Technical Library | 2023-01-17 17:27:13.0
Reflow profile has significant impact on solder joint performance because it influences wetting and microstructure of the solder joint. The degree of wetting, the microstructure (in particular the intermetallic layer), and the inherent strength of the solder all factor into the reliability of the solder joint. This paper presents experimental results on the effect of reflow profile on both 63%Sn 37%Pb (SnPb) and 96.5%Sn 3.0%Ag 0.5%Cu (SAC 305) solder joint shear force. Specifically, the effect of the reflow peak temperature and time above solder liquidus temperature are studied. Nine reflow profiles for SAC 305 and nine reflow profiles for SnPb have been developed with three levels of peak temperature (230 o C, 240 o C, and 250 o C for SAC 305; and 195 o C, 205 o C, and 215 o C for SnPb) and three levels of time above solder liquidus temperature (30 sec., 60 sec., and 90 sec.). The shear force data of four different sizes of chip resistors (1206, 0805, 0603, and 0402) are compared across the different profiles. The shear force of the resistors is measured at time 0 (right after assembly). The fracture surfaces have been studied using a scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS)
Technical Library | 2019-10-21 09:58:50.0
An ACI Technologies customer inquired regarding printed circuit board(PCB) failures that were becoming increasingly prevalent after the SMT (surface mount technology) manufacturing process. The failures were detected by electrical testing, but were undetermined as to the location and specific devices causing the failures. The failures were suspected to be caused predominately in the BGA (ball grid array) devices located on specific sites on this 16 layer construction. Information that was provided on the nature of the failures (i.e., opens or shorts) included high resistance shorts that were occurring in those specified areas. The surface finish was a eutectic HASL (hot air solder leveling) and the solder paste used was a water soluble Sn/Pb(tin/lead).
Technical Library | 2014-07-02 16:46:09.0
Growth behaviors of intermetallic compounds (IMCs) and Kirkendall voids in Cu/Sn/Cu microbump were systematically investigated by an in-situ scanning electron microscope observation. Cu–Sn IMC total thickness increased linearly with the square root of the annealing time for 600 h at 150°C, which could be separated as first and second IMC growth steps. Our results showed that the growth behavior of the first void matched the growth behavior of second Cu6Sn5, and that the growth behavior of the second void matched that of the second Cu3Sn. It could be confirmed that double-layer Kirkendall voids growth kinetics were closely related to the Cu–Sn IMC growth mechanism in the Cu/Sn/Cu microbump, which could seriously deteriorate the mechanical and electrical reliabilities of the fine-pitch microbump systems
Technical Library | 2017-06-13 17:14:59.0
For tin-rich solder alloys, 200 C (392 F) is an extreme temperature. Intermetallic growth in tin-copper systems is known to occur and is believed to bear a direct relationship to failure mechanisms. This study of morphological changes with time at elevated temperatures was made to determine growth rates of tin-copper intermetallics. Preferred growth directions, rates of thickening, and notable changes in morphology were observed.Each of four tin-base alloys was flowed on copper and exposed to temperatures between 100 C and 200 C for time periods of up to 32 days. Metallographic sections were taken and the intermetallics were examined. Intermetallic layer thickening is characterized by several distinct stages. The initial growth of side plates is extremely rapid and exaggerated. This is followed by retrogression (spheroidization) of the elongated peaks and by general thick-
Technical Library | 2021-12-29 19:37:20.0
The purpose of this study was to compare the strength of the bond between resin and glass cloth for various composites (laminates) and its dependence on utilized soldering pad surface finishes. Moreover, the impact of surface finish application on the thermomechanical properties of the composites was evaluated. Three different laminates with various thermal endurances were included in the study. Soldering pads were covered with OSP and HASL surface finishes. The strength of the cohesion of the resin upper layer was examined utilizing a newly established method designed for pulling tests.
Technical Library | 2010-07-08 19:49:59.0
Aging characteristics of new lead free solder alloys are in question by many experts because of higher amount of tin’s effect on the diffusion of other metals, primarily copper, to create undesirable boundary intermetallics over long periods of time and even moderately elevated temperatures. A primary layer of intermetallics, Cu6Sn5 forms as the liquid solder makes contact with the solid copper substrate. This reaction however ceases as the solder temperature falls below that of liquidus. A secondary intermetallic Cu3Sn1, an undesirable weak and brittle layer, is thought to form over time and may be accelerated by even mildly elevated temperatures in electronic modules such as laptops under power. This project was designed to quantify the growth rate of Cu3Sn1 over an extended period of time in a thermal environment similar to a laptop in the power on mode.
Technical Library | 2019-06-20 00:09:49.0
It is well known that during service the layer of Cu6Sn5 intermetallic at the interface between the solder and a Cu substrate grows but the usual concern has been that if this layer gets too thick it will be the brittleness of this intermetallic that will compromise the reliability of the joint, particularly in impact loading. There is another level of concern when the Cu-rich Cu3Sn phase starts to develop at the Cu6Sn5/Cu interface and an imbalance in the diffusion of atomic species, Sn and Cu, across that interface results in the formation at the Cu3Sn/Cu interface of Kirkendall voids, which can also compromise reliability in impact loading. However, when, as is the case in some microelectronics, the copper substrate is thin in relation to the volume of solder in the joint an overriding concern is that all of the Cu will be consumed by reaction with Sn to form these intermetallics.This paper reports an investigation into the kinetics of the growth of the interfacial intermetallic, and the consequent reduction in the thickness of the Cu substrate in solder joints made with three alloys, Sn-3.0Ag-0.5Cu, Sn-0.7Cu-0.05Ni and Sn-1.5Bi-0.7Cu-0.05Ni.
Technical Library | 2007-03-08 19:31:10.0
Reflow profile has significant impact on solder joint performance because it influences wetting and microstructure of the solder joint. The degree of wetting, the microstructure (in particular the intermetallic layer), and the inherent strength of the solder all factor into the reliability of the solder joint. This paper presents experimental results on the effect of reflow profile on both 63%Sn 37%Pb (SnPb) and 96.5%Sn 3.0%Ag 0.5%Cu (SAC 305) solder joint shear force.
Technical Library | 2014-01-23 16:49:55.0
As reliability requirements increase, especially for defense and aerospace applications, the need to characterize components used in electronic assembly also increases. OEM and EMS companies look to perform characterizations as early as possible in the process to be able to limit quality related issues and improve both assembly yields and ultimate device reliability. In terms of BGA devices, higher stress conditions, RoHS compatible materials and increased package densities tend to cause premature failures in intermetallic layers. Therefore it is necessary to have a quantitative and qualitative test methodology to address these interfaces.
Technical Library | 2012-12-13 21:20:05.0
First published in the 2012 IPC APEX EXPO technical conference proceedings. We investigated the micro-void formation of solder joints after reliability tests such as preconditioning (precon) and thermal cycle (TC) by varying the thickness of Palladium (Pd) in Electroless Nickel / Electroless Palladium / Immersion Gold (ENEPIG) surface finish. We used lead-free solder of Sn-1.2Ag-0.5Cu-Ni (LF35). We found multiple micro-voids of less than 10 µm line up within or above the intermetallic compound (IMC) layer. The number of micro-voids increased with the palladium (Pd) layer thickness. Our results revealed that the micro-void formation should be related to (Pd, Ni)Sn4 phase resulted from thick Pd layer. We propose that micro-voids may form due to either entrapping of volatile gas by (Pd, Ni)Sn4 or creeping of (Pd, Ni)Sn4.
