Optimization and validation of thermal management for a RF front-end SiP based on rigid-flex substrate

This paper mainly presents a new 3D stacking RF System-in-Package (SiP) structure based on rigid-flex substrate for a micro base station, with 33 active chips integrated in a small package of 5cm × 5.5cm × 0.8cm. Total power consumption adds up to 20.1 Watt. To address thermal management and testability difficulties of this RF SiP, a thermal test package is designed with the same package structure and assembly flow, only replacing active chips with thermal test dies (TTDs). Optimization and validation of thermal management for the thermal test package is conducted. Effects of the structure, chip power distribution, and ambient temperature aspects on the thermal performance are studied. Thermal vias designed in the organic substrate provide a direct heat dissipation path from TTDs to the top heatsink, which minimizes junction temperature gap of the top substrate from 31.2 °C to 5.3 °C, and enables junction temperatures of all the chips on the face to face structure to be well below 82 °C. Chip power distribution optimization indicates placing high power RF parts on the top rigid substrate is a reasonable choice. The ambient temperature optimizes with forced air convection and cold-plate cooling method, both of which are effective methods to improve thermal performances especially for this micro base station application where environment temperature may reach more than 75 °C. The thermal management validation is performed with a thermal test vehicle. Junction temperatures are compared between finite-volume-method (FVM) simulation and thermal measurement under the natural convection condition. The accordance of simulation and measurement validates this thermal test method. Junction temperatures of typical RF chips are all below 80 °C, which shows the effectiveness of thermal management of this RF SiP.     

毫米波硅基SiP模块设计

设计了一款采用硅基板作为载体的毫米波上变频微系统系统级封装(System in Package, SiP)模块。该模块利用类同轴硅通孔(Through-Silicon-Via, TSV)结构解决了毫米波频段信号在转接板层间低损耗垂直传输的问题。该结构整体采用四层硅基板封装,并在封装完成后对硅基射频SiP模块进行了测试。测试结果显示,在工作频段29～31 GHz之间,其增益大于27 dB,端口驻波小于1.4,且带外杂散抑制大于55 dB。该毫米波硅基SiP模块具有结构简单、集成度高、射频性能良好等优点,其体积不到传统二维集成结构的5%,实现了毫米波频段模块的微系统化,可广泛运用于射频微系统。     

LTCC在SiP中的应用与发展

SiP是实现先进电子设备小型化、多功能化和高可靠性的有效途径。SiP的组装和封装载体是基板。LTCC通过采用更小的通孔直径、更细的线宽/线间距和更多的布线层数能实现SiP复杂系统大容量的布线。通过采用空腔结构可以优化系统元器件的组装,提高散热能力。利用埋置无源元件,可以减少SiP表贴元件的数量。利用3D-MCM和一体化封装可以进一步减少系统的面积和体积,缩短互连线。未来SiP的发展要求LTCC具有更好的散热能力、更高的基板制作精度和更多无源元件的集成。     

Thermo-mechanical finite element analysis in a multichip build up substrate based package design

This paper presents a thermo-mechanical analysis of a multichip module (MCM) package design, with emphasis on the package warpage, thermally induced stress and the second level solder joint reliability. The MCM package contains four flip chips which are mounted on a build up substrate. First, the effect of the positioning of four silicon dice within the MCM package on the warpage of the package is studied. Second, the effect of package dimensions (the heat spreader thickness, the structural adhesive thickness and the substrate thickness) on the maximum residual stress as well as the warpage of the package is performed. Finally, this paper presents a 3D sliced model for solder joint reliability of the MCM assembly. A creep constitutive relation is adopted for the 63Sn/37Pb solder to account for its time and temperature dependence in thermal cycling. The fatigue life of solder joint is estimated by the Darveaux's approach. A series of parametric study is performed by changing the package dimensions. The results show that the largest die tends to experience highest stresses at its corner and has more influence on the warpage of the package than smaller dice. The results also show the most sensitivity factors that affect the package warpage and the second level solder joint reliability are the substrate thickness and the heat spreader thickness. The structural adhesive thickness has no major effect on the package warpage, the maximum von Mises stress of the package and the second level solder joint reliability.     

Fast reliability qualification of SiP products

For the purpose of rapidly identifying the functional weak points of SiP products and defining appropriate design rules, a new methodology is proposed to achieve fast reliability qualification. This new methodology is based on the moisture absorption behavior along the critical interface of a SiP carrier and on the most sensitive zone to delamination of the SiP carrier, determined by simulation and experimentally checked. In this paper, a new accelerated preconditioning is proposed and a new non destructive thermal method to monitor the delamination is presented. The effectiveness of this new stress test to accelerate the failure mechanism of the SiP carrier and the ability to detect delamination are evaluated by performing a DOE.     

