This paper presents lead-free ball grid array (BGA) packages subjected to two ball removal and two ball attachment techniques. Solder attach strength is used as a metric to examine the reballing process. The impact of isothermal aging is also examined. In this study,lead-free (SAC305) 676 IO and 256 IO BGAs were reballed with eutectic tin-lead solder spheres. Two solder ball removal processes and two ball re-attachment processes were examined. For the 676 IO BGAs,the solder wick and low temperature solder wave removal process were examined. Ball re-attachment for this part was conducted with the perform method. For the 256 IO BGA,the low temperature solder wave removal process was applied followed by either perform or ball drop re-attach methods. Ball shear and the cold bump test results do not show a correlation with the reballing process. Further,isothermal aging does not appear to greatly influence the interconnect strength of tin-lead solder. Non-reballed lead-free solder balls were found to have greater strength and a wider strength distribution as compared to the reballed tin-lead solder samples. For the cold bump test,an increase in pull speed correlated to an increase in solder pull strength.

The recent use of lead free alloys has made the wave solder process more challenging in terms of achieving acceptable solder joints for both SMT and PTH components. It has been found that the Design for Manufacturability (DFM) guidelines,which were established for tin lead processes,in many cases do not result in the same level of quality joints when soldering with lead free alloy. Therefore,in order to improve the process yields and reduce manufacturing costs when converting to lead free,it is essential to establish DFM guidelines specifically for lead free soldering. The effect of pin to hole ratio,quantity of large copper planes connected to a pin through hole barrel,connection types for PTH and land patterns for glue and wave chip components are some of the main features which require further investigation for design optimization.
As there are a variety of lead free alloys available on the market today,each with differing properties,it is also important to determine if a set of DFM guidelines result in similar results among these various alloys.
This paper will discuss the outcome of a study of several DFM features incorporated on an internally designed test vehicle,which was created to evaluate alternative lead free alloys for Celestica. The DFM features included land pattern design and varying component spacing for chip components,pin to hole ratio and its interaction with the quantity of large copper planes connected to a PTH,quantity of large copper planes connected to a PTH and its interaction with the type of connection either solid or four spokes. The test vehicle was assembled with four Pb-free alloys (Sn-Cu-Ni,Sn-Ag-Cu-Bi,Sn-Cu-X & SAC405) and 63Sn-37Pb alloy as a baseline. The quality level of each of the described DFM features will be discussed. In addition to this,a detailed barrel fill analysis for the PTH components will be shown.

Over 3 years ago,Zestron initially addressed cleaning underneath 4 MIL standoff components. With the emergence of lead-free and even smaller components new challenges have now arisen to include components with less than 1MIL gaps.
This study set out to specifically investigate the impact of mechanical vs. chemical contributions during the removal of contamination under 1-2 MIL standoff components,respectively. To validate the results obtained,extensive studies were conducted,including actual user case-studies,specifically prepared test-assemblies,iterative experimentation,as well as new mechanical innovations that might help customers in future. The latter include but are not limited to various flow patterns as well as industry leading cleaning agents. As a result the authors will also include experimental data to address fluid flow mechanics,temperature and concentration related effects.
Initial results obtained indicate that clean-ability of residues under low standoff components has become a non-trivial issue. Not only are residues becoming harder to remove,but at the same token the penetration of the cleaning agent seems to be in direct relationship with the geometry and height of the components used. We will also illustrate surprising and unexpected results. For example,under specific conditions cleaning results under 1-2 MIL standoffs provided better cleanliness than under 4-5MIL standoffs!

Electronics,especially mobile electronic items,are subjected to unintentional abuse by having various beverages spilled onto or into them. Ion Chromatography and emission spectroscopy were used to identify the common inorganic ions in various carbonated drinks,coffee,tea,milk,juices,beer,wine,hot chocolate and a well-known sports drink. Except for the carbonated drinks,the others were then intentionally spilled onto clean circuit boards,dried,extracted and re-analyzed. The results show that there is generally little change from the virgin materials using the IPC extraction method and thus a library of “usual suspects” can be accumulated for comparison purposes for electronic products that come back from the field.

An assessment to measure the cleanliness of the area underneath a component has been completed. The assessment uses an 8”×9”×0.093” test vehicle with FR4 laminate,OSP surface finishing,and 21 package types. The test vehicles went through a Pubs assembly process and inline aqueous cleaning. The two test methodologies used are Ion Chromatography (IC) and Electron Migration (EM). Based on the test results,most of components pass the criteria,except three high pin count LBGA’s on Bromide level of Paste B. No significant differences between the low stand-off components group and other groups. Among the four low stand-off components,LGA133,which has the lowest stand-off,shows a higher Total Anion level. The test results also verified that,within the similar package types,the ionic level is likely proportional to the stencil paste volume. It also shows there is no statistical differences among the three Time-To-Wash cases. In other words,if the board is washed within 72 hours,there is no significant difference on ionic level. EM test results are still under analysis. It will be available at conference.

