A Control-Chart Based Method for Solder Joint Crack Detection

Many researchers have used different failure criteria in published solder joint reliability studies. Since the reported timeto-failure would be different if different failure criteria were used, it would be difficult to compare the reported reliability life of solder joints from one study to another. The purpose of this study is to evaluate the effect of failure criteria on the reported thermal fatigue life and determine which failure criterion could detect failure sooner. First, the application of the control-chart-based method in a thermal cycling reliability study is described. The reported time-to-failure data were then compared based on four different failure criteria: a control-chart-based method, a 20% resistance increase from IPC-9701A, a resistance threshold of 500 V, and an infinite resistance. Over 3.5 GB resistance data measured by data loggers from a low-silver solder joint reliability study were analyzed. The results show that estimated time-to-failure based on the control-chart-based method is very similar to that when the IPC-9701A failure criterion is used. Both methods detected failure much earlier than the failure criterion of a resistance threshold of 500 V or an infinite resistance. A scientific explanation is made of why the 20% increase in IPC-9701A is a reasonable failure criterion and why the IPC-9701A and the control-chart-based method produced similar results. Three different stages in resistance change were identified: stable, crack, and open. The duration of the crack stage depends on the severity of the test conditions. It is recommend the control-chart-based method be used as the failure criterion because it not only monitors the average of resistance, but also monitors the dispersion of resistance in each thermal cycle over time

Estimation of Liquidus Temperature when SnAgCu BGA/CSP Components are Soldered with SnPb Paste

Recently, the soldering of lead-free components with SnPb paste, or lead-free backward compatibility, is becoming a hot topic. One of the major challenges in backward compatibility assembly is the development of a right reflow profile for the soldering of SnAgCu Ball Grid Array (BGA)/Chip Scale Package (CSP) components with SnPb paste. If the SnAgCu reflow profile is used, the reflow temperature may be too high for other SnPb components in the same board during assembly according to the component rating per IPC/JEDEC J-STD-020C. In addition, the flux in SnPb solder paste may not function properly in such a high reflow temperature. On the other hand, if the SnPb reflow profile is used, SnAgCu solder ball may only partially melt. The incomplete mixing of the solder paste with the BGA/CSP ball raises serious reliability concern. Therefore, it is important to know the minimum reflow peak temperature that is able to achieve complete mixing of SnPb paste with leadfree components. This paper presents a method to estimate the liquidus temperature of mixed compositions when SnAgCu BGA/CSP components are soldered with SnPb paste. The liquidus temperature is the minimum reflow peak temperature able to achieve complete mixing of SnPb paste with lead-free components. It will be shown that the liquidus temperature depends on the Pb ratio in the mixed composition and the liquidus temperature is below 217°C, which is the liquidus temperature of SnAg3.OCuO.5 solder. The liquidus temperatures of several experimental studies in literature are estimated and it is found that the estimated temperatures are consistent with experimental results. A user interface is designed using Visual Basic for Application in the Microsoft Excel environment to facilitate the estimation of the liquidus temperature. It is expected that the estimation of the mixed compositions liquidus temperature will be able to guide process engineers to develop a right reflow profile in backward compatibility assembly

A Control-Chart Based Method for Solder Joint Crack Detection - conference proceeding

Many researchers have used different failure criteria in the published solder joint reliability studies. Since the reported time-to-failure would be different if different failure criteria were used, it would be difficult to compare the reported reliability life of solder joints from one study to another. The purpose of this study is to evaluate the effect of failure criteria on the reported thermal fatigue life and find out which failure criterion can detect failure sooner. First, the application of the control-chart based method in a thermal cycling reliability study is described. The reported time-to-failure data were then compared based on four different failure criteria: a control-chart based method, a 20% resistance increase from IPC-9701A, a resistance threshold of 500Ω, and an infinite resistance. Over 3.5 GB resistance data measured by data loggers from a low-silver solder joint reliability study were analyzed. The results show that estimated time-to-failure based on the control-chart method is very similar to that when the IPC-9701A failure criterion is used. Both methods detected failure much earlier than the failure criterion of a resistance threshold of 500Ω or an infinite resistance. A scientific explanation is made of why the 20% increase in IPC-9701A is a reasonable failure criterion and why the IPC-9701A and the control-chart based method produced similar results. Three different stages in resistance change were identified: stable, crack, and open. It is recommended that the control-chart based method be used as failure criterion because it not only monitors the average of resistance, but also monitors the dispersion of resistance in each thermal cycle over time

Wire Bonding Challenges in Optoelectronics Packaging

Wire bonding has been used in integrated circuit (IC) packaging for many years. However, there are many challenges in wire bonding for optoelectronics packaging. These challenges include bonding on sensitive devices, bonding over cavity, bonding over cantilevel leads and bonding temperature limitations. The optoelectronics package design brings another challenge, which requires wire bonding to have deep access capability. In this paper, the wire bonding technologies are reviewed and ball bonding and wedge bonding are compared. The variables that affect the wire bonding process are then discussed. Finally, the challenges of wire bonding in optoelectronics packaging are presented in detail

