In this aspect, the new material class for 3D-MID performs well. However, the passive test only provides values at room temperature. Whereas normally, a crack induced metallization failure occurs at maximum expansion which is the case at peak test temperature. Therefore, additionally, a total of 18 specimen per substrate material were tested using active resistance measurements during 2000 cycles. The resistivity ranged between 0.1 Ω and 0.5 Ω and was measure using the four-point probe measurement method as described in [6, 7]. An exemplary plot of a resistance measurement history is displayed in Fig. 3 (top). In Fig. 3 (bottom) the results show that except for the samples #35 (~6% change) and #36 (~55%) the absolute maximum resistance change remains below the defined threshold of five percent. The failed sample #35 was analyzed metallurgically but no clear cause for the defect could be identified. #36 showed failed readings in the measurement device. Still, based upon the reliability results the material performs better than its thermoplastic counterparts in . This makes it an appropriate substitution as 3D-MID base material.
By looking at the metallization in metallographic micro-sections the interface between substrate and metallization was examined. The general metallization exhibits an aperiodic rippled roughness on the bottom side (compare Fig. 4, column b) indicating a mostly mechanical adhesion to the substrate . Regarding deteriorations in the layers partially some voids in the copper nickel interface can be observed after 500 cycles on substrate 1 in Fig. 4, mid c). After 1000 cycles a small delamination area on substrate 2 is detected which is not obvious by electrical resistance measurement, indicated by a red square in Fig. 4, bottom. Generally, the nickel layer surface on top on both substrates exhibits beginning small vertical cracks after 500 and 1000 cycles. Other changes in the interface between thermoset substrates and metallization seem to be too small to detect by optical microscopy. Even though cracks seem to start growing from the top nickel side between 500 and 1000 cycles, the metallization track reliability is higher than average solder failure at such test standard. Therefore it may be regarded sufficient for 3D-MID use.
(Top) Layout for packaging encapsulation test with 3D geometries. (Top right) Microsection of encapsulated silicon dummy chip with copper terminals in material 1. Encapsulation thickness is about 400μm on the top side and 500μm on the bottom. Inside the silicon a large crack is visible. (Bottom) A total of four vias were laser drilled and metallized on this sample of substrate 2. All vias have electrical conductive connection to the copper terminals. On the right copper terminal there is a delamination visible between silicon and copper.
Micro sections show that there are slight delamination and voids at the interface of chip and mold. Also for some samples during the molding process cracks were induced into the silicon Fig. 6 (top right). Delamination in the contact area of via and copper terminal could not be detected. Thus, the new mold materials may be used as packaging material with respect to electrical connectivity even after thermo-mechanical stress testing. On the other hand the crack initiation presumably caused during the injection mold process does not allow this process to be used with active chips at the moment. Optimization of the tooling is required to avoid cracks which are most likely due to an uneven pressure distribution in the molding process causing bending of the silicon.
The influence of the ablation depth on the Hot-Pin-Pull adhesion measurement is a slight increase in pull force. However this increase could not be determined with statistical significance. As demonstrated in  the laser structuring settings influence the amount of ablated material. Optimal parameters depend on laser settings, i.e. depth of circuit tracks, and the substrate material. The authors in  concluded that from a packaging point of view the conductor track surface should be above the substrates surface or only slightly deepened to allow for sufficient wetting between component and solder. The laser setting therefore is not as crucial for the adhesion and circuit track reliability as it is for soldering which is a crucial property in electronics packaging.
The overall conductor track reliability is high for both tested materials. Out of a total of 96 test samples only one failed the thermal shock test of 2000 cycles with the strict criterion of five percent resistivity increase. The results are better or comparable to other 3D-MID studies with thermoplastic materials . Based on the results regarding the conductor track reliability the evaluated materials with the LDS free process perform sufficiently to be used in 3D-MID applications.
