The Surface Mount Technology (SMT) industry has overcome many challenges in the last 30 years,since its introduction in the 1980’s. One recent challenge has been the lead-free assembly. People have been working for more than ten years to address this challenge. While the industry is finally getting a good handle on the lead-free assembly process,another significant challenge has begun to surface. The most current challenge is the adoption of miniature components assembly process. Miniature components used today includes 01005,0201 passives to 0.3 mm-0.4 mm CSP and BGA.
By itself,miniature components have their own challenges,but when combined with larger components on the same board,the challenges multiply by several fold. To make matters worse,the design and functionality demanded by consumers require the placement of miniature passives next to larger,castle-like components. This creates a fundamental challenge in satisfying the solder paste need for both small and large components. Even though this is an industry-wide issue,no significant studies can be found in the literature. There are many different approaches that can be taken to address this issue. These include step stencil,augmented stencil printing process,multiple printing passes,etc.
In a recent publication,Speedline reported work done at a very basic level to understand the printing challenges associated with “Broadband Printing”. Broadband Printing is defined here as the printing process that satisfies the solder paste volume required for a PCB with both miniature and larger components existing side by side.
This paper will investigate the capability of a single thickness stencil to satisfy the paste requirement for mixed components board by creative stencil design. Some of the stencil design factors that will be explored will include over printing of larger components,using different stencil technology,and stencil thickness. In addition to the printing study,components will be placed and reflowed to access the solder joint character. The post assembly boards will be inspected by using IPC-A-610 standard for fillet characterization. In addition,X-ray inspection and mechanical strength test will be conducted to characterize the solder joint integrity.

Some of the new handheld communication devices offer real challenges to the paste printing process. Normally,there are very small devices like 01005 chip components as well as 0.3 mm pitch uBGA along with other devices that require higher deposits of solder paste. Surface mount connectors or RF shields with coplanarity issues fall into this category. Aperture sizes for the small devices require a stencil thickness in the 50 to 75 um (2-3 mils) range for effective paste transfer whereas the RF shield and SMT connector would like at least 150 um (6 mils) paste height. Spacing is too small to use normal step stencils.
This paper will explore a different type of step stencil for this application; a “Two-Print Stencil Process” step stencil. Here is a brief description of a "Two-Print Stencil Process". A 50 to 75 um (2-3 mils) stencil is used to print solder paste for the 01005,0.3 mm pitch uBGA and other fine pitch components. While this paste is still wet a second in-line stencil printer is used to print all other components using a second thicker stencil. This second stencil has relief pockets on the contact side of the stencil any paste was printed with the first stencil.
Design guidelines for minimum keep-out distances between the relief step,the fine pitch apertures,and the RF Shields apertures as well relief pocket height clearance of the paste printed by the first print stencil will be provided.

Choosing a solder paste can make or break an assembly process. By choosing the right solder paste for the application,you will achieve the highest process consistency and solder joint quality.
This paper covers the most significant issues in solder paste selection to meet the goals of manufacturing. The goals of any assembly operation are to maximize both quality and throughput while controlling costs. Quality is maximized by choosing a paste that has the best performance with the materials,geometry and heating processes used to manufacture a product. Throughput is maximized by picking a solder product that accommodates the optimal deposition and heating methods. Cost of production is a complex calculation that includes material,direct labor,inspection,rework,and scrap value. Quality and throughput play key roles in cost control.
Not all solder products are created equal,even if they seem the same according to their classification. Specialty solder pastes provide enhanced performance over off the shelf products. There are differences in wetting characteristics,void control,flux residue,alloy strength,alloy flexibility,and other performance measures that can all play significant rolls in achieving quality,throughput,and cost goals. The key is to identify the solder product that best accommodates the processes required to meet these goals.

