Analytical elasto-creep model of interfacial thermal stresses and strains in trilayer assemblies

A two-dimensional model has been developed for thermal stresses, elastic strains, creep strains, and creep energy density at the interfaces of short and long trilayer assemblies under both plane stress and plane strain conditions. Both linear (viscous) and non-linear creep constitutive behavior under static and cyclic thermal loading can be modeled for all layers. Interfacial stresses and strains are approximated using a combination of exact elasticity solutions and elementary strength of materials theories. Partial differential equations are linearized through a simple finite difference discretization procedure. The approach is mathematically straightforward and can be extended to include plastic behavior and problems involving external loads and a variety of geometries. The model can provide input data for thermal fatigue life prediction in solder or adhesive joints. For a typical solder joint, it is demonstrated that the predicted cyclic stress–strain hysteresis shows shakedown and a rapid stabilization of the creep energy dissipation per cycle in agreement with the predictions of finite element analysis.     

进口松香型焊膏的成分分析

本文采用离心分离的方法沉淀出松香型焊膏的无机组分，并用发射光谱测定无机成分；优选了氯仿：95％乙醇：25氨水：水＝35：30：2：2（体积比）作为焊膏有机组分的薄层色谱展开剂，在薄层板上呈现清晰的4个斑点，以此展开剂作为柱色谱的流动相，成功地分离了各种有机组分，并采用红外、质谱等手段鉴定了所含组分的结构。     

电解分离-ICP-AES测定铜-银-磷钎料中的磷

采用电解法分离铜后,电感耦合等离子体-原子发射光谱法直接测定了铜-银-磷钎料中磷的含量。实验表明,在1.0moI·L^-1硝酸电解液中可以使铜基本电离完全,对磷的测定不产生干扰。在最佳的测定条件下,该法用于铜-银-磷钎料中磷的测定,回收率在98.3%—102.4%之间,相对标准偏差2.28%。     

An experimental investigation of the temperature field in small piezoelectric vibrators

The temperature field in small piezoelectric vibrators is investigated experimentally. First of all, the effects of the solder points and internal loss of small piezoelectric vibrators on the non-uniformity of the temperature field are investigated. It is found that the solder points increase the temperature of adjacent piezoelectric material, and the non-uniformity of the temperature field increases as the internal loss increases. Then, the placement method of the piezoelectric vibrators on the temperature field is investigated. It is found that the placement method has a remarkable effect on the maximum temperature rise of the piezoelectric vibrators. Finally, the transient temperature field and its effect on the operation of the vibrators are investigated. It is found that the input power of the vibrators may fluctuate greatly during the transient process of the temperature field.     

Flux growth of a new cobalt-zinc-tin ternary phase Co7+xZn3−xSn8 and its relationship to CoSn

The intermetallic compound Co_7+xZn_3−xSn₈ (−0.2<x<0.2) forms from the reaction of cobalt in zinc/tin eutectic flux. This phase has a new structure type in orthorhombic space group Cmcm, with unit cell parameters a=4.138(1) Å, b=12.593(4) Å, and c=11.639(4) Å (Z=2; R₁=0.0301). Varying the amount of cobalt in the synthesis leads to formation of a superstructure in space group Pnma, with lattice parameters a=12.5908(2) Å, b=11.6298(3) Å, and c=8.2704(2) Å (Z=4; R₁=0.0347). A Co/Zn mixed site and a partially occupied Co site in the Cmcm structure order to form the Pnma supercell. TGA/DSC studies indicate that the binary phase CoSn initially forms in the flux at 1173 K, and then reacts with the zinc in the cooling solution to form the ternary structure at 823 K. This phase exhibits Pauli paramagnetic behavior.     

Qualitative electroless Ni/Au plating considerations for the solder mask on top of sequential build-up layers

Advanced printed circuit boards (PCBs) with sequential build-up (SBU) layers require alternating dielectric and copper layers on top of a core substrate. This can be achieved by lamination of resin coated copper (RCC) or by coating of dielectric polymers followed by copper deposition. The plating of electroless Ni/Au used as a solderability preservative on top of sequential build-up layers is investigated. For this application a solder mask polymer has to be applied in order to separate solder pads. Experiments showed that on parts of the underlying build-up layer exposed to the electroless Ni plating solution electroless Ni can grow. This overplating is caused by the remains of colloidal Pd/Sn catalyst on top of the build-up layer from preceding electroless Cu deposition. At very small features skipping of the plating can also take place. The overplating and skipping phenomena are influenced by a number of parameters, such as the temperature, the concentration of the stabilizer and pH. The dimensions of features on the board and the thickness of the solder-mask polymer also influence skipping. Based on qualitative analyses of the skipping and overplating phenomena rules of thumb for the solder mask design based on the plating conditions are proposed.     

Solder joint inspection based on neural network combined with genetic algorithm

To improve the performance of automatic optical inspection (AOI), a neural network combined with genetic algorithm for the diagnosis of solder joint defects on printed circuit boards (PCBs) assembled in surface mounting technology (SMT) is presented. Six types of solder joint have been classified in respect to the reality in the manufacture. The images of solder joint under test are acquired and 14 features are extracted as input features for the classification. The neural network is easily become over-fitting because these input features are not independent of each other, so the genetic algorithm is introduced to select and remove redundant input features. The experimental results have proved that the neural network combined with genetic algorithm reduced the number of input feature and had a satisfying recognition rate.     

Automatic Full Strain Field Moiré Interferometry Measurement with Nano-scale Resolution

Moiré Interferometry (MI) theoretically can provide real-time full strain field measurements in dynamic environment. So it’s extensively used in reliability analysis of electronic packaging. Due to the nature of specimen preparations procedure, the optical noise is usually too strong so that an accurate phase-based information processing is not possible. In this paper, a 164 nm/pixel spatial resolution Moiré Interferometer with automated full strain field calculation is proposed. Provided by two-level zooming system, the high spatial resolution increase the signal intensity and eliminate some optical noise which allows accurate full strain field map generated automatically by the combination of phase shifting technique and continuous wavelet transform (CWT). Furthermore, the calculation procedure of CWT proposed here does not require unwrapping and differentiation, which avoid the possible numerical noise introduced in these two steps. In the proposed system, pixel by pixel in-plane strain tensors will be calculate from the intensity map of interferograms using phase-based method. The resulting strain tensor can be used to model constitutive relationship or compare with finite element analysis results. A thermal experiment on BGA packaging is used to demonstrate the advantages of the proposed new design.     

Depth dependence of angular dips: Measurements and calculations for H+ and D+ in Si and Ge

The variation of shape of angular dips with penetration depth has been investigated by the backscattering technique for 0.3 to 1.5 MeV protons and deuterons impinging on Si and Ge single crystals at different temperatures.

Since the depth dependence of the angular dips at small depths is unknown the comparison between the experimental critical angle ψ _1/2 determined at non zero penetration and the theoretical values obtained at zero depth is ambiguous.

Yield profiles vs. penetration depth have thus been calculated accounting for the nuclear and electronic reduced multiple scattering.

The obtained results justify quantitatively both the magnitude of the experimental data and their dependence on the target temperature, ion energy and penetration depth.

The disagreement previously reported between the figures calculated at zero depth and the extrapolated experimental values results from the strong variation ψ_1/2 of near the crystal surface.