Jan Urbanek

Surface tension measurement of the solders by non-wetting specimen

The knowledge of actual value of surface tension is important for the understanding to several soldering aspects, such as wetting, joint shape, fluxing action and, particularly, for the quantification of solderability testing. High surface tension is required for wave soldering. This article deals with the surface tension measurement of the lead and lead-free solders. For our measurement we used one of the solderability evaluation methods known as the wetting balance method, which is used to measure wetting force. A wetting balance has been used for evaluation of solderability. This method is based on the measurement of the wetting force. We used a special technique to obtain the surface tension values of the measured solders. The measurement was carried out on the ninth different types of solders (lead and lead free) and on non-wetting measurement specimen (teflon, nonstick cylinder).

Influence of the reduced oxygen concentration on the wetting force

The knowledge of actual value of surface tension is important for the understanding to several soldering aspects, such as wetting, joint shape, fluxing action and, particularly, for the quantification of solderability testing. High surface tension is required for wave soldering.Values of surface tension are mainly caused by measurement conditions (temperature, ambient -air, inert atmosphere of the different composition etc.). We have measured influence of the reduced oxygen concentration on the wetting force. The change of the wetting force is related to the change of the surface tension. We used a wetting balance technique to measure the wetting force change which depends on the changing oxygen concentration. The measurement was carried out on two different types of solders (Sn63Pb37 and Sn95,5Ag3,8Cu0,7) and on non-wetting measurement specimen (teflo-non-stick cylinder).

Shear strength of joints made of lead-free solders

This paper presents results of mechanical testing of soldered joints made of widely used lead free solder and most popular lead containing one. Measured parameter is shear strength. Tested solders were lead-free Sn-3,8Ag-0,7Cu and lead containing Sn-37Pb. With those solders set of SMD resistors was mounted on pads made of copper and copper electrolytic covered with nickel layer. As mechanical ruggedness of soldered joint strongly depends on presence of intermetallics compounds samples were treated to heat 150 °C 250 and 500 hours and shear strength was measured subsequently and values were compared to ones non thermal aged. Thickness of intermetallics compounds and its influence to shear strength was investigated.

Test of wettability of lead-free solders

This paper deals with wettability of widely used lead-free solders. Tested solders were lead-free solders Sn-3,8Ag-0,7Cu, Sn-4Ag, Sn-1Cu and Pb containing solder Sn-37Pb. Wetting balance method was used for testing wettability of the solders mentioned above according to standard ČSN EN 60068-2-54. Temperature of melted solder was 235 °C for Sn-37Pb and 248 °C for lead-free solders. Wetting was tested for copper and nickel in form of wire with diameter 1 mm and length 20 mm. Samples were dipped into melted solder and total force actuating in time during the test was measured. Key parameters for characterization wetting behavior of solder were maximum wetting force and the time to reach 2/3 of that force. The influence of nitrogen atmosphere was tested as well.

Determination of BGA solder joint detachment cause - warpage effect

Many aspects such as different materials used during the electronic assembly, increasingly finer dimensions of components, different processes and their settings have an influence on reliability of electronics products. This article deals with BGA assembly, specifically the determination of BGA solder joint detachment cause - with a warpage effect. Samples for diagnostic were obtained from manufacturer, who already pointed to the probable problematic location (BGA component) by electric in-circuit test. Cross-section of BGA assembly was made and an open joint - thin longitudinal gap between BGA component and solder joints connection was observed. The task was to identify a cause that produced axial detachment of BGA solder ball from component pads. The use of Scanning Electron Microscopy (SEM) determined that detachment was caused by a warpage effect.

Mechanical stress tests of SMT attachments

This paper covers experiments conducted on the specimens of different lead-free SMT assembly technologies. This research aimed specifically at the properties of lead-free solders and Electrically Conductive Adhesives (ECA) subjected to mechanical stress, applied as cyclic bending of experimental circuit boards. The experiment performed in past showed different properties of both technologies and their influence on the reliability of electronic devices under mechanical stress. These experiments are closely connected with the influence of thermal-induced mechanical stress on the reliability of electronic circuits.

Study of influences on the changes of the surface tension

The knowledge of actual value of surface tension is important for the understanding to several soldering aspects, such as wetting, joint shape, fluxing action and, particularly, for the quantification of solderability testing. High surface tension is required for wave soldering. Values of surface tension are mainly caused by measurement conditions (temperature, ambient -air, inert atmosphere of the different composition etc.). In measurements we changed conditions such as temperature of the molten solder, oxygen concentration and surface finish of part of the sample, which is immersed under molten solder. Together with the change of these conditions we ware able to measure changes of the wetting force, which is given by the change of the surface tension.

Whiskers growth on thick tin layers and various types of surfaces

The transition from a highly widespread lead solders to lead-free solder alloy types meant many changes in the electrical industry. This transition has brought many technological phenomena that deserve our attention and they have to be still addressed in order to improve the quality and reliability of manufacturing printed circuit boards. One of them is the presence of small crystalline formations on the surfaces of tin and some tin alloys which are called whiskers. This article focuses on the influence of the used electrical materials and their surface treatments on the growth of tin whiskers. For our experiment were selected two lead-free solders with a high percentage representation of tin, by which are Sn95,5Ag3,8Cu0,7 (SAC 387) and Sn99Cu1. Solders were plated in a thick layer on the three types of metal substrates with various surface finishes. For this experiment was chosen copper, brass and phosphor bronze. The created samples were exposed to static mechanical stresses of compressive force under the action of permanent constant temperature at 50 degrees of Celsius.

Post-curing behavior of two-component Electrically Conductive Adhesive

Electrically Conductive Adhesives (ECAs) are already widely used in the electronic industry, often deployed even in adverse conditions. Because of this, a series of accelerated climatic experiments was taken. During these tests, an interesting behavior of the two-component ECAs was observed: a quick, sharp drop of electrical resistance in a short time after the curing of the ECA. This indicated a possible problem with the stability of two-component ECAs and thus it mandated further research. Its results are published in this paper and seem to support the validity of the original finding - and suggest a possible risk when using certain conductive adhesives.

Wetting Force Measurement of the Different Types of Solders and Testing Materials

We have used one of the most commonly used wetability evaluation methods -wetting balance (meniscograph) method to measure the wetting force. We have made a modification of the measuring equipment to measure a less quantity of the solder. We have measured a combination of different types of the lead and lead-free solders and different types of the testing materials. The measurement was carried out on nine different types of solders (Sn63Pb37, Sn95Sb5, Sn95Sb3,5Cul,5, Sn96Ag4, Sn95,5Ag3,8Cu0,7, Sn97Bi2Cul, Sn97Cu3, Sn99Cul, Sn99,75), three types of testing materials (copper, nickel and brass) and three types of fluxes. All measurements nine solders ware measured in ambient atmosphere and two lead-free solders were (Sn96Ag4, Sn95,5Ag3,8CuO,7) measured in inert atmosphere. The results of measurements we classified into the table according to he shape of wetting curve and according to the visual control.