Technical Library | 2021-12-29 19:52:50.0
Medtronic seeks to quantify the thermal aging limits of electroless Ni-electroless Pd-immersion Au (ENEPIG) surface finishes to determine how aggressive the silicon burn-in process can be without loss of solderability. Silicon burn-in (power testing at elevated temperature) is used to eliminate early field failures, critical for device reliability. Thermal aging due to burn-in or annealing causes Ni and Pd diffusion to and oxidation on the surface. Surface oxides limit wetting of the PbSn solder, affecting electrical connectivity of components soldered afterburn-in. Isothermal aging of two ENEPIG surface finishes was performed at 75°C-150°C for 100 hrs-1500hrs to test the thermal aging limits and identify how loss of solderability occurs.
Technical Library | 2013-02-14 12:54:29.0
Boundary-scan (1149.1) technology was originally developed to provide a far easier method to perform digital DC testing to detect intra-IC interconnect assembly faults, such as solder shorts and opens. Today's advanced IC technology now includes high-speed differential interfaces that include AC or DC coupling components loaded on the printed circuit assembly. Simple stuck-at-high/low test methods are not sufficient to detect all assembly fault conditions, which includes shorts, opens and missing components. Improved diagnostics requires detailed circuit analysis, predictive assembly fault simulation and more complex testing to isolate and accurately detect all possible assembly faults... First published in the 2012 IPC APEX EXPO technical conference proceedings
Technical Library | 2017-11-03 13:39:06.0
If someone were to ask what the most important part of their favorite electronic device is, they are likely to point to the printed circuit board (PCB) responsible for making the device work before moving on to other components. From large motherboards to tiny chips, most of the technology that retail consumers take for granted comes down to a properly installed and calibrated PCB.
Technical Library | 2010-05-06 18:46:29.0
Stencil printing technology has come a long way since the early 80’s when SMT process gained importance in the electronics packaging industry. In those early days, components were fairly large, making the board design and printing process relatively simple. The current trend in product miniaturization has led to smaller and more complex board designs. This has resulted into designs with maximum area utilization of the board space. It is not uncommon, especially for hand held devices, to find components only a few millimeters from the edge of the board. The board clamping systems used in the printing process have become a significant area of concern based on the current board design trend.
Technical Library | 2020-11-24 23:01:04.0
The miniaturization trend is driving industry to adopting low standoff components or components in cavity. The cost reduction pressure is pushing telecommunication industry to combine assembly of components and electromagnetic shield in one single reflow process. As a result, the flux outgassing/drying is getting very difficult for devices due to poor venting channel. This resulted in insufficiently dried/burnt-off flux residue. For a properly formulated flux, the remaining flux activity posed no issue in a dried flux residue for no-clean process. However, when venting channel is blocked, not only solvents remain, but also activators could not be burnt off. The presence of solvents allows mobility of active ingredients and the associated corrosion, thus poses a major threat to the reliability. In this work, a new halogen-free no-clean SnAgCu solder paste, 33-76-1, has been developed. This solder paste exhibited SIR value above the IPC spec 100 MΩ without any dendrite formation, even with a wet flux residue on the comb pattern. The wet flux residue was caused by covering the comb pattern with 10 mm × 10 mm glass slide during reflow and SIR testing in order to mimic the poorly vented low standoff components. The paste 33-76-1 also showed very good SMT assembly performance, including voiding of QFN and HIP resistance. The wetting ability of paste 33-76-1 was very good under nitrogen. For air reflow, 33-76-1 still matched paste C which is widely accepted by industry for air reflow process. The above good performance on both non-corrosivity with wet flux residue and robust SMT process can only be accomplished through a breakthrough in flux technology.
Technical Library | 2020-10-27 02:07:31.0
For companies that choose to take the Pb-free exemption under the European Union's RoHS Directive and continue to manufacture tin-lead (Sn-Pb) electronic products, there is a growing concern about the lack of Sn-Pb ball grid array (BGA) components. Many companies are compelled to use the Pb-free Sn-Ag-Cu (SAC) BGA components in a Sn-Pb process, for which the assembly process and solder joint reliability have not yet been fully characterized. A careful experimental investigation was undertaken to evaluate the reliability of solder joints of SAC BGA components formed using Sn-Pb solder paste. This evaluation specifically looked at the impact of package size, solder ball volume, printed circuit board (PCB) surface finish, time above liquidus and peak temperature on reliability. Four different BGA package sizes (ranging from 8 to 45 mm2) were selected with ball-to-ball pitch size ranging from 0.5mm to 1.27mm. Two different PCB finishes were used: electroless nickel immersion gold (ENIG) and organic solderability preservative (OSP) on copper. Four different profiles were developed with the maximum peak temperatures of 210oC and 215oC and time above liquidus ranging from 60 to 120 seconds using Sn-Pb paste. One profile was generated for a lead-free control. A total of 60 boards were assembled. Some of the boards were subjected to an as assembled analysis while others were subjected to an accelerated thermal cycling (ATC) test in the temperature range of -40oC to 125oC for a maximum of 3500 cycles in accordance with IPC 9701A standard. Weibull plots were created and failure analysis performed. Analysis of as-assembled solder joints revealed that for a time above liquidus of 120 seconds and below, the degree of mixing between the BGA SAC ball alloy and the Sn-Pb solder paste was less than 100 percent for packages with a ball pitch of 0.8mm or greater. Depending on package size, the peak reflow temperature was observed to have a significant impact on the solder joint microstructural homogeneity. The influence of reflow process parameters on solder joint reliability was clearly manifested in the Weibull plots. This paper provides a discussion of the impact of various profiles' characteristics on the extent of mixing between SAC and Sn-Pb solder alloys and the associated thermal cyclic fatigue performance.
