Organic Solderability Preservative (OSP) coatings feature among the leading surface finish options in the printed circuit board (PCB) industry because of their excellent solderability,lead-free applicability,ease of processing,and low cost. OSP coatings are primarily composed of organometallic polymer with small molecules such as fatty acids and azoles entrained during the coating deposition process. OSP coatings are deposited on the Cu features of PCBs. They are transparent across the visible spectrum and they typically range in thickness from about 0.1µm – 0.6µm.
UV-Visible absorption characterization is the most frequently used technique to estimate OSP coating thickness. This method requires that a control sample be sent through the OSP line and coated with OSP. This OSP layer is then removed from the control sample using organic solvents,the solution is analyzed,and the thickness of the original coating is inferred. The OSP thickness on the active PCB is assumed to be equivalent to that of the control sample. The method is indirect,destructive,requires control samples,and does not yield any information concerning the uniformity of the coating. Furthermore,the wet-phase preparation steps make this technique susceptible to large experimental errors.
In this contribution the use of Optical Reflectivity for direct OSP metrology will be explored. Optical Reflectivity measurements are completely non-destructive,differentiating them from other technologies used to measure OSP thickness. Typically,the small probe area ensures that individual PCB features or regions of interest can be chosen for analysis. The non-destructive nature of the measurement ensures that quantitative data from OSP coatings can be collected at any time during the PCBs lifecycle. Adverse effects due to production steps and ageing on the OSP film can readily be measured. Control samples and test coupons become redundant and the circuit board itself does not require any sample preparation following OSP deposition.

Advancements and evolutions in printed circuit board manufacturing,design,and electronics assembly have driven new research on high temperature organic solderability preservative (HT OSP) surface finishes. More specifically,developments in OSP chemical processes are aimed at producing a durable finish which ensures that a board surface retains solderability through more challenging and harsh Pb-free assembly conditions. From this,it is clear that advancements in OSP processing and coating performance require a solid understanding of the mechanisms associated with coating formation and thermally driven degradation. This work examines and describes OSP structure and composition and how it is affected by heat treatments. Additionally,mechanisms of degradation of OSP are proposed along with possible strategies to remedy it.

With the increased use of lead-free alloys there has been interest in understanding the applications and limitations of final finish coatings for lead-free assembly processes. The higher temperatures needed for lead-free assembly make it more challenging to provide good protection of the underlying copper surface while maintaining acceptable solderability. Coatings that provided good solderability when using eutectic solder may no longer be acceptable when using lead-free alloys. This is especially true when multiple lead-free reflows are incorporated into the assembly process. Coatings that stand up to eutectic solder reflow temperatures may degrade or tarnish when exposed to lead-free reflow temperatures. The purpose of this paper is to provide information on the applications and limitations of OSP and immersion silver coatings in lead-free assembly processes. Solderability testing included evaluation of hole fill and wetting balance performance using SAC 305 solder. Solderability was evaluated on panels as coated as well as after durability testing. Solderability testing after multiple reflows was conducted to simulate production requirements. Surface preparation prior to application of the final finish coating was studied and included evaluation of etch type.

In general,new lead-free solder alloys with the following characteristics are desired in order to enable the continuation of miniaturization trend: (1) alloy with a reduced melting temperature,(2) alloy with a better solder spread,(3) alloy with a slower wetting speed at melting temperature,(4) a softer alloy,or alloy with a reduced voiding tendency or greater ductility,(5) alloy with a refined grain size,(6) alloy with low tendency to form large IMC plate,(7) alloy with a higher resistance toward corrosion and electrochemical migration,(8) alloy with a greater oxidation resistance. On the other hand,no-clean fluxes with the following features are needed: (1) reduced volatile,(2) halide-free,(3) greater fluxing capacity,(4) higher residue resistivity,(5) more resistant to oxidation and charring,(6) more efficient oxidation barrier,(7) lower activation temperature,(8) slower wetting speed when solder begins to melt,(9) less spattering,(10) higher probe penetratability,(11) capability of inducing nucleation of solder upon cooling,and (12) greater resistance against slump.

The change to lead-free solders has forced the electronics industry to consider more than it ever has before what properties are important in a solder. When the tin-lead eutectic was the only solder considered in most applications it was a matter of adapting products and processes to the properties of that alloy,taking advantage of its strengths and designing around its weaknesses. With what seemed like an almost unlimited range of options the electronics industry faced a dilemma when it had to choose a lead-free solder to replace the tin-lead solder that it had relied on ever since there was an electronics industry. The initial concern was melting point as it was considered essential that the replacement alloy have a melting point as close as possible to the 183°C of the tin-lead eutectic. It has since been found that higher melting point alloys can be used without a pro rata increase in process temperature. The higher yield point of most lead-free solder options seemed initially to be a bonus but it has subsequently been realised that in some circumstances compliance is more important than strength. Although some properties of tin-lead solder have turned out to be not as essential in a lead-free solder as initially expected other properties are turning out to be as important in a lead-free as they were in tin-lead. Solidification behaviour and fluidity are two examples of such properties and it has been found that lead-free solders that match tin-lead solder in that regard offer measurable performance advantages. In this paper the authors will review the solder properties they consider important in a lead-free solder and report the results of measurement of these properties in a range of lead-free solders currently used or under consideration for commercial production.

