Technical Library | 2023-01-17 17:22:28.0
The impact of voiding on the solder joint integrity of ball grid arrays (BGAs)/chip scale packages (CSPs) can be a topic of lengthy and energetic discussion. Detailed industry investigations have shown that voids have little effect on solder joint integrity unless they fall into specific location/geometry configurations. These investigations have focused on thermal cycle testing at 0°C-100°C, which is typically used to evaluate commercial electronic products. This paper documents an investigation to determine the impact of voids in BGA and CSP components using thermal cycle testing (-55°C to +125°C) in accordance with the IPC- 9701 specification for tin/lead solder alloys. This temperature range is more typical of military and other high performance product use environments. A proposed BGA void requirement revision for the IPC-JSTD-001 specification will be extracted from the results analysis.
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 | 2015-01-05 17:38:26.0
The impact of voiding on the solder joint integrity of ball grid arrays (BGAs)/chip scale packages (CSPs) can be a topic of lengthy and energetic discussion. Detailed industry investigations have shown that voids have little effect on solder joint integrity unless they fall into specific location/geometry configurations. These investigations have focused on thermal cycle testing at 0°C-100°C, which is typically used to evaluate commercial electronic products. This paper documents an investigation to determine the impact of voids in BGA and CSP components using thermal cycle testing (-55°C to +125°C) in accordance with the IPC-9701 specification for tin/lead solder alloys. This temperature range is more typical of military and other high performance product use environments. A proposed BGA void requirement revision for the IPC-JSTD-001 specification will be extracted from the results analysis.
Technical Library | 2013-02-28 17:14:36.0
While it has long been known that the Cu6Sn5 intermetallic that plays a critical role in the reliability of solder joints made with tin-containing alloys on copper substrates exists in two different crystal forms over the temperature range to which electronics circuitry is exposed during assembly and service, it has only recently been recognized that the change from one form to the other has implications for solder joint reliability. (..) In this paper the authors report a study of the effect of cooling rates on Cu6Sn5 crystals. Cooling rates from 200°C ranged from 10°C/minute to 100°C/minute and the effect of isothermal ageing at intermediate temperatures was also studied. The extent of the phase transformation after each regime was determined using synchrotron X-ray diffraction. The findings have important implications for the manufacture of solder joints and their in-service performance... First published in the 2012 IPC APEX EXPO technical conference proceedings....
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.
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