bonding, handling, and mounting procedures for millimeterwave phemt mmic?s m/a-com products rev. v4 application note M570 1 ? north america tel: 800.366.2266 ? europe tel: +353.21.244.6400 ? india tel: +91.80.43537383 ? china tel: +86.21.2407.1588 visit www.macomtech.com for addi tional 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.
bonding, handling, and mounting procedures for millimeterwave phemt mmic?s m/a-com products rev. v4 application note M570 2 ? north america tel: 800.366.2266 ? europe tel: +353.21.244.6400 ? india tel: +91.80.43537383 ? china tel: +86.21.2407.1588 visit www.macomtech.com for addi tional 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. die down method resultant thermal resistance temperature required high temperature capabilities power handling capability ease of operation special equipment required potential problems conductive epoxy good with proper technique room temp to 150 ? c good low to medium power easiest to apply little to none high series or thermal resistance soft solder i.e., pb-sn-ag (90,5,5) pb-sn (60,40) good to very good 200 - 280 ? c 180 - 200 ? c good good to very good for low or high power simple application heated stage hot gas bonder or gas curtain and furnace flux is usually required with lead solders. cleaning of flux must be done carefully eutectic solder au-sn (80,20) sn-sb (97,3) very good approx. 300 ? c approx. 230 ? c good very good simple application heated stage or hot gas bonder needs clean reducing atmosphere die bonding with conductive epoxies - lnas although satisfactory die down bonds may be obtained using these epoxies, the po wer amplifiers may not per- form to specification. the low noise amplifiers work well when epoxies are used. the following precautions should be observed to obtain consistently strong bonds. the low noise die are back metallized with pd/ni/au (100/ 1,000 / 30,000?) metalliz ation. thermally and electrically conductive epoxy is recommended for die- mounting the low noise die, although au/sn eutectic preforms can be used. table 1. selection guide for die down bonding techniques figure 1. die bonding criteria the attachment surface should be clean and flat. electri- cally conductive epoxy is required and must be within the warranty shelf and/or pot life. it is advisable to use half the listed pot life. silver conductive epoxies should not be used where they will come into contact with lead tin solders or high tin solder. there can be an anodic reac- tion which may cause failure of the bond. epotek h2oe or ablestick 84-1lmi is recommended. a minimum amount of epoxy should be applied, then the die should be placed into position. figure 1 shows good and unacceptable bonds.
bonding, handling, and mounting procedures for millimeterwave phemt mmic?s m/a-com products rev. v4 application note M570 3 ? north america tel: 800.366.2266 ? europe tel: +353.21.244.6400 ? india tel: +91.80.43537383 ? china tel: +86.21.2407.1588 visit www.macomtech.com for addi tional 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. curing of the epoxy should follow the manufacturer?s recommended schedule. they epoxy must be cured in air or oxidizing atmosphere since the reaction requires oxygen. the epoxy oven should be clean and have good air flow. the epoxy will not cure well if there are other solvent fumes in the atmosphere. the carrier fluid must not be a llowed to flow on the top of the chip. not only will it make the chip un-bondable, it will be almost impossible to detect under normal bonding procedure. if a vacuum tip is used to put the chip in place, remove the vacuum wh en the chip is 10 mils from the epoxy. static charge will hol d the chip to the tip. if the vacuum tip touches the epoxy, it will become coated with the epoxy carrier flui d and contaminate the next chip. this same problem may occur with the use of tweezers. the tweezers should be cleaned before pick- ing up another chip if they touch the epoxy. the shear bond strength of a good epoxy joint can ap- proach that of solder 50-100 kgms/cm2. the thickness of the conductive epoxy should be kept at 0.001? or less. the shear bond strength should be about: 40-60 grams for 0.010 x 0.010 inch chip 150-250 grams for 0.020 x 0.020 inch chip 350-500 grams for 0.030 x 0.030 inch chip in general, the epoxy will shear before the chip breaks. weak bonds are usually