At times,wave soldering or reflow involving the entire assembly are not applicable for soldering of components. Selective soldering techniques vary widely in their ability to produce high quality,reliable electrical and mechanical connections. Much of the variation occurs because the selective soldering techniques heat the pads and the materials surrounding them unevenly. It is necessary to heat the pads,contacts and solder to a temperature sufficient to melt the solder and form a good intermetallic layer at both interfaces with the solder,while at the same time not over heating and damaging the PWB and nearby components. In many cases,the heat source is from one side of the connection only which can result in a severe thermal gradient through the solder connection and within the components. The construction of the PWB itself plays a part in the heating of the structures to be soldered.
Newer,lead-free solders must be heated to higher temperatures than traditional tin-lead solders. Due to the differences in specific heat of the materials,the amount of heat energy necessary to raise the temperature and melt Tin-Lead solder can be significantly different from that of the commercial RoHS-Compliant solders used in today’s assemblies. This is not a problem with reflow ovens where the heat energy is replaced as fast as it is absorbed and can be considered infinite. The heating of the assembly is driven by a temperature difference between the oven air and the components. However,in other selective soldering techniques,such as hot air or heating via a focused light beam,the amount of energy is limited and must be taken into account during the soldering process.
This paper evaluates three processes for selective surface mount soldering. A Xenon Lamp-based heating system,a hot air heating system,and a reflow oven heating system are compared for use with both RoHS and non-RoHS compliant solders. Pull strengths of the solder connections,and intermetallic thicknesses of the connections are used to evaluate the solder connections.

Recently,with significant increasing of solder manufacturing cost due to raw materials,electronics makers are also faced with the same difficulty. And they are finding solutions that save cost by reducing the dross. This paper describes the implementation of a wave soldering system using inert gas. The system based on the PSA-generated nitrogen with residual oxygen levels of 100ppm has low maintenance cost and is very simple to retrofit. In this study,technical results and economic benefits are analyzed by feasibility and actual test. To analyze the effects of comparing nitrogen wave soldering with conventional air condition,we have evaluated the wettability of assemblies,dross and solder joint reliability. The inert wave soldering system shows significant dross reduction and its wettability is better than conventional. Also SEM analysis from solder joint shows good results.

The globalization of markets results in stronger competition with clearly noticeably cost pressure. For companies producing electronic equipment it is therefore of existential importance to reduce production costs whilst maintaining a consistently high quality level of the manufactured products. Manual repair soldering that is expensive,time-consuming and cost intensive is already unacceptable due to the required quality and the reproducibility of the whole manufacturing process.
In addition,densely populated multilayer boards and miniaturised,high-pin-count,fine-pitch devices cannot be efficiently repaired with high quality. "Hidden costs",such as productivity rates,operator training and damaged assembly costs have to be taken into consideration as well.
Special focus has to be set to lead-free applications as manual repair soldering processes can cause enormous thermal problems.
The target,therefore,has to be a zero-fault selective soldering process.
An appropriate printed circuit board design is of the utmost importance here. For example,the shape of the pads and their distance in relation to each other can benefit – or with the corresponding design – exclude the formation of bridges. The distance between a pad to be soldered and an adjoining one that is not to be wetted,also plays a role.
The distance between the individual pins,as well as the length of the pins,are likewise to be taken into account.
Moreover,by choosing the correct soldering nozzle,one can avoid the formation of soldering faults in the automatic selective soldering process.
The design of the soldering nozzle,as for example the shape or diameter,and the soldering nozzle technology used,such as wettable and non-wettable soldering nozzles,play a role here. Additional innovative features,such as debridging knives for example,can effectively avoid the formation of solder bridges,especially in the dip soldering process.
With many practical examples,this paper gives a detailed explanation of the individual points which should be found in the selective soldering process,with regard to the assembly design and solder nozzle technology.

