Plastic Encapsulated Microcircuits Research Articles

Evaluation of Copper and Gold Wire Bonds in PEM Devices

Abstract The shift from gold to copper wire bonds used in plastic encapsulated microcircuits (PEMs) has been gradual for the last few years. Many agencies and critics question the long-term robustness and reliability of copper wire bonds; however, PEM manufacturers have been thoroughly evaluating and optimizing the copper wire bond process over the last few years to produce highly reliable products. When the manufacturing process is optimized and closely controlled and monitored, copper wire bonds can be a reliable and stronger alternate to gold wire bonds. This paper details a copper wire bond study that specifically compares copper wire against gold wire bonds following combined environmental life stress test conditions. In this study, bond pull testing indicates good performance of both copper and gold wire bonds. The methods used in this analysis (destructive physical analysis, wire pull testing, and environmental testing) were effective techniques for evaluation of bond wire integrity, detection of manufacturing defects, and overall assessment of copper and gold wire bond processes. Based on wire bond testing in this analysis, the reliability and integrity of optimally developed copper wire bonds appear to be superior to or even stronger than gold wires in the same package type. Equivalent reliability was demonstrated for both copper and gold wire bonds in this test.

Analysis of Scanning Acoustic Microscopy Problems for Plastic Encapsulated Microcircuits with Complex Structure

In order to keep up with the development trend of plastic encapsulated technology and effectively improve the Scanning Acoustic Microscopy (SAM) capability of Plastic Encapsulated Microcircuits (PEMs) with complex structure, the structural characteristics of complex packaging devices, the limitations of ultrasonic technology and the applicability of testing standards are systematically studied. The influence of complex package structure and chip coated structure on SAM detection is analysed. The influence of the limitation of ultrasonic technology on the thickness and number of layers of PEMs is studied. Finally, the applicability of SAM test standards is discussed. Through the research, many problems in the SAM detection of PEMs with complex structures are pointed out, and some test requirements and suggestions on test standards are given.

Effect of Environmental Factors on Ultrasound Detection of Plastic Encapsulated Microcircuits

Based on the problems encountered in ultrasonic detection of Plastic Encapsulated Microcircuits (PEMs), the relationship between storage environment, immersion time, baking treatment and temperature test and other environmental factors and the stability of PEM are studied for the characteristics of plastic encapsulated materials that are susceptible to temperature changes and moisture. And its effect on the results of ultrasonic testing, the reasons for the inconsistency of ultrasonic testing results are analysed, and storage, transportation, immersion time, baking treatment requirements before and after the test, and device use recommendations are put forward.

Popcorning Failures in Polymer and MnO2 Tantalum Capacitors

Popcorning is a well-known effect in plastic encapsulated microcircuits (PEM) and it occurs in chip tantalum capacitors. The sensitivity of components to the presence of moisture during soldering is characterized by the moisture sensitivity level (MSL); however, contrary to PEMs, there is no standard procedure for establishing MSL for tantalum capacitors. The effect of absorbed moisture on soldering related degradation and failures in tantalum capacitors have not been studied properly yet, and there is no sufficient information regarding the difference in the sensitivity to soldering between polymer and MnO2 capacitors. In this work, 16 types of polymer and 9 types of MnO2 tantalum capacitors with different moisture content have been tested before and after reflow soldering. The level of moisture release during soldering has been estimated and thermo-mechanical analysis used to assess deformation of capacitors during soldering simulations. Results show that moisture uptake in similar parts is approximately two times greater in polymer than in MnO2 capacitors. Cracking of the case and degradation of parameters can occur in both types of parts, but MnO2 capacitors are much more likely to fail catastrophically with a short circuit and possible ignition during the first power-on cycle. This type of failure in MnO2 capacitors is lot-related, can occur even at derated voltages and relatively low levels of moisture sorption that corresponds to room conditions. Baking before soldering is an effective measure to prevent failures even in lots susceptible to popcorning damage.