LTCC基板缺陷分析及改善对策

针对低温共烧陶瓷(LTCC)基板生产过程中遇到的对位偏差缺陷问题,从材料、工艺、设备、环境条件等多个方面做了详细的分析和验证。排除了打孔误差、印刷误差、叠片误差等非关键性影响因素,确定了导致偏差的根本原因是生瓷片变形所致的开腔误差以及打孔机的累积误差。提出了通过控制环境温湿度、缩短加工周期来减小生瓷片变形量以及对错位区域进行补偿的措施,解决了产品的缺陷问题,提高了产品的合格率,产品一次合格率达到95%。     

基于LTCC技术的Ku波段四通道T/R组件研制

基于相控阵雷达的应用需求,利用LTCC多层基板技术,研制了Ku波段四通道T/R组件。该组件通过三维布局实现了组件的小型化和轻量化,同时也保证了射频、电源和控制的信号完整性。通过微带线变换带状线的优化设计,实现了良好的传输性能,提高了四通道信号间的隔离度。腔体内部做了隔墙设计,避免四通道的信号干扰,保证一致性。最终研制实现的小型化Ku波段四通道T/R组件,尺寸仅为70 mm×37.8 mm×11.5 mm,质量约53 g,组件接收增益大于25 dB,噪声系数小于4 dB,发射功率大于16 W。该T/R组件四通道一致性好,性能稳定,具有较好的应用价值。     

Photovoltaic module reliability model based on field degradation studies

Crystalline silicon photovoltaic (PV) modules are often stated as being the most reliable element in PV systems. This presumable high reliability is reflected by their long power warranty periods. In agreement with these long warranty times, PV modules have a very low total number of returns, the exceptions usually being the result of catastrophic failures. Up to now, failures resulting from degradation are not typically taken into consideration because of the difficulties in measuring the power of an individual module in a system. However, lasting recent years PV systems are changing from small isolated systems to large grid‐connected power stations. In this new scenario, customers will become more sensitive to power losses and the need for a reliability model based on degradation may become of utmost importance. In this paper, a PV module reliability model based on degradation studies is presented. The main analytical functions of reliability engineering are evaluated using this model and applied to a practical case, based on state‐of‐the‐art parameters of crystalline silicon PV technology. Relevant and defensible power warranties and other reliability data are obtained with this model based on measured degradation rates and time‐dependent power variability. In the derivation of the model some assumptions are made about the future behaviour of the products—i.e. linear degradation rates—although the approach can be used for other assumed functional profiles as well. The method documented in this paper explicitly shows manufacturers how to make reasonable and sensible warranty projections. Copyright © 2008 John Wiley & Sons, Ltd.     

Integration of ultra-wideband slot antenna on LTCC substrate

An ultra-wideband slot antenna realised in low-temperature cofired ceramic (LTCC) technology is reported. The antenna is developed for a single-package solution of ultra-wideband radio. The radiating element of the antenna has a shape of ellipse 11 mm wide and 17 mm long. It shares the ground plane with other radio circuitry and is fed through a microstrip line 41 mm long and 3 mm wide. The experimental result shows that the prototype antenna achieved a bandwidth of 7.6 GHz (return loss S11/spl les/-10 dB or VSWR 2:1 from 3 to 10.6 GHz). The antenna radiation patterns at 3.5, 6.85 and 10.1 GHz are also presented.     

LTCC应用于大功率射频电路的可能性研究

通过介绍低温共烧陶瓷（LTCC）技术工艺及其优势，研究其在微电子工业特别是大功率RF电路中应用的可行性。     

基于列车监测网络设备的射频功放模块设计

列车关键设备及行车状态的无线实时监测是列车安全运行的有效技术保障,而如何延长无线监测节点通信距离、增强通信可靠性成为研究重点。本文提出适用于列车监测特殊环境的射频功放模块设计方法,采用集成化芯片RF5110G避免内部干扰,通过滤波电路和阻抗匹配优化电路板设计,所设计的功放模块很好地解决了列车特殊环境导致的信号衰减问题,增强了监测网络节点数据传输可靠性,为列车监测、维护提供了可行的方法。     