Dross generation has always been a costly issue for the electronics assembly industry. At least half,and in many cases,more than half of the metal (solder) purchased for electronic manufacture is wasted as it becomes tied up in dross. With the advent of lead free solders as well as the spike in tin prices during 2008 the moderate economic pain of dross generation has become acute. In addition to metal cost,lead free solders have become known to exacerbate quality issues such as copper dissolution. A process introduced two years ago cures virtually all problems caused by dross and has now been shown in production to mitigate some of the other issues associated with lead free solders.
This paper will show the true cost of dross in 2008/2009 terms,including metal replacement,loss of efficiency,and safety as well as environmental and quality issues which clearly demonstrate a need for a solution to this problem. In addition to dross elimination the process has been shown in the lab to reduce temperatures for wave and selective soldering and to improve wetting. Updated full production data at major EMS assemblers as well as lab test data will be presented.
In addition to answering the technical questions,why and how the “economics of dross” will be examined and a specific and
significant cost savings scenario will be presented based on the first two years of full production.

The interaction of the drill entry material and the drill tool are critical to producing accurately aligned connections between the different layers in a printed circuit board. The trend towards miniaturization and increased complexity of printed circuits requires the use of micro and small diameter (< 0.3mm) to produce the hole for subsequent plating and circuit interconnection. These smaller tools must endure end-load and torque stresses that cause the bit to deflect resulting in hole mis-registration and/or drill breakage.
The amount of force is dependent on composition of the printed circuit as well as the processing parameters such as chipload and spindle rate. Phenolic and solid aluminum entry materials,used for printed circuit drilling since the 1980s,do not have the properties required to consistently produce a high quality,small diameter drilled hole. An engineered entry material,specifically designed for use with small drills,has been developed and is currently in worldwide use. This engineered entry ensures drill accuracy and minimizes drill deflection. These benefits can improve hole quality and registration and will allow further circuit miniaturization without compromising circuit integrity. Additionally,drill efficiencies benefit from improved drill wear,less breakage,and increased stack heights.
In this paper,data will be presented on the accuracy of holes produced by small and micro diameter drill tools utilizing this new engineered entry material compared to solid,composite,and lubricated entry materials. Hole registration accuracy will be analyzed and statistically compared using the industry standard centroid method. Currently available entry materials will be compared and contrasted. Benefits and recommendations for best processing practices of the engineered entry material will also be discussed.

The transition to lead-free solders has presented significant challenges for the electronics industry. One of the challenges is that typical lead-free soldering temperatures are much higher than those of tin-lead alloys. To maintain the reliability of printed circuit boards (PCBs) subsequent to higher assembly and rework requires new chemistries are required that give rise to materials with high glass transition (Tg) and high decomposition temperatures (Td). Increasing the crosslink density of a resin formulation is a common method used to achieve high Tg. Therefore,higher functionality resins and hardeners are being more commonly used. However,materials with high crosslink densities are also brittle. During the fabrication of PCBs holes are mechanically drilled into the laminate. Drilling of brittle laminates is problematic because of problems associated with cracking,delamination,and drill-bit wear and breakage. Although the drilling equipment,drill bits,and drilling
parameters can be optimized to minimize such issues,additional efforts are desirable to improve the drillability of the PCBs.
Toughening agents are being incorporated into the resin formulations to improve drillability.
This work reports results from the study of incorporating toughening agents into resin formulations and their effect on the toughness and drillability of electrical laminates. This work also reports on evaluation protocols that account for the high temperatures and strain rates that the laminates are subjected to during the drilling process. The objective of the work is to serve as a starting point in creating a toolbox that will help correlate the thermomechanical properties of the resin formulations to the drillability performance of the corresponding PCBs. These correlations can speed the new materials evaluation process relative to the drillability performance without the expensive and time-consuming process of performing extensive drilling studies.

As the requirements for controlled depth micro-vias become ever increasing in today’s market place the best feasible solution
appears to be laser drilling. However laser drilling can be problematic when approaching dielectric thicknesses over 3 mils. FR4 is a composite of epoxy and fiberglass with the fiberglass portion being most problematic for the laser. Since the fiberglass is a weave the laser will have to be adjusted to drill through the knuckle of the glass intersect and hit the capture pad. This is achievable however lateral ablation of the epoxy can occur. This phenomenon can lead to uneven plating and potential reliability issues as can be seen in Figure 1.