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Bonding, Handling, and Mounting Procedures for Millimeterwave PHEMT MMIC’s M/A-COM Products Rev. V4 Application Note M570 Visit www.macomtech.com for additional data sheets and product information. M/A-COM Technology Solutions Inc. and its affiliates reserve the right to make changes to the product(s) or information contained herein without notice. ADVANCED: Data Sheets contain information regarding a product M/A-COM Technology Solutions is considering for development. Performance is based on target specifications, simulated results, and/or prototype measurements. Commitment to develop is not guaranteed. PRELIMINARY: Data Sheets contain information regarding a product M/A-COM Technology Solutions has under development. Performance is based on engineering tests. Specifications are typical. Mechanical outline has been fixed. Engineering samples and/or test data may be available. Commitment to produce in volume is not guaranteed. Discussion Millimeterwave MMIC's are becoming more common in commercial applications. Their small size and potentially lower cost has made them valuable in the growing mar- ket of millimeterwave systems. Their size and delicate nature also makes them fragile. The following informa- tion is provided to help die users handle, mount, and bond MMIC chips. It should be noted that MMIC's usually require special- ized equipment for die attachment and bonding. These operations require a clean environment and special han- dling equipment such as vacuum pickups, hot gas bond- ers and/or thermal compression and/or thermo-sonic bonding equipment. M/A-COM Tech offers a family of GaAs MMIC amplifiers above 15 GHz. This note addresses: GaAs MMIC Devices Low Noise Amplifiers Power Amplifiers Gain Blocks Driver Amplifiers Handling and Assembling of Chips and Circuits The challenges of handling and assembling chips into packages can be best separated into two areas: putting the chip into the circuit (die down) and making top con- tact to the chip (top bonding). Permanent damage to the MMI C may occur if the pre- cautions are not followed. The MMIC's should be han- dled in a clean room type of environment. All devices are static sensitive, so handling equipment and person- nel should comply with DOD-STD-1686 Class I. Avoid instrument and power supply transients while bias is connected to the MMIC. Use shielded signal and bias cables to minimize inductive pick-up. In general, DO NOT touch the surface of the die. It is recommended that the MMIC die be handled with vacuum pick-up tools with rubber or soft material or handled along the long side with tweezers. Chip Bonding Methods A recommendation for improved bonding is to plasma clean the carrier before any eutectic is used. The MMIC should be plasma cleaned before wire bonding. A risk in using MMIC's is the possible damage incurred when assembling chips into circuits. In general, the value of the MMIC circuits e xceeds the cost of the MMIC chip itself. When packaged MMI C's are used, the critical die attach and top contact operations are performed by M/A-COM Tech and all devices are RF tested after assem- bly into the packages. When the circuit fabricator performs the die attach and wire bonding operation on a complex substrate, he/she runs the risk of losing or damaging a chip during the bonding operation whic h can result in the loss of the whole circuit or in an expensive rework cycle. The most common issues that arise when bonding MMIC's to the circuit are: the introduction of excessive series resis- tance, especially under forward bias conditions due to the improper bonding of the chip to the ground plane; poor reli- ability due to the entrapment of contaminates under the bond; and mechanical failur e of the bond under thermal shock or temperature cycling. All three conditions are the result of improper wetting of the die to the ground plane and are usually caused by inadequate cleanliness or inadequate bonding conditions. Table 1 provides helpful information in the selection of die down techniques. Chip Die Down Bonding Techniques Eutectic Bonding of Chips - Power Amps The eutectic bonder is one of the most convenient ways of bonding chips onto a metal ground plane or circuit. Both silicon and GaAs chips may be bonded using similar tech- niques. GaAs power die are back metallized with Ti/Au metalliza- tion. The use of gold tin solder perform (80% Au, 20% Sn) with an eutectic melting point of 295 ± 5 ˚C is recommended. A clean, flat, gold plated surface is required to insure good wetting. The preform should be large enough to insure that the die fits within the areas sh own, should be ~1 mil thick, and should be 10% smaller than the die itself. During the attaching process, the die collet should be “scrubbed,” rubbed into the eutectic, to ensure a good die attach. The carrier of package temperat ure and collet temperature should be 295 ± 5 ˚C. There should be a 90/10 nitrogen/ hydrogen gas applied to the bonding surface. When the forming gas is applied ensure that the bonding surface tem- perature does not fall below the recommended temperature. This should be done only for the die. All other components - 50W lines, caps, resistors - should be done with electrically conductive epoxy. DO NOT expose the die to a tempera- ture greater than 320˚C for more than 20 seconds.
Visit www.macomtech.com for additional data sheets and product information. changes to the product(s) or information contained herein without notice. and/or prototype measurements. Commitment to develop is not guaranteed. typical. Mechanical outline has been fixed. Engineering samples and/or test data may be available. Commitment to produce in volume is not guaranteed. should be observed to obtain consistently strong bonds. Table 1. Selection Guide for Die Down Bonding Techniques Figure 1. Die Bonding Criteria or Ablestick 84-1LMI is recommended.
Visit www.macomtech.com for additional data sheets and product information. changes to the product(s) or information contained herein without notice. and/or prototype measurements. Commitment to develop is not guaranteed. typical. Mechanical outline has been fixed. Engineering samples and/or test data may be available. Commitment to produce in volume is not guaranteed. other solvent fumes in the atmosphere. ing up another chip if they touch the epoxy. of the conductive epoxy should be kept at 0.001” or less. In general, the epoxy will shear before the chip breaks. bonds that are too thick, or lack of cleanliness. 0.0007 to 0.001 inch diameter wedge bonded gold wire. duced considerably by using multiple contact wires. die characteristics require different bonding conditions.
- This is the approximate extra RF series resistanc e from an ideal lossless bond of a 0.020” x 0.020” chip.
Table 2. Visual Inspection for Good Die-Down Bonds (Using a 5-15x Microscope)
Visit www.macomtech.com for additional data sheets and product information. changes to the product(s) or information contained herein without notice. and/or prototype measurements. Commitment to develop is not guaranteed. typical. Mechanical outline has been fixed. Engineering samples and/or test data may be available. Commitment to produce in volume is not guaranteed. most input and output pads are 4.0 x 4.0 mils. Table 3. Bond Strength Criteria (Gold Wire or Strap)
10 WP/n MSTF-2ST-10R00J-G or equivalent
Figure 2. Pull Strength vs. Deformation for a