an approach to very thin copper laminates of coating uniform layers of nano copper inks and converting them into conductive foils via photonic sintering with a multibulb conveyor system,which is consistent with roll-to-roll manufacturing. The copper thickness of these foils can be augmented by electroplating. Very thin copper layers enable etching fine lines in the flexible circuit. These films must adhere tenaciously to the polyimide substrate. In this paper,we investigate the factors which improve and inhibit adhesion. It was found that the ink composition,photonic sintering conditions,substrate pretreatment,and the inclusion of layers (metal and organic) intermediate between the copper and the polyimide are important. Ink factors include the intensity of photonic sintering. Better sintering leads to better cohesive strength of the nano copper layer. The ink solvent and the dispersant used to suspend the nano particles are significant both for adhesion and the colloidal stability of the dispersion. Pretreatment of the substrate by plasma roughening did not improve adhesion. We describe the effects of chromium and nickel interlayers which are typically used in standard foil laminates. Finally,we describe the types of peel testing used to assess adhesion.

Flux consumption for wave soldering tends to decrease,mainly due to its gradual replacement by reflow soldering methods (i.e. pin-in-paste) in many electronics applications. However,in several cases,wave soldering still remains a must,with an increasing share of “selective” soldering processes,either using wave frames with dedicated apertures or solder fountains. Such processes are more challenging for the fluxes in terms of reliability under operation,since some chemistries remaining on the printed circuit boards after soldering may promote corrosion. Thus,flux manufacturers had to adapt their formulations to minimize such issues while keeping an efficient activation level,with several types of alloys (tin-lead,tin-silver-copper and low/no-silver) and associated with the numerous types of finishes encountered. The paper will cover the types of flux used in the electronic industry according to their chemistry and activation level (rosin-based,halides,alcohol-based or water-based flux...),and their characteristics with reference to standards. The limits of current standards will be discussed in regards to the last generation solder fluxes. Then,the development of two low-residue new generation fluxes,an alcohol-based flux and a true VOC-free flux,will be described,according to requirements: the lab tests results (surface tension,spread tests,wettability tests...) will be presented and discussed. Reliability will be especially investigated through surface insulation resistance,electro-chemical migration test,ionic contamination as well as Bono tests to determine the candidates able to provide high processability combined with chemical inertness of residues. Finally,the performance of flux will be assessed through customer tests,involving several types of boards,finishes and different solder alloys and wave equipment.

No-clean soldering processes continue to dominate the electronics manufacturing world,especially amongst consumer-type electronics. For many years,type 3 was pretty much the “standard” solder paste particle size with a distribution of 25 – 45 microns (-325/+500 mesh). However,the ongoing trend toward ever-increasing miniaturization is putting pressure on solder paste manufacturers to produce solder pastes that can reliably print through smaller and smaller stencil apertures. While great advances have been made in solder paste flux technology to accommodate very small apertures,those advances alone cannot meet all the challenges of miniaturization. There is a point at which reducing the solder particle size becomes necessary in order to create solder pastes which can provide adequate transfer efficiency for small stencil apertures. As a result,many modern solder pastes are available on the market with particle sizes smaller than type 3 such as type 4 (20 – 38 microns),type 5 (15 – 25 microns),type 6 (5 – 15 microns),as well as non-IPC particle size distributions like type 4.5 (20 – 32 microns). Reducing the solder particle size for a given volume or mass of solder powder increases the total surface area. Therefore,reducing the particle size increases the surface area that the flux component of the solder paste needs to clean to cause good coalescence and wetting of the solder. The ingredients in the flux responsible for cleaning the surfaces are generically called activators. Because activators are corrosive in nature,they are one of the flux ingredients that can have a substantial impact on the electrical reliability of the flux residue. With decreasing solder particle size,resulting in increasing surface area,the flux has to work harder to clean these surfaces,consuming more of the activators while increasing the amount of activator/metal oxide interaction by-products in the flux residue. Therefore,everything else being equal,changing (reducing) the particle size is likely changing the contents of the flux residue. With this in mind,one must ask: Does reducing the particle size of a no-clean solder paste have a measurable impact on the electrical reliability of the flux residue? If so,is it substantial enough to be a cause for concern? This paper uses IPC J-STD-004B SIR (Surface Insulation Resistance) testing to examine these questions. Two commercially available Pb-free no-clean solder pastes with varying particle sizes,one halogen- containing and the other halogen-free,were tested to see if and how different flux chemistries respond to reduced particle size. All of the solder pastes in this study were submitted to the same common air Pb-free reflow profile.