Technical Library | 2022-10-31 17:30:40.0
This paper presents a quantitative analysis of solder joint reliability data for lead-free Sn-Ag-Cu (SAC) and mixed assembly (SnPb + SAC) circuit boards based on an extensive, but non-exhaustive, collection of thermal cycling test results. The assembled database covers life test results under multiple test conditions and for a variety of components: conventional SMT (LCCCs, resistors), Ball Grid Arrays, Chip Scale Packages (CSPs), wafer-level CSPs, and flip-chip assemblies with and without underfill. First-order life correlations are developed for SAC assemblies under thermal cycling conditions. The results of this analysis are put in perspective with the correlation of life test results for SnPb control assemblies. Fatigue life correlations show different slopes for SAC versus SnPb assemblies, suggesting opposite reliability trends under low or high stress conditions. The paper also presents an analysis of the effect of Pb contamination and board finish on lead-free solder joint reliability. Last, test data are presented to compare the life of mixed solder assemblies to that of standard SnPb assemblies for a wide variety of area-array components. The trend analysis compares the life of area-array assemblies with: 1) SAC balls and SAC or SnPb paste; 2) SnPb balls assembled with SAC or SnPb paste.
Technical Library | 2016-07-28 17:00:20.0
Packaging trends enable disruptive technologies. The miniaturization of components reduces the distance between conductive paths. Cleanliness of electronic hardware based on the service exposure of electrical equipment and controls can improve the reliability and cost effectiveness of the entire system. Problems resulting from leakage currents and electrochemical migration lead to unintended power disruption and intermittent performance problems due to corrosion issues.Solvent cleaning has a long history of use for cleaning electronic hardware. Limitations with solvent based cleaning agents due to environmental effects and the ability to clean new flux designs commonly used to join miniaturized components has limited the use of solvent cleaning processes for cleaning electronic hardware. To address these limitations, new solvent cleaning agents and processes have been designed to clean highly dense electronic hardware.The research study will evaluate the cleaning and electrical performance using the IPC B-52 Test Vehicle. Lead Free noclean solder paste will be used to join the components to the test vehicle. Ion Chromatography and SIR values will be reported.
Technical Library | 2023-01-02 17:50:34.0
Silver bearing alloys have been used in electronics soldering for many years. Silver has been used in tin-lead solders (Sn62Pb36Ag2) to combat silver scavenging from silver plated electronic components as well as to improve thermal fatigue resistance. Many of the common lead-free alloys contain some amount of silver. Silver bearing alloys have good electrical and thermal conductivity as well as the ability to wet to the common surface finishes used in printed wiring assemblies, thus giving it all the attributes needed for an electronic solder alloy. Presence of silver in Sn based solders increases the bulk solder modulus and is generally believed to improve resistance to fatigue from thermal cycles. Increased solder modulus can be advantageous or disadvantageous depending on the desired performance attribute. For example in high strain rate situations, higher modulus of the bulk solders results in lower life time. A wide variety of leaded and lead-free
Technical Library | 2014-10-30 01:48:43.0
The ultimate life of a microelectronics component is often limited by failure of a solder joint due to crack growth through the laminate under a contact pad (cratering), through the intermetallic bond to the pad, or through the solder itself. Whatever the failure mode proper assessments or even relative comparisons of life in service are not possible based on accelerated testing with fixed amplitudes, or random vibration testing, alone. Effects of thermal cycling enhanced precipitate coarsening on the deformation properties can be accounted for by microstructurally adaptive constitutive relations, but separate effects on the rate of recrystallization lead to a break-down in common damage accumulation laws such as Miner's rule. Isothermal cycling of individual solder joints revealed additional effects of amplitude variations on the deformation properties that cannot currently be accounted for directly. We propose a practical modification to Miner's rule for solder failure to circumvent this problem. Testing of individual solder pads, eliminating effects of the solder properties, still showed variations in cycling amplitude to systematically reduce subsequent acceleration factors for solder pad cratering. General trends, anticipated consequences and remaining research needs are discussed