Evaluation of CSAM for Plastic-Encapsulated Microcircuit Dormant Storage Testing

Rigorous environmental testing, with C-mode scanning acoustic microscopy (CSAM) inspection, was imposed on a sizeable set of exemplary commercial off-the-shelf plastic encapsulated microcircuits (PEMs) to demonstrate their suitability for dormant storage over extensive periods of time. After qualification testing of over 4800 samples of 39 standard manufacturer (mfr) part numbers from 18 world-class mfrs in 25 widely different PEM package types, indications of product discrepancies by CSAM were largely discounted based upon device reliability testing, including physical cross sectioning.

Voids in Electronic Parts Yield to Ultrasound

Abstract Acoustic microscopy is an effective method for detecting voids in plastic-encapsulated microcircuit (PEM) packages.

Research on Failure Mechanism of Plastic Encapsulated Microcircuits

Plastic encapsulated microcircuit (PEM) had been invented in the 60s of the 20th century, with great advantages in size, weight, cost and performance. Nevertheless, there are still great differences between PEMs and high reliable devices and many problems cannot be ignored, such as corrosion, popcorn effect and low-temperature stratification. In this paper, common failure modes and their mechanisms of PEMs have been discussed according to some typical failure cases, which can provide an important basis for improving the process technology and enhancing the reliability of PEMs.

Reliability analysis and utilization of PEMs in space application

More and more plastic encapsulated microcircuits (PEMs) are used in space missions to achieve high performance. Since PEMs are designed for use in terrestrial operating conditions, the successful usage of PEMs in space harsh environment is closely related to reliability issues, which should be considered firstly. However, there is no ready-made methodology for PEMs in space applications. This paper discusses the reliability for the usage of PEMs in space. This reliability analysis can be divided into five categories: radiation test, radiation hardness, screening test, reliability calculation and reliability assessment. One case study is also presented to illuminate the details of the process, in which a PEM part is used in a joint space program Double-Star Project between the European Space Agency (ESA) and China. The influence of environmental constrains including radiation, humidity, temperature and mechanics on the PEM part has been considered. Both Double-Star Project satellites are still running well in space now.

Vapor Pressure and Residual Stress Effects on Mixed Mode Toughness of an Adhesive Film

Temperature- and moisture- induced delamination leading to popcorn package cracking is a major package reliability issue for surface-mount plastic encapsulated microcircuits (PEM). Crack propagation along one of the interfaces of a ductile adhesive joining two elastic substrates is modeled to study interface delamination and toughness of PEMs. The polymeric adhesive is stressed by remote loading and residual stress. Along the crack front, the film-substrate interface is modeled by a strip of cells that incorporates vapor pressure effects on void growth and coalescence through a Gurson porous material relation. Results show that under high levels of vapor pressure, increasing film thickness will produce smaller enhancement on the steady-state fracture resistance of the interface, also referred to as the joint toughness. Across all mode mixity levels, vapor pressure effects dominate over residual stress. The adverse effects of vapor pressure are greatest in highly porous adhesives subjected to a strong mode II component. The latter is representative of the likely state of loading in IC packages since residual stress, resulting from the film-substrate thermal mismatch, induces a predominantly mode II component.

Vapor pressure and residual stress effects on failure of an adhesive film

Surface-mount plastic encapsulated microcircuits (PEM) are susceptible to temperature- and moisture-induced failures during reflow soldering. Adhesive failures in PEMs are studied using a model problem of a ductile adhesive joining two elastic substrates. The polymeric adhesive contains a centerline crack. The adhesive film is stressed by remote loading and residual stresses. Voids in the adhesive are pressurized by rapidly expanding water vapor. The computational study addresses three competing failure mechanisms: (i) extended contiguous damage zone emanating from the crack; (ii) multiple damage zones forming at distances of several film thicknesses ahead of the crack; and (iii) extensive damage developing along film–substrate interfaces. The second failure mechanism is found in low porosity adhesives, while the first is dominant in high porosity adhesives. The first is also the likely failure mode when voids in the adhesive are subjected to high vapor pressure. The third damage mechanism is operative in low porosity adhesives subjected to high residual stress. In general, both residual stress and vapor pressure exert pronounced effects on failure modes. Vapor pressure, in particular, accelerates voiding activity and growth of the damage zone offering insights into the catastrophic nature of popcorn cracking.

