Technical Library | 2019-06-11 09:36:13.0
An experiment was recently performed ACI Technologies for a customer that was interested in comparing the wetting of lead-free solders with varying temperature profiles and atmospheric conditions. In order to deliver an objective measurement of solder wetting (in addition to subjective inspection analysis), a simple wetting indicator pattern was added to the solder stencil in an area on the test vehicle that had exposed and unused copper.
Technical Library | 2019-06-04 10:19:46.0
Interconnection technology relies very heavily on the ability of the conductors on a printed wiring assembly to maintain reliable signal integrity. Harsh environmental factors can precipitate a loss of conductivity due to oxidation and corrosion. Connections are typically soldered or inserted using pressure fitted connectors to obtain enough surface contact to meet the electrical conductivity requirements. In pressure contacts, surface integrity is especially critical where the abrasive effects of retraction and insertion can wear off the metallic finish from the contact area. This can expose the underlying copper or nickel and lead to increased resistance at the contact points. These types of conductors are frequently found in card edge connectors where the terminations are plated with a layer of nickel and gold (frequently referred to as gold fingers). A hard gold is typically used containing very small amounts of nickel and cobalt to increase the wear resistance.
Technical Library | 2022-03-16 19:48:18.0
Dendrites, Electrochemical Migration (ECM) and parasitic leakage, are usually caused by process related contamination. For example, excess flux, poor handling, extraneous solder, fibers, to name a few. One does not normally relate these fails with environmental causes. However, creep corrosion is a mechanism by which electronic products fail in application, primarily related to sulfur pollution present in the air.1 The sulfur reacts with exposed silver, and to a lesser extent, exposed copper. This paper will explore various aspects of the creep corrosion chemical reaction
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 | 2021-11-03 16:52:47.0
This paper proposes the integration of pulsed photonic sintering into multi-material additive manufacturing processes in order to produce multifunctional components that would be nearly impossible to produce any other way. Pulsed photonic curing uses high power Xenon flash lamps to thermally fuse printed nanomaterials such as conductive metal inks. To determine the feasibility of the proposed integration, three different polymer additive manufacturing materials were exposed to typical flash curing conditions using a Novacentrix Pulseforge 3300 system. FTIR analysis revealed virtually no change in the polymer substrates, thus indicating that the curing energy did not damage the polymer. Next, copper traces were printed on the same substrate, dried, and photonically cured to establish the feasibility of thermally fusing copper metal on the polymer additive manufacturing substrates. Although drying defects were observed, electrical resistivity values ranging from 0.081 to 0.103 Ω/sq. indicated that high temperature and easily oxidized metals can be successfully printed and cured on several commonly used polymer additive manufacturing materials. These results indicate that pulsed photonic curing holds tremendous promise as an enabling technology for next generation multimaterial additive manufacturing processes.
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 | 2021-11-03 17:05:39.0
Additively printed circuits provide advantages in reduced waste, rapid prototyping, and versatile flexible substrate choices relative to conventional circuit printing. Copper (Cu) based inks along with intense pulsed light (IPL) sintering can be used in additive circuit printing. However, IPL sintered Cu typically suffer from poor solderability due to high roughness and porosity. To address this, hybrid Cu ink which consists of Cu precursor/nanoparticle was formulated to seed Cu species and fill voids in the sintered structure. Nickel (Ni) electroplating was utilized to further improve surface solderability. Simulations were performed at various electroplating conditions and Cu cathode surface roughness using the multi-physics finite element method. By utilizing a mask during IPL sintering, conductivity was induced in exposed regions; this was utilized to achieve selective Ni-electroplating. Surface morphology and cross section analysis of the electrodes were observed through scanning electron microscopy and a 3D optical profilometer. Energy dispersive X-ray spectroscopy analysis was conducted to investigate changes in surface compositions. ASTM D3359 adhesion testing was performed to examine the adhesion between the electrode and substrate. Solder-electrode shear tests were investigated with a tensile tester to observe the shear strength between solder and electrodes. By utilizing Cu precursors and novel multifaceted approach of IPL sintering, a robust and solderable Ni electroplated conductive Cu printed electrode was achieved.
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