When trying to achieve 40 microns of placement spacing,bridges and tombstones may occur due to the variation of the component dimensions,equipment accuracy and pickup position variations.
Hawse have developed and patented a new process to achieve this type of spacing. This new process will be described in this paper.
Mounting components on product with 40 microns (1.6 mil) spacing is difficult due to material variations; so it is necessary to expand the spaces for mounting. By design the print deposits are shifted to the right and left of the pads. Solder paste deposits are then applied off the center of the pads. The system measures this misalignment for each deposit and feeds forward this information to the placement machine or machines to shift the placement position to match the location of the solder paste.
Controlling the position of the solder paste is very important to prevent bridges. The allowable tolerance for misalignment is about 30 microns and constantly maintaining this accuracy is extremely important. The system measures the position of the solder paste and feedbacks this information to the screen printer to maintain a constant solder paste position. Therefore it is imperative that the print position be constantly monitored. The printing condition of solder paste is controlled with the feedback feature of the system.
This system uses the properties of self-alignment of the solder paste to achieve the final result of 40 microns placement spacing. Self-alignment can be used with lead free solder paste by setting the proper reflow conditions or temperature profiles.

The trend towards ever smaller components and more function density continues unabated in the SMT field. Manufacturers and users must increasingly coordinate their activities to develop usable and cost-effective solutions. Progress doesn’t stop,especially in the world of electronics. Electronics are used in a wide variety of applications. More and more functions are being crammed into ever smaller modules. To master these challenges on the path from SMD technology to the world of microelectronics,it is no longer enough to simply make the components smaller. Instead,the engineers must analyze the interactions between materials and take them into account for their manufacturing processes. In order to achieve good manufacturability all parties,starting with the designer,the PCB-manufacturer,the printer-,stencil- and solder paste maker,as well as the Pick & Place equipment manufacturer and the reflow expert should be consulted. Only a common effort will ensure good quality.

In 2006 we conducted two formal detailed experiments on the 01005-component assembly process. Two of the most significant findings from those experiments were that a 0.003” thick stencil is required to achieve an acceptable solder paste release percentage and that nitrogen is required for complete reflow of the very small volume of solder paste. For the most part,several other researchers had concluded the same for 01005 component assembly experiments.
Both the potential requirement to use nitrogen for the reflow soldering process and the use of a 0.003” thick stencil will be a major issue for high volume manufacturers. Introduction of Nitrogen will increase the cost and the use of a 0.003” stencil may cause insufficient solder paste for larger components on the same board.
The focus of this study is to discover methods to avoid the use of nitrogen in the reflow soldering process and to allow the use of a 0.004" thick stencil in the solder paste printing process. The questions that will be answered are:
- Can any available stencil technologies and solder paste product/type provide sufficient solder paste release to allow the use of a 0.004" thick stencil for 01005 components?
- Can we develop reflow profiles that will completely reflow 01005 components in an air atmosphere and/or are the solder paste suppliers developing new products that will allow the extremely small volumes of solder paste printed for 01005 components to be reflowed in an air atmosphere?
- If the use of nitrogen is required what is the optimum oxygen level to get complete reflow?

The mobile communication devices such as cell phones require high speed transmission of large volume data as well as reduction in size and weight. When signal is transmitted in high speed and frequency on PWB,signal integrity becomes a big problem. One of the most widely used methods to tackle the problem is to apply low Dk/Df materials. Even though various materials are available for that purpose,they tend to be quite expensive and require special care during the fabrication process. Therefore,PWB fabricators have been looking for more affordable and easily processable low Dk/Df material. To meet these demands,a novel PWB material has been developed. The special epoxy resin with rigid backbone was used,which does decrease Dk level but not significantly for the application. Therefore,hydrophobic hardener was adopted to compensate the difference in dielectric properties. The resulting material has Dk of 3.8 at 1 GHz,which is 10% lower than that of conventional FR-4. In addition,its Tg is higher than 170 C. It also shows an excellent thermal stability,withstanding longer than 30 minutes at T-288. The further development of material toward better dielectric properties was made possible with application of NE glass instead of conventional E glass. The resulting laminate has Dk of 3.5 as well as a Df of less than 0.01. The other properties of these materials,such as migration property,Td and reliability will be presented.

We demonstrate here a novel CCL (Copper Clad Laminate),which exhibits an extremely low transmission loss at mm-wave band. The CCL,which we developed,is based on a new fluoropolymer with adhesive characteristics. In contrast to conventional PTFE,the adhesive fluoropolymer allows us to apply a wholly dry process for CCL fabrication,which contributes to environmental load reduction.
It is well known that the factor of transmission loss mainly consists of conductive loss and dielectric loss. However,in conventional CCL data sheets,only the loss tangent data at specific frequencies are disclosed. Neither the dielectric loss nor the whole transmission loss at the other frequencies is known. In order to minimize the transmission loss at mm-wave band,the quantitative analysis for those factors is essential.
We proposed the evaluation method,which can clarify not only the dielectric loss but also the conductive loss of CCL up to 110GHz. Several transmission lines with different impedance were measured and analyzed; the three different losses were discriminated in straightforward manner. Besides the evaluation method,a highly accurate measurement technique for low loss transmission line was achieved.
Using several kinds of surface roughness of copper foil,we made CCL test samples and evaluated the transmission loss by the above-mentioned method. Since the results indicated that the surface roughness of copper foil remarkably influenced the transmission loss,profile free copper foil was used for developed CCL. Due to the adhesive characteristics of new fluoropolymer,enough peeling strength was obtained without extra surface treatment.
Finally we benchmarked our developed CCL to the Rogers RT/duroid 5880,with the world’s lowest loss characteristics,and the result showed improved loss characteristics compared to RT/duroid 5880.