Wire-bond failure mechanisms in plastic encapsulated microcircuits and ceramic hybrids at high temperatures

Ceramic hybrids are the preferred solution when long-term high-temperature reliability is required, but standard plastic encapsulated microcircuits (PEMs) are an interesting alternative due to low price and high availability. Test vehicles with standard PEMs were subjected to thermal ageing at 150–175 °C. Six of eight vehicles failed after only three weeks at 175 °C, and the cause of failure was found to be microcracking at the interface between gold ball and aluminium bond pad giving rise to resistance increase. The intermetallic region was formed during high-temperature lead soldering and continued to develop during thermal ageing. The high-temperature performance of aluminium wire bonding to a selection of thick film metallizations on ceramic substrate was also investigated. Gold–palladium has previously been reported as a high-temperature solution, but we found that the mechanical strength of aluminium to gold–palladium (AuPd) degraded seriously at temperatures above 200 °C due to intermetallic formation. Aluminium to silver thick film plated with copper and nickel showed good mechanical strength and unaltered electrical resistance after four weeks thermal ageing at 250 °C.

Critique of EIA SSB-1: guidelines for using plastic encapsulated microcircuits and semiconductors in military, aerospace, and other rugged applications

Economics and availability concerns, together with internal directives, have provided a strong impetus for the military and aerospace electronics industries to use commercial plastic encapsulated microcircuits (PEMs) in their applications. To address concerns related to the reliability of commercial devices in these harsh environment applications, the G-12 Solid State Device Committee of the Government Electronics & Information Technology Association (GEIA) has developed guidelines for assessing the suitability of plastic encapsulated microcircuits and semiconductors for use in military, aerospace and other rugged applications. These guidelines were recently published in the Electronic Industries Alliance Engineering Bulletin. The concept of these guidelines is a step in the right direction, as they provide direction to industry on how to incorporate PEMs reliably. They provide an approach to assess the use of PEMs that correctly separates manufacturer quality and part reliability issues. Furthermore, the guidelines recognize that failure can occur by multiple failure mechanisms that are excited by many different environmental factors, not just temperature. However, the guidelines omit several critical elements from their evaluation plan that are present in other approaches, the reliability assessment does not directly account for component architecture in its calculations, and the approach uses constant failure rate statistics and parts count methodologies to evaluate system reliability. This last characteristic has caused some to indicate that the guidelines bear strong similarities to MIL-HDBK-217, which has been precluded from military use. This paper provides a critique of the SSB-1 Guidelines.

An assessment of the value of added screening of electronic components for commercial aerospace applications

Historically many aerospace original equipment manufacturers (OEMs) have required military-like screening, in addition to the component manufacturers' quality assurance processes, when using non-military components. The published literature [Commun. Reliab. Maintainab. Supportab. (1994) 14–19; Plastic-encapsulated microcircuits in high reliability applications, Realiability and Maintainability Symposium, Anaheim, CA, 1994; Commun. Reliab. Maintainab. Supportab. (1994) 60–63; Int. J. Microcircuits Electron. Packaging 20 (1997) 36–40] is not conclusive regarding the value of the added component screening. In this paper, we conclude that the added component screening provides no value for most non-military grade components and may even lower their in-service reliability. However, the added screening does provide value for a limited set of low-quality components. To maximize the benefits to the whole supply chain, OEMs should apply screening only to the low-quality components.

