Martin Placek

Flux effect on void quantity and size in soldered joints

Abstract This article is focused on both macro and microvoids in soldered joints and the use of additional flux to reduce their frequency and minimize their negative effect on the soldered joint reliability. In total five fluxes were used, three were gel based (NC559, MTV-125R, TSF-6516) and two of them were liquid based (Topnik G-5, JBC FL-15). They were used within two solder pastes, both lead and lead-free. The reflow process was identical for all of the combinations and was within the range of manufacturer recommended profiles. The amount of voids was evaluated using X-ray analysis. It was found that the use of increased amount of proper flux, specifically flux with higher activity, in the solder paste may significantly lower the void occurrence.

Study of influence of thermal capacity and flux activity on the solderability

During the surface mount technological process the assembled PCB is exposed to heat when molten solder alloy wets the surfaces and creates future solder joints. The PCB with all components should ideally be exposed to the same temperature profile during the soldering process. The temperatures differ throughout the PCB due to different thermal capacities of used materials and components even though the temperature profile is stable. The aim of the study was to assess the solderability of the copper material with different thermal capacity and to consider the effect of different types of fluxes. The measurement was done by wetting balance method, where the wetting force is measured as a function of time during which the test specimen is immersed into, remains immersed and then it is pulled out from the solder bath. In our experiments we used copper wire of four different diameters (0.7 mm, 1 mm, 1.5 mm), three types of solders - one lead (Sn63Pb37) and two lead free (Sn99Cu1, Sn97Cu3) solders and three types of fluxes.

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.

Monitoring of metalized film capacitors degradation with impedance nonlinearity measurement

Self-healing capacitors fabricated of metalized polypropylene film as the dielectric material are widely used in power electronics. Self-healing process makes elimination of local defects in these capacitors possible and extends the life-time of them. It was shown that the measuring of capacitor V/A characteristic nonlinearity is usable and effective tool for monitoring of capacitor quality. Six capacitors of this type were aged in an oven at the temperature of 90 °C for 1000 hours under normal ambient conditions and changes caused by ageing were monitored with the nonlinearity measurement. It was found that nonlinearity of capacitor grows with the time of ageing.

Solder joint quality evaluation based on heating factor

Purpose The purpose of this paper is to increase the reliability of manufactured electronics and to reveal reliability significant factors. The experiments were focused especially on the influence of the reflow oven parameters presented by a heating factor. Design/methodology/approach The shear strength of the surface mount device (SMD) resistors and their joint resistance were analyzed. The resistors were assembled with two Sn/Ag/Cu-based and one Bi-based solder pastes, and the analysis was done for several values of the heating factor and before and after isothermal aging. The measurement of thickness of intermetallic compounds was conducted on the micro-sections of the solder joints. Findings The shear strength of solder joints based on the Sn/Ag/Cu-based solder alloy started to decline after the heating factor reached the value of 500 s · K, whereas the shear strength of the solder alloy based on the Bi alloy (in the measured range) always increased with an increase in the heating factor. Also, the Bi-based solder joints showed shear strength increase after isothermal aging in contrast to Sn/Ag/Cu-based solder joints, which showed shear strength decrease. Originality/value The interpretation of the results of such a comprehensive measurement leads to a better understanding of the mutual relation between reliability and other technological parameters such as solder alloy type, surface finish and parameters of the soldering process.

Wetting balance test — Comparison of solder alloys wetting

The article deals with wetting balance method comparison of solderability of the following materials combinations: two lead free solder alloys (Sn99Cu1, Sn95.5Ag3.8Cu0.7), one leaded solder alloy (Sn63Pb37), one soldering substrate type — copper wire (0.7 mm diameter) and four type of fluxes. The surface of tested samples was additionally evaluated by subjective optical analysis. The results confirm that the best results were achieved for Sn63Pb37 solder alloy — it has the fastest wetting speed (lowest zero cross time). Out of the lead free solder alloys, better results were achieved with Sn95.5Ag3.8Cu0.7 solder.

Comparison of mechanical resistance of SnCu and SnBi of solder joints

Mechanical stress act on solder joints during transport, function and storage of the electronic equipment. Therefore, the knowledge of solder joints resistance against it is very useful. This article deals with comparison of mechanical resistance of SnCu0,7 and Sn42Bi58 solder alloys. The experiments were based on two PCBs (smaller and larger one, with soldering pads designed according to commonly used chip package) which were soldered together. Surface finishes of soldering pads were OSP, ENIG and HASL. Mechanical test were based on sharp tip, which were driving between two PCBs. From overall point of view a slightly better results were achieved for Sn42Bi58 solder alloy. Additionally the thicknesses of intermetallic layers were compared and voids frequency inside solder joints were inspected.

Ultrasonic soldering, mechanical properties of solder joints

Mechanical properties of solder joints have influence on reliability of electronic products. Therefore the knowledge of the mechanical behavior of solder joints is very important. This article deals with comparison of mechanical properties of solder joints prepared with conventional soldering methods and ultrasonic soldering methods. Material for samples preparation was based on two PCB (material FR4) with soldering pads which were soldered together. As solder alloy was used Sn965Ag3Cu0.5 for convention soldering method and active soldering alloy for ultrasound soldering. The mechanical resistance, changes according to used surface finishes the highest share strength, have been achieved for solder joints which ware prepared by ultrasonic soldering on pads with copper surface finish, worst results were achieved for pads with ENIG and HASL surface finishes.

Substrate influence on temperature distribution along the PCB during vapor phase soldering

This article is focused on measurement of temperature gradients in different locations on test-boards during Vapor Phase Soldering (VPS) with different materials as PCB substrates. VPS is usually applied in electronics assembly technologies due to its ability to heat the board fast and uniformly during reflow soldering. The heating rate differs significantly even on a moderate size PCB. The measurements were performed on different substrates, particularly on FR4, FR4 with aluminum core, ceramic, and polyimide flexible board samples. The temperature gradients were uniform with low heat capacity boards, contrary, the high heat capacity aluminum based PCB showed significant non-uniformity in heating, where observed temperature differences reached up to 20 °C.

Influence of latent heat on the shape of temperature profile for different types of solder alloys

Temperature profile is a very important parameter which has a high impact on reliability issues in electronic assembly manufacturing. The wrong shape of temperature profile (temperature/cooling gradients, maximum temperature, preheat together with flux activation) can lead to issues like flux/solder spattering, pad cratering, unwetting, excessive interrmetallic growth, tombstone effect shrinkage etc. This article deals with influence of latent heat on the shape of temperature profile, which starts to be more attractive due to higher integrity of electronics equipment. The experiments were based of two lead-free solder alloys (Sn96.5Ag3.5, Sn96.5Ag3Cu0.5), which were remelted on the copper pads in continual convection furnace. The temperature profile, were measured directly under the copper pads. Results shows, that the measured temperature profiles under soldering pads differs against the temperature profile which were measured on the PCB. Additionally the temperature profiles which were measured under soldering pads differ according to used solder alloys as well.