基于AVR单片机的高可靠性开关量模块的设计

从提高开关量输入输出模块可靠性的角度出发,针对微处理器软件看门狗的漏洞及死机恢复后控制状态保持的特点,给出两套解决方案。模块以功能集成度较高ATmega64L单片机为主控芯片,采用三电源供电,对数据采集和数据通信硬件均采用光电隔离技术,给出软硬件设计的详细过程;模块数据通信采用MODBUS_RTU通信协议,并给出了力控软件调试界面。模块设计体现了抗干扰能力提高的同时,更靠近实用化、工业化、产品化。     

Extraction of substrate parameters for RF MOSFETs based on four-port measurement

In this work, a new method for extracting substrate parameters of radio frequency (RF) metal oxide semiconductor field effect transistors (MOSFETs) based on four-port measurement is presented. A T-liked substrate resistance network is used and the values of all components in the cold MOSFETs were extracted directly from the four-port data between 250 MHz and 8.5 GHz. The output admittance Y/sub 22/ can be well modeled up to 26.5 GHz based on the extracted substrate resistances and the other extrinsic capacitances extracted from an active device.     

X波段三维异构片式收发SiP模块设计

采用硅基三维异构集成技术,在极小的体积内,将多个微波单片集成电路(MMIC)和无源功分网络一体化集成,实现了一种X波段4通道片式收发系统级封装(SiP)。该SiP由2个体硅堆叠封装(PoP)而成,不同封装通过球栅阵列(BGA)方式互连,单层封装的内部腔体上下面均贴装芯片,封装内部采用硅通孔技术(TSV)实现垂直互连,SiP尺寸为14 mm×14 mm×3.2 mm。测试结果表明,在8~12 GHz内,SIP 4个通道的发射饱和输出功率≥30.5 dBm,接收增益≥24.5 dB,噪声系数≤3 dB,接收输入P_-1≥-26 dBm,同时具备6位数控移相和6位数控衰减功能,重量约1 g,可广泛用于微波收发系统。     

Comparative analysis of accelerated ageing effects on power RF LDMOS reliability

We present in this paper results of comparative reliability study of three accelerated ageing tests applied on power RF LDMOS: Thermal Shock Tests (TST, air-air test), Thermal Cycling Tests (TCT, air-air test) and High Temperature Storage Life (HTSL). The two first tests are carried out with a drain current flowing through the device during stress. The results obtained show the variation and the Device’s performance quantitative shifts for some macroscopic electric parameters such as threshold voltage (V_th), transconductance (G_m), drain-source current (I_ds), on-state resistance (R_{ds_on}) and feedback capacitance (C_rs) under various ageing tests. To understand the degradation phenomena that appear after ageing, we used a new electro-thermal model implemented in Agilent’s ADS as a reliability tool.     

Thermo-mechanical reliability of a multi-walled carbon nanotube-incorporated solderable isotropic conductive adhesive

Carbon nanotubes (CNTs) are considered as ideal candidates for the reinforcement of polymer composites due to their superior physical properties. In this paper, in order to investigate the influence of multi-walled carbon nanotubes (MWCNTs) on the reliability properties of solderable isotropic conductive adhesives (SICAs) with a low-melting-point alloy (LMPA), two types of SICAs (with 0.03 wt.% MWCNTs and without MWCNT) were formulated. Thermal shock (− 55 to 125 °C, 1000 cycles) and high-temperature and high-humidity (85 °C, 85% RH, 1000 h) tests were conducted on these samples. The SICA assemblies with and without MWCNTs showed stable electrical reliability properties during reliability testing; this stability was due to the formation of excellent metallurgical interconnection between corresponding metallization by the molten LMPA fillers. Although the mechanical pull strength of SICA assemblies decreased after thermal aging, due to the excessive layer growth and planarization of the IMCs, the SICA with MWCNTs showed enhanced mechanical reliability properties compared with the SICA samples without MWCNTs. This improvement in performance was caused by the enhancement effect of the MWCNTs. These results demonstrate that MWCNTs within SICAs can enhance the reliability properties of SICA joints due to their outstanding physical properties.     

Real‐time reliability test for a CPV module based on a power degradation model

Models based on degradation are powerful and useful tools to evaluate the reliability of those devices in which failure happens because of degradation in the performance parameters. This paper presents a procedure for assessing the reliability of concentrator photovoltaic (CPV) modules operating outdoors in real‐time conditions. With this model, the main reliability functions are predicted. This model has been applied to a real case with a module composed of GaAs single‐junction solar cells and total internal reflection (TIR) optics. Copyright © 2010 John Wiley & Sons, Ltd.