Reliable use of commercial technology in high temperature environments

Over 97% of all integrated circuits produced today are available only in plastic encapsulated, surface mountable, commercial grade or industrial grade versions. This is especially true for the most advanced technologies, such as high-speed microprocessors. The cost, availability, and functionality advantages of these devices are causing many electronics manufacturers to consider using them in elevated temperature applications such as avionics and automotive under-hood electronic systems to ensure early affordable access to leading edge technology. However, manufacturers only guarantee the operation of commercial devices in the 0°C to 70°C temperature range, and industrial devices in the −40°C to 85°C temperature range.This paper describes the first study which addresses the reliability of plastic encapsulated microcircuits (PEMs) in the range from 125°C to 300°C, well outside the manufacturer's suggested temperature limits. Previous work has indicated that PEMs sold for use in the commercial and industrial temperature ranges can often operate within the manufacturer's suggested electrical parameter specifications at much higher temperatures. For example, in this study the Motorola MC68332 microcontroller, which is widely used in avionic systems, remained fully functional to 180°C. This is in accordance with previous work that indicated no fundamental constraints to the operation of silicon devices at temperatures up to 200°C. However, this study also revealed that industrial grade, plastic encapsulated MC68332 devices had less than half the lifespan at 180°C than similar MC68332 devices packaged in hermetic ceramic packages. In addition to the MC68332, the other nine types of plastic components studied had a shorter lifespan at 180°C than their ceramic packaged counterparts. Outgassing of flame-retardants with the associated catalysis of the growth of intermetallics was determined to be the principal cause of failure in the plastic components.Further studies conducted on 84-lead plastic quad flatpack (PQFP) leadframes encapsulated in two different molding compounds revealed that the plastic encapsulant itself begins to lose its ability to insulate leads at temperatures greater than 250°C and can actually combust at temperatures greater than 300°C. Both insulation resistance degradation and cracking were found to be more prevalent in novalac than biphenyl. In summary, these studies have shown that while plastic encapsulated microelectronics can operate at temperatures above 125°C, they have less than half the life of ceramic microcircuits at 180°C and they begin to show signs of insulation resistance degradation after 300 hours at 250°C.

Do we need a PEM reliability model?

Reliability prediction models for microcircuits have been a function of steady state temperature. Failure rates generated from accelerated temperature tests were extrapolated to predict system reliability at system use temperatures. This is now known to be completely inaccurate. Attempts are now being made to predict the reliability of plastic-encapsulated microcircuits (PEMs) based on accelerated temperature/humidity testing. Failure rates generated owing to corrosion failure mechanisms at these high stress levels are then extrapolated and used to predict system reliability at use temperature/humidity conditions. This paper discusses the fallacy of this approach. A new concept for assurance of PEM corrosion resistance is proposed. It will be shown that today's best commercial practice suppliers have already addressed the design, materials and processing issues of moulded packaged microcircuits, and corrosion is no longer a mechanism of concern to the user. Copyright © 1999 John Wiley & Sons, Ltd.

Development of test vehicles for evaluating plastic-encapsulant reliability and improving thermal conductivity of encapsulant materials

Abstract Plastic-encapsulated microcircuits (PEMs) are proposed for use in military systems to reduce cost and eliminate long-lead items such as packages and lids. Encapsulant materials must be evaluated for compatibility with devices and fine-wire bonds, and electrical stability on deposited elements and integrated-circuit devices. Reliability evaluations in screen tests and various temperature/humidity/bias environments are also essential prior to use in advanced packaging. Encapsulant reliability evaluation requires a test vehicle (MCM-C and MCM-L) to identify these key performance characteristics to assure environmental and mechanical protection because no complete multichip test vehicle, however, is available for use. An encapsulant test vehicle in previous work was modified by substituting a Sandia ATC04 chip and a silver-comb-pattern array with varying feature sizes, using only a single nichrome-resistor network, and adding a deposited comb pattern. The unpassivated resistor and a silver-comb pattern offer both a go/no-go and quantitative test for screening encapsulants and the Sandia chip facilitates stress measurements on the die as well as thermal dissipation evaluation with resistance heaters on the chip. An industry-standard encapsulant, Hysol® FP 4450, was modified to improve thermal conductivity. Exact filler selection and loading were optimized, balancing dispensability, wear, and flow characteristics. Control materials (Hysol® FP 4450) and improved, thermally conductive versions were exposed to short-term screen tests, long-term humidity, and elevated temperature storage testing. Thermal conductivity of Hysol® FP 4450 was improved by approximately 200% and both materials were comparable in temperature/humidity/bias and highly accelerated stress testing as well as thermal cycling and elevated temperature storage.

