Precision guided weapons have made a significant impact during recent armed conflicts in the war on terrorism. These weapons offer increased accuracy resulting in a greater percentage of enemy targets destroyed with less chance of collateral damage. It is estimated that 70% of the bombs used in the recent war in Iraq (Operation Iraqi Freedom) were guided. Precision guided weapons utilize internal advanced electronics packages such as an inertial measurement unit (IMU) in conjunction with a global positioning system (GPS) to home in on a target. These guided munitions are presently the weapon of choice, and ongoing DOD funding efforts indicate a trend toward the production of smaller guided weapons with enhanced accuracy. The increased use of smaller, more accurate precision guided weapons will rely on electronics manufacturing improvements that enable high-g survivability at a reasonable cost. The EMPF, in conjunction with its industry partners, is actively pursuing manufacturing improvements to produce low-cost IMUs (Figure 1-1) for precision guided munitions applications as part of an ongoing Navy ManTech project.

Some of the most widely used guided weapons include the Joint Direct Attack Munition (JDAM), the Paveway laser guided bomb, the Joint Stand-off Weapon (JSOW) and the Tomahawk missile. Of these, the JDAM weapons have been some of the most widely used. The JDAM is a free-falling bomb (1,000 or 2,000 pounds typically) that has a strap-on guidance kit. The kit includes both GPS and inertial capabilities (functions without external reference or communication) and provides guidance to the otherwise "dumb" bomb. JDAMs can be equipped on the Navy F/A-18 fighter aircraft as well as several Air Force fighters and bomber aircraft. Recent JDAMs have had a publicly reported circular error probable (CEP) accuracy of approximately 10 meters. CEP indicates the radius of a circle that encompasses 50% of the impacts from fired weapons. Recent JDAM accuracy improvement offers the potential for CEPs of around 3 meters.

Efforts are underway to produce a new class of precision guided munitions (PGMs). Examples include the Army's Excalibur and the Navy's Extended Range Guided Munition (ERGM) (Figure 1-2). Extending the precision guidance capability to munitions fired from Navy ships would allow precision strikes on enemy targets that are within range of the shoreline. The ERGM round will be fired from a gun barrel on a Navy ship, have the ability to travel a distance of around 50 miles, and impact within meters of its target. The ERGM round is approximately 5 feet long and includes a rocket motor that fires briefly after leaving the gun barrel. The round will be guided by GPS, but will also have a form of inertial guidance known as an Inertial Measuring Unit (IMU). IMUs are units containing both accelerometers to measure linear acceleration, as well as gyroscopes which measure angular rates. The IMU is used initially after launch for guidance prior to the activation of the GPS and can also be critical during the final stages of the mission. For example, during the final approach to the target the GPS signal can be lost or jammed by the enemy. In this scenario, the IMU can complete the mission by leading the round to the target. Guidance information is processed and used to adjust aerodynamic fins on the side of the round in order to change its flight course.

One enabling path to producing precision guided weapons such as ERGMs is to produce functional, gun-hardened IMUs at a reasonable cost. IMUs based on micro electro-mechanical system (MEMS) technology are being considered due to their small size, low-cost and expected long-term reliability. MEMS technology typically refers to small mechanical elements micro-machined into a silicon substrate which also contains circuitry. The U.S. Navy, Army and Air Force are currently committing funds to develop low-cost MEMS IMUs for precision guided munitions.

One of the main technical challenges associated with precision guided munitions is the need for the electronic hardware to operate after withstanding the high g forces (g’s) associated with gun firing. Munitions of this type typically experience gun shocks of 10,000 to 20,000 g’s. Future applications for the Advanced Gun System [AGS] and the 105mm & 120mm rounds for the Future Combat System [FCS] will encounter environments producing a pull in excess of 20,000 g’s.

In addition to high-g survivability, reduced size packaging will enable the production of next generation guidance electronics such as the Deeply Integrated Guidance/ Navigation Unit (DIGNU), which combines the IMU and the GPS receiver into a four to five cubic inch unit. The achievement of smaller, gun-hardened electronic systems may enable new classes of guided weapons such as helicopter fired missiles. Beyond control electronics lies the DOD need for micro-electronic packaging that can be utilized in new fuze programs [MOFA, MFF, HTSF to name a few], seekers and sensors for missiles. The need for high-g survivability, along with the ever increasing demand for higher performance and smaller electronic systems in PGMs, presents the need to establish and demonstrate electronics packaging guidelines for gun-hardened applications.

As part of the effort to manufacture gun-hardened IMUs and related PGM electronics, the EMPF has proposed to develop a set of gun-hardened packaging guidelines based on high-g test data. This guide could be used by numerous DOD manufacturers that make subsystems such as IMUs, GPS receivers, Selective Availability Anti-Spoofing Modules (SAASMs), fuzes and control electronics. The EMPF would select, assemble and test unproven packaging and interconnection approaches in high-g applications. These approaches would provide a definable benefit in terms of high-g survivability, size reduction and cost. The EMPF can leverage its current involvement in the MEMS IMU area as well as its internal packaging capability, knowledge and industry partners. The work performed would establish failure mechanisms for packaging currently being tested in high-g electronics such as wire bonding and flip-chips. Further investigation could include the consideration of more advanced packaging approaches that would enable size reduction techniques such as 3-D chip stacking, stud-bumping of MEMS or the use of folded flex-rigid circuit boards.

The selected packages would be assembled into test articles on the EMPF's demonstration factory floor. The test articles would then be tested at an off-site, established high-g testing facility. The EMPF would use its in-house testing and analysis equipment to perform functional checks and any associated failure analysis. In addition to the high-g survivability data, the EMPF could include the corresponding manufacturing guidelines for package assembly.

Establishing guidelines for gun-hardened electronics would allow all manufacturers of high-g systems and subsystems to draw from a single source for packaging information. The intent would not be to completely mimic the gun-environment, but instead provide high-g test data to enable improved electronic design, component and material decisions for military applications. As next generation products are developed, the high-g test data for packaging would provide a foundation of confidence that certain packaging approaches have merit and should be investigated further. This would not only contribute to the fielding of current and next generation PGMs, but would do so with an emphasis on inexpensive manufacturable packaging solutions.

The level of investment from multiple DOD branches demonstrates the current interest in precision guided munitions. Through the efforts of the Navy ManTech program, the manufacturing technology needed to expand and enhance the attributes of electronics packaging for precision guided munitions can lead to their increased availability and affordability, thus meeting the battlefield needs of today and tomorrow.