Abstract:Desiccation cracking of cohesive soils is the development of cracks on the soil surface as a result of a reduction in water content. The formation of desiccation cracks on the cohesive soil surface has an undesirable impact on the mechanical, hydrological, and physicochemical soil properties. Therefore, the main aim of this study is to experimentally and numerically investigate eco-friendly soil improvement additives and their effect on the desiccation cracking behavior of soils. Improvement of soil crack resistance was experimentally studied by conducting desiccation cracking tests on kaolin clay. Biopolymer xanthan gum and recycled carpet fibers were studied as potential sustainable soil improvement additives. In addition, image processing was conducted to describe the effect of an additive on the geometrical characteristics of crack patterns. The results show that the soil improvement additives generally enhanced the soil strength and reduced cracking. Furthermore, a hydro-mechanical model was developed to predict the moisture transfer and onset of desiccation cracks in plain and amended kaolin clays. Data obtained show that the inception of the desiccation cracking and radial displacements were delayed in the improved soil specimens, which is in agreement with the experimental data.Keywords: desiccation cracking; biopolymers; cohesive soils; image processing; hydro-mechanical model; green ground improvement engineering
The concept of crack tip opening angle (CTOA) was probably introduced by Anderson in 1972  to simulate stable crack growth by the finite element method. In this method, crack growth is obtained by successive relaxation of the nodal forces at the node representing the crack tip. The y angle between two element sides representing the crack tip was chosen as the criterion for the crack growth. However, crack growth dependence of this angle was expected, and a constant value was used for all of the stages of growth. The value at the first increment of crack growth called y 0 was determined from the experimentally determined criti cal value of the J integral. Anderson assumed that after large crack growth, steady state conditions prevail and y stabilizes to the y stab value with y stab < y0. Rice  has pointed out the difficulty of using this parameter for the simulation of crack growth in an elastic-plastic material. In this case, displacement exhibits a profile proportional to the product r (where r is the distance measured from the crack tip). Therefore the tangent at the crack tip corresponds to an ambiguous definition of the CTOA.
One of the first experimental determinations of the CTOA was mentioned by Luxmoore et al. . Using centre notched and double-edge notched specimens of aluminium alloy, they measured the CTOA during stable crack growth. They noted that the crack tip opening 8 varied linearly with increases in crack length. This linear behaviour indicated that the CTOA remains constant and equal to 2.1°. This was also previously noticed by de Koning et al. .
Conditions of stable crack growth require that the rate of change of the crack driving force with increasing crack length Aa is smaller than the increase of crack growth resistance expressed in terms of crack opening displacement:
During the last decade, extensive studies applying the CTOA concept to ductile fracture have been undertaken. As a result, the CTOA-based fracture mechanics method has become mature, and a standard test method for critical CTOA testing was developed recently by ASTM with the designation E2472-06e 1 . The recommended specimens are the compact-tension C(T) and middle-crack-tension M(T) specimens made from thin-sheet materials in order to achieve low constraint conditions at the crack tip. The standard was validated by Heerens and Schodel  using a comprehensive dataset on the stable crack extension in an aluminium sheet material with a thickness of 3 mm.
The CTOA fracture criterion has now become one of the most promising fracture criteria used for characterizing stable tearing in thin metallic materials. Initially, fracture resistance to crack extension was given by Charpy energy, as in the Battelle two-curves method (BTCM) . The Charpy test is related to crack initiation, bending of the specimen, and plastic deformation at the load points. It is necessary that tests performed to characterize the propagation resistance be able to isolate and quantify the propagation energy with respect to incremental crack advance. For this reason and due to the development of higher strength steels with increased toughness and lower transition temperatures by using controlled rolling techniques, Charpy energy was replaced by drop-weight tear test (DWTT) energy in the HLP two-curve method . DWTT tests are also related to crack initiation, bending of the specimen, and plastic deformation. However, notched DWTT specimens are larger 2b1af7f3a8