When designing PCBs,solder paste selection is critical. Once a specific paste type and supplier are identified,the manufacturing process is developed and refined. Critical to the quality of the solder joint is an effective thermal profile. All solder paste suppliers recommend an appropriate thermal profile for specific paste in accordance with J-STD-004/005 (IPC TM-650). At a minimum,solder paste suppliers confirm that the recommended thermal profile produced have passing results for corrosion,SIR and electrochemical migration tests. However,these tests are performed on bare boards. As PCB surface density and component mass increases,is the recommended thermal profile sufficient to produce quality solder bonds and fully volatilize flux residues? Flux residues remaining on a PCB surface and/or component may be benign. However,if the residues are ionic in nature,they can lead to failure mechanisms including leakage current,electrochemical migration and dendritic growth. For high reliable applications that include No Clean or RMA solder paste,it is likely the PCBs are cleaned. If water soluble (OA) solder paste is selected,the PCB is certainly cleaned. An optimized cleaning process cannot address poor solder bonding,but it can remove ionic flux residues minimizing possible failure mechanisms. This study was conducted to assess the effect of thermal profile variations on flux residue formation. It was limited to No Clean solder pastes as this paste may or may not be cleaned. Six (6) different pastes were considered. The IPC-B-52 test vehicle was used for this study. For each reflow profile variation,two identical test vehicles were processed; one was cleaned and one was not. Each was subjected to SIR analysis. Test vehicles that were cleaned were processed using a spray-in-air inline cleaner with an aqueous based cleaning agent.

The electronic industry is currently very interested in low temperature soldering processes,such as using Sn/Bi alloy,to improve process yield,eliminate the head-in-pillow effect,and enhance rework yield. However,Sn/Bi alloy is not strong enough to replace lead-free (SAC) and eutectic Sn/Pb alloys in most applications. In order to improve the strength of Sn/Bi solder joints,enhance mechanical performance,and improve reliability properties such as thermal cycling performance of soldered electronic devices,the company has developed a series of low temperature solderable adhesives using solder joint encapsulant,which can be used for Sn/Bi soldering applications. These low temperature solderable adhesives can be dipped,dispensed,or printed. Can these low temperature solderable adhesives replace SAC application? Pull test and drop test have been conducted for comparison. The pull strength of low temperature solderable adhesive is very comparable to that of SAC alloy,but the drop test of solderable adhesives is much better than SAC alloy. The reliability of low temperature solderable adhesive including the thermal cycling performance will be discussed in detail.

The dissipation of heat from a power die,such as those used to drive the increasingly popular LED arrays,has traditionally been achieved by use of a thermal interface material (TIM) and a metallic heat sink. The performance of this system is usually limited by the capability of the TIM portion of the layers. In circumstances where the unit may be open to the environment,an additional housing is required which can further degrade the thermal performance of the system. By replacing the TIM,heat sink and protective housing with a single thermally conductive,protective thermoplastic overmold material,system performance can be maintained and the assembly process streamlined. In this paper,the processing and performance of such materials will be discussed. The isotropic nature of these materials allows heat dissipation not only in the vertical direction as with a traditional system,but also laterally,thus reducing hot spots and enhancing overall performance. Thermal models show that even a modest thermal conductivity (0.5 W(mK)-1) can reduce hot spots by over 30ºC compared to a regular low pressure molding (LPM) material. These materials retain the low melt viscosities typical of LPM materials and can easily be molded into a wide variety of shapes,allowing flexibility in the final form of the product.