The effect of lead free soldering on formation of black pad failure
By this time usable solder alloys for lead-free soldering had already been developed. NEMI (National Electronics Manufacturing Initiative) recommends Sn/3.9Ag/0.6Cu (±0.2%) solder alloy for reflow soldering instead of leaded solder alloys, due to its excellent mechanical properties and other good parameters. The next step is the choosing of suitable pad finish for lead-free soldering. In the age of fine pitch assemblies (QFPs (Quad Flat Pack), BGAs (Ball Grid Array) and CSP (Chip Size Package)) flat and planar plated surfaces are needed. Electroless Nickel Immersion Gold (ENIG) pad finishes are used, when there is a need for aluminum wire bonding besides soldering. At the interface of NiAu plating and the solder a failure can occur, called 'black pad'. Black pad is not only a cosmetic problem, but also a source of weak wire bonding and soldering joints. The question is, whether the lead free soldering affects the formation of black pad failure or not. Experiments were made to answer this question, and this paper will show the results.
Vibration response of printed circuit board in wide range of temperature. Characterization of PCB materials
Stiffness of printed circuit boards (PCB) has a great impact on reliability of solder joints. Vibrations or external stress loading lead to stress accumulation within solder joint area. Depending on intensity, inducted stress can be relieved by creep or fractures of solder joint. Intensity of inducted stress depends on loading conditions as well as properties of joined materials (specially stiffness of printed circuit boards).Crucial parameters such as stiffness and Tg depends on the producer of laminate. Therefore accurate evaluation of PCB material is a basis for improvement of equipment reliability. Nowadays, when the number of producers and the mass of FR4 laminate imported from Asia is rapidly increasing, it is specially important to have the complete knowledge about parameters of used materials. Dedicated, designed stand will be applied to determine vibration response of printed circuit boards. The novel solutions implemented will ensure high accuracy of measurements. Proposed method for vibration response characterization will be cheaper to standard method that bases on scanning laser vibrometer. The stand will be used to determine changes of FR4 stiffness in wide range of temperature (for example from − 20 to 130 °C) and Tg parameter. Within the frame of the paper, measuring stand and the results of performed evaluations are described
"Flying Triangulation" - a new optical 3D sensor enabling the acquisition of surfaces by freehand motion
In order to obtain complete 3D surface information of an object it is often necessary to acquire many partial 3D views. For this purpose, the sensor has to be moved (e.g. for the acquisition of sculptures or rooms). Further, in many cases a motion of the object relative to the sensor is unintended but inevitable (e.g. for medical applications such as intraoral measurements of teeth). Nearly all existing optical 3D sensors either lack an easy handling or require a standstill during the acquisition of a single partial 3D view, since usually multiple camera shots have to be taken for this purpose. This makes such measurements elaborate or even impossible.