Addition of Al into SAC alloys reduces the number of hard Ag3Sn and Cu6Sn5 IMC particles,and forms larger,softer non-stoichiometric AlAg and AlCu particles. This results in a significant reduction in yield strength,and also causes some moderate increase in creep rate. For high Ag SAC alloys,adding Al 0.1-0.6% to SAC alloys is most effective in softening,and brings the yield strength down to the level of SAC105 and SAC1505,while the creep rate is still maintained at SAC305 level. Addition of Ni results in formation of large (Ni,Cu)3Sn4 IMC particles and loss of Cu6Sn5 particles. This also causes softening of SAC alloys,although to a less extent than that of Al addition. Addition of Al also drives the microstructure to shift from near-ternary SnAgCu eutectic toward combination of eutectic SnAg and eutectic SnCu. Addition of Ni drives shifting toward eutectic SnAg. For SAC+Al+Ni alloys,the pasty range and liquidus temperature are about 4?C less than that of SAC105 or SAC1505 if the addition quantity is less than about 0.6%. Addition of Al and Ni also results in a slight decrease in modulus and elongation at break,although the tensile strength is not affected.

It is known that pure tin will undergo an allotropic transformation below 13°C where it becomes a semiconductor with a 26% volume increase,and in appearance turns from a bright shiny metallic material,white ß tin,to a dark blue/grey dust,a tin. Such a transformation for an electrical interconnect is disastrous,if it were to occur in any of the high tin lead-free alloys it would be a catastrophe. The elimination of lead,one of the best elements to arrest the transformation process,has resulted in a number of high tin content alloys about which the potential to transform is unknown. Environmental factors that may enhance or arrest the rate and the incubation period of the transformation processes are also unknown.
An analysis based on the lattice parameter of a tin to find similar materials was substantiated and was used to select inoculators to minimize the incubation period. Following which a number of experiments were conducted using CdTe. To further the study the transformation process was videoed using time lapse photography with the sample held at –35°C in vacuum system. The transformation progressed radically from the inoculation point,starting at the surface. Propagation into the bulk occurred by peeling; with the external layers tending to “roll out” due to the volume expansion of the internal layers. In the meantime,cracks parallel to the propagation direction formed. Typically a sample would completely transform in just over 24 hours.
Further work is now looking at the effect of cubic ice,temperature on the transformation and the effect of alloying additions in influencing the transformation process.
The roll of this particular lattice form of ice is a worrying aspect,since it can commonly occur under the relevant temperatures. Experiments have shown that ice can act as the inoculators,seeding the transformation,particularly when other inoculators are in the vicinity.

Flux technology for lead-free alloys differs considerably from that for eutectic Sn/Pb solder systems,mainly for soldering and cleaning purpose. For most of the lead-free solders,paste handling is not an issue. Although dust has not settled yet,it becomes clear that the flux needed should have higher flux capacity,higher oxygen barrier capability,and higher thermal stability. Halide-free fluxes are placing greater challenge on cleaning due to the lower flux efficiency per unit flux volume than halide-containing fluxes. The oxygen barrier capability can be reduced if inert reflow atmosphere is available. RMA flux,no-clean flux with high solid content,and water washable systems exhibit a greater prospect to be upgraded for lead-free applications. For 58Bi/42Sn solder,flux with low activation temperature is needed. For Sn/Zn/Bi solders,the demand on flux capacity and oxygen barrier capability is even greater than other lead-free solder systems. In addition,the fluxes should be stable enough to retard the reaction with Zn. Cleaning flux residue of lead-free solder pastes is more challenging than that of Sn/Pb systems. This is primarily due to (1) higher reflow temperature,(2) higher flux capacity,therefore higher flux-induced side reactions,(3) more tin-salts formation. The cleanability decreases from no-clean soft-residue fluxes to water washable fluxes to no-clean hard residue fluxes. Improvement in cleanability may link to improvement in thermal stability of fluxes. Semi-aqueous and/or aqueous solvent sprayable cleaners yield the best cleaning efficiency,if the solvent is selected properly. Spray is the most critical mechanical agitation,regardless whether it is spray-in-air or spray-under-immersion. Ultrasonic aid also imparted a significant positive effect. Saponified aqueous spray is one of the top choices for cleaning water washable residues. Better solvency and spray are the directions for further improving cleaning. Improvement in flux thermal stability will help both soldering and cleaning.

Companies seeking sales or suppliers in the global marketplace must proceed with caution. This presentation provides an overview of U.S. regulation of import and export transactions. Importers must exercise “reasonable care” to ensure that accurate information is provided to U.S. Customs & Border Protection regarding the nature,value,and origin of imported merchandise. Reliance on third parties or suppliers for that information does not protect the importer from liability. Further,importers must establish and maintain compliance programs consistent with the customs laws and regulations. On the export side,companies seeking new markets for their products must ensure compliance with U.S. export controls,economic sanctions,and embargoes. This presentation will give companies insight into how to manage these risks while employing legal tools to reduce costs in international trade.

•Rewards businesses with a dollar for dollar reduction of tax
•Rewards “evolutionary” and “revolutionary” activities
•Federal tax benefit can be as high as 6.5% of investment in new products and processes
•Ability to file retroactively