A Study of Solder Joint Failure Criteria

One of the challenges in an experimental study of solder joint reliability is to determine when cracks occur in a solder joint or when a solder joint fails. Cracks in a real solder joint are difficult to identify using an X-Ray system. Cross-sectioning and scanning electron microscopy (SEM) is a destructive method. A common non-destructive test method is to monitor resistance increase in a solder joint or a daisy-chain. However, no scientific research has been done in establishing the relationship between the crack area of an interconnection and the change in resistance of the interconnection. This paper proposes a method of defining failure criteria as the resistance increase in a solder joint exceeding a threshold. The threshold is determined by k times the range over the natural variation in resistance measured by a measurement system. The natural variation by random cause is judged using X-bar and R charts. The principles of defining failure criteria are to be able to detect failure of solder joints as early as possible with minimum false detection due of measurement system error/variation. An experimental study confirmed that a full crack of an interconnection occurs when the increase of resistance in the interconnection is 10 times the natural variation of resistance change. The results of this study could be used to narrow the definition of failure in consensus standards IPC 9701A, JESD22-B111, and IPC/JEDEC-9702

Designing and Manufacturing Microelectronic Packages for High-Power Light-Emitting Diodes

A new microelectronic package was designed for a high-power light-emitting diode (LED). The objective was to build a package that enables the LED to operate with currents as high as 2 Amps. An innovative thin-film interface has been developed to electrically connect the cathode of the LED die to a 22AWG Cu wire. This thin-film interface is wirebondable and solderable, and consists of three layers: Au, Ni93/V7, and Si. Four 1 mil Au wirebonds, supporting 2A of maximum current, connect the Au thin-film to the LED die cathode. Sn96Ag4 solder is used for connecting the Ni93/V7 thin-film to the 22AWG Cu wire. To provide an electrical, mechanical and thermal platform for the anode of the LED die, a sub-assembly was developed. This sub-assembly utilizes a Cu substrate on which the anode of the LED die is attached with Au80Sn20 solder. The LED die, thin-film interface and Cu substrate integrate into the sub-assembly, which then solders onto a Cu heatsink. Electrical current flows into the heatsink, through the LED, across the thin-film interface, then out the Cu wire. All-metal interfaces from the LED anode to the heatsink provide a thermally conductive path. However, testing results show that the LED fails with currents of 815 mAmps or less. It appears that the failure was caused by thermal management within the die and is not due to the design of the package

Finding and Optimising the Key Factors for the Multiple-Response Manufacturing Process

With the advent of modern technology, manufacturing processes became so sophisticated that a single quality characteristic cannot reflect the true product quality. Thus, it is essential to perform the key factor analysis for the manufacturing process with multiple-input (factors) and multiple-output (responses). In this paper, an integrated approach of using the desirability function in conjunction with the Mahalanobis-Taguchi-Gram Schmit (MTGS) system is proposed in order to find and optimise the key factors for a multiple-response manufacturing process. The aim of using the MTGS method is to standardise and orthogonalise the multiple responses so that the Mahalanobis distance for each run can be calculated and the multi-normal assumption for the correlated responses can be relaxed. A realistic example of the solder paste stencil printing process is then used to demonstrate the usefulness of our proposed approach in a practical application

Uncertainty Modulates the Effect of Transcranial Stimulation Over the Right Dorsolateral Prefrontal Cortex on Decision-Making Under Threat

Threat is a strategy that can be used to impact decision-making processes in bargaining. Abundant evidence suggests that credible threat and incredible threat both influence the obeisance of others. However, it is not clear whether the decision-making processes under credible threat and incredible threat during bargaining involve differential neurocognitive mechanisms. Here, we employed cathodal transcranial direct current stimulation (tDCS) to deactivate the right dorsolateral prefrontal cortex (rDLPFC) to address this question while subjects allocated and reported the subjective probability of future rejection under incredible threat and credible threat. We found that application of cathodal tDCS over the rDLPFC decreased the proposer’s subjective inference of probability of rejection and the offer to the responder under incredible threat. Conversely, the same stimulation did not lead to a significant difference compared to the sham group in subjective probability and offer under credible threat. These results suggested that decision-making processes under the two types of threat during bargaining were associated with different neurocognitive substrates, because the punishment for non-compliance was uncertain under incredible threat, whereas it was certain under credible threat. We decreased activity in the rDLPFC, which is involved in decision-making processes related to bargaining under incredible threats, and observed significantly impacted behavior. The differential neurocognitive bases of subjective probability of rejection under incredible threat and credible threat resulted in different tDCS effects

Backward and Forward Compatibility

In response to the European Union (EU) Restriction of Hazardous Substances (RoHS) and other countries’ impending lead-free directives, the electronics industry is moving toward lead-free soldering. Total lead-free soldering requires not only lead-free solder paste but also lead-free printed circuit board (PCB) finish and lead-free component/packages. Transitioning tin-lead (SnPb) soldering to totally lead-free soldering is a complex issue and involves movement of the whole electronics industry supply chain. In reality, there is a transition period

Neural Dynamics of Processing Probability Weight and Monetary Magnitude in the Evaluation of a Risky Reward

Risky decision-making involves risky reward valuation, choice, and feedback processes. However, the temporal dynamics of risky reward processing are not well understood. Using event-related brain potential, we investigated the neural correlates of probability weight and money magnitude in the evaluation of a risky reward. In this study, each risky choice consisted of two risky options, which were presented serially to separate decision-making and option evaluation processes. The early P200 component reflected the process of probability weight, not money magnitude. The medial frontal negativity (MFN) reflected both probability weight and money magnitude processes. The late positive potential (LPP) only reflected the process of probability weight. These results demonstrate distinct temporal dynamics for probability weight and money magnitude processes when evaluating a risky outcome, providing a better understanding of the possible mechanism underlying risky reward processing