caused by the use of old epoxy, bonds that are too thick, or lack of cleanliness. visual inspection die down bonds should be checked with a 5-15x micro- scope and should meet the visual criteria shown in table 2. top contacting methods the usual criteria for choosing a specific top bonding technique are the size of the top contact of the chip, the type of chip, the sensitivity of the chip to temperature and pressure, the type of circuit board, and the equip- ment available. usually, the simplest contacts are a gold 0.0007 to 0.001 inch diameter wedge bonded gold wire. the inductance of a 1 mil diameter wire will be ~0.5 nh for a 0.20 inch long lead. this inductance can be re- duced considerably by using multiple contact wires. it is very difficult to give definite parameter values of force pressure time and temperature for an optimum bonding schedule. different wire, bonding surfaces, or die characteristics require different bonding conditions. gaas is very brittle and extra care should be taken when wire bonding. in general, the bonding parameters should be adjusted to maximize reproducibility at a high bond pull strength. die down method visual (good bond criteria) typical bond strength (in stress) extra rs1 from die down (0.020? chip) conductive epoxy flat, maximum epoxy thickness approx. 0.001 inch 90% min. wetting approx. 50-100 kgms/cm2 less than 0.1 ohms soft solder flat, maximum epoxy thickness approx. 0.001 inch 90% min. wetting approx. 70-100 kgms/cm2 less than 0.1 ohms gold-tin eutectic solder flat, maximum epoxy thickness approx. 0.001 inch 90% min. wetting approx. 100-150 kgms/cm2 less than 0.1 ohms 1. 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)
bonding, handling, and mounting procedures for millimeterwave phemt mmic?s m/a-com products rev. v4 application note M570 4 ? north america tel: 800.366.2266 ? europe tel: +353.21.244.6400 ? india tel: +91.80.43537383 ? china tel: +86.21.2407.1588 visit www.macomtech.com for addi tional 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. wedge bond with 1.0 mil diameter gold wire or 3.0 mil x 0.0005 mil ribbon and a force of 18 to 22 grams. bonds should be started on the die and terminated on the pack- age, if possible. for rf connections, two wires are rec- ommended. most bonding pads are 4.0 x 4.0 mils and most input and output pads are 4.0 x 4.0 mils. most problems are caused by improper bonding machine and tool settings as well as improper maintenance and cleanliness. it is important to control the movement of the part being bonded, alignment of tools, tool height, angle, and tool condition. in general, the die will crack or ?crater? if too hard a wire or excessive pressure is used. too little pressure results in small, weak bonds. a good wire bond should be stronger than the wire and should also be two or three times the wire diameter. when wire bonding, the de- formed width of the wire shoul d be about 1.3 to 1.8 times the wire thickness. if the deformed width is too small, the bond will tend to lift off. if it is too large (greater than 1.8 times the wire diameter) the wire tends to weaken and break. figure 2 shows the relationship between the pull strength and the deformed width of the ultrasonic bonded wire. acceptable bonds wire does not separate when tested no fractures in bond no separation of metallization wire breaks before bond unacceptable bonds wire separates from bond bond fractures at weld separation of metallization from dice table 3. bond strength criteria (gold wire or strap) bond strength pull test it is extremely important to maintain good quality control procedures in order to ensure good bonding. figure 3 and table 3 illustrate criteria for visual inspection and for testing on bond strength. capacitors and resistors it is recommended that capacitors and resistors are selected that meet at l east the same temperature ranges as the mmics. the following are recom- mended devices to use. capacitors dielectric laboratories 100 pf p/n d30bh101k5pk or equivalent 1000 pf p/n d35bv102kpx or equivalent resistors mini-systems, inc. 10 wp/n mstf-2st-10r00j-g or equivalent wire or ribbon size (inches) minimum pull strength (grams) 0.0007 wire diameter 1.5 0.001 wire diameter 3.0 0.002 wire diameter 9.0 figure 2. pull strength vs. deformation for a wirebond figure 3.
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