Low temperature delamination of plastic encapsulated microcircuits

Plastic encapsulated microcircuits (PEMs) are increasingly being used in applications requiring operation at temperatures lower than the manufacturer’s recommended minimum temperature, which is 0°C for commercial grade components and −40°C for industrial and automotive grade components. To characterize the susceptibility of PEMs to delamination at these extreme low temperatures, packages with different geometries, encapsulated in both biphenyl and novolac molding compounds, were subjected to up to 500 thermal cycles with minimum temperatures in the range −40 to −65°C in both the moisture saturated and baked conditions. Scanning acoustic microscopy revealed there was a negligible increase in delamination at the die-to-encapsulant interface after thermal cycling for the 84 lead PQFPs encapsulated in novolac and for both 84 lead PQFPs and 14 lead PDIPs encapsulated in biphenyl molding compound. Only the 14 lead novolac PDIPs exhibited increased delamination. Moisture exposure had a significant effect on the creation of additional delamination.

A Review of Changes and Trends Affecting Military Electronics Manufacturing

Dramatic business changes in the aerospace and military defense industries have caused contractors to drastically alter their design and manufacturing processes. These changes appear to have been influenced by recent events or movements: the U.S. Department of Defense initiative (Perry, 1994; U.S. Department of Defense, 1994) discourage dependence on military specifications/standards (the “Perry Initiative”) which resulted in trends within the electronics industry to use commercial materials in typical military environments (alternative component initiatives). Consequently, changes are underway regarding some of the traditional technologies used in defense electronics. Specifically, this paper will present an overview of the changing nature of some of these technologies, e.g., interconnections, coatings, and plastic encapsulated microcircuits (PEMs), and the standards/practices related to these from a manufacturing aspect. The information provided is by no means all-inclusive, but it does identify a focus for increased discussion and study.

A critique of the Reliability Analysis Center failure-rate-model for plastic encapsulated microcircuits

As the use of plastic encapsulated microcircuits (PEM) has escalated in the electronics industry, especially in applications in which "mission" success must be accomplished at "any cost", some researchers have proposed reliability models to predict their failure rates or mean times-to-failure. One organization that took on such a challenge was the US Dept. of Defense (DoD) Reliability Analysis Center (RAC). Despite its admirable aims, the model has inherent limitations which result in unrealistic predictions, which could negatively affect parts selection, environmental management and logistics support. This paper presents an analysis of the model developed by the RAC.

Plastic encapsulated microcircuit reliability predicition: why?

Reliability prediction models for microcircuits have been a function of steady-state temperature. Failure rates generated from accelerated temperature tests were extrapolated to predict system reliability at system use temperatures. This is now known to be completely inaccurate. Attempts are now being made to predict the reliability of plastic encapsulated microcircuits (PEMs) based on accelerated temperature/humidity testing. Failure rates generated due to corrosion failure mechanisms at these high stress levels are then extrapolated and used to predict system reliability at used temperature/humidity conditions. This paper discusses the fallacy of this approach. A new concept for the assurance of PEM corrosion resistance is proposed. It will be shown that today's best commercial practice suppliers have already addressed the design, materials, and processing issues of molded packaged microcircuits, and corrosion is no longer a mechanism of concern to the user.