Application Notes. Introduction

Transcription

1 Introduction EMC Technology has provided an extensive collection of Application Notes that help designers mount and measure the products. These cover the complete line of Thermopads, Attenuators, SmartLoad, Terminations, and Miniature Delay Lines. Table of Contents Design Kits...58 Thermopad Amplifier Temperature Compensation...59 Thermopad Attenuation Shift Due to Self Heating...60 Chip Device Mounting Instructions...61 Wrapped Chip Device Mounting Instructions...66 SmartLoad Evaluation Board...71 Delay Line...73 Index

2 Thermopad Amplifier Temperature Compensation Application Note 001 Thermopad Amplifier Temperature Compensation The Thermopad is an absorptive microwave attenuator which provides power dissipation that varies with temperature. It is extremely useful as a temperature compensating element. For example, a very common problem with GaAs amplifiers is that the gain of the amplifier varies by db/ C for every db of gain. So a 30 db amplifier would have a gain coefficient of db/ C. The gain of the amplifier can be stabilized over temperature by cascading it with a 6 db Thermopad with a db/ C temperature coefficient (see Figure 1). Also shown in the figure is the amplifier response using the conventional compensation of a PIN diode variable attenuator with DC coupling for bias application, a driver circuit with linear compensation, and a temperature probe. The latter method is more costly, in terms of material, board space, and assembly time; it is less reliable and can produce RF distortion. Figure 1 59

3 Thermopad Attenuation Shift Due to Self Heating Application Note 002 Thermopad Attenuation Shift Due to Self Heating Attenuation shift due to self-heating is not a consideration for low power applications. However, when you design circuits using the Thermopad, it is important to provide proper heat dissipation. The attenuation of the Thermopad will vary with the temperature of the component s resistive film. As the power input to the Thermopad is increased, the film temperature increases. In order to achieve the desired performance, you must know the Thermopad film temperature. The film temperature can be calculated by: Tf = Pd Cth + Ths ( C) where: Pd = power dissipated (W) Ths = heat sink temperature ( C) Cth = thermal conductivity of the Thermopad (W/ C) The Thermopad may be operated at rated power when mounted on a heat sink maintained at 25 C. The input power should be derated linearly to zero at 150 C. If a good thermal connection is made between the heat sink and the Thermopad using thermally conductive epoxy or thermal grease, you may use the following thermal conductances to calculate the film temperature: TVA: 0.2 W/ C CTVA: 0.2 W/ C MTVA: 0.05 W/ C HTVA: 0.05 W/ C For example, the temperature rise across an MTVA0300N05 from nominal temperature (25 C) at the maximum rated power of 0.2W will be: Tf = 0.2W + 25 C = 29 C 0.05W The resulting attenuation shift caused by self-heating will be db. Even when operated at full rated power, attenuation shift of the Thermopad due to self-heating is minimal. 60

4 l ~ [] ~ TSO3XX PLANER & TT3XXX PLANER REF417 ~ ~ SCREENED db VALUE (BLACK) d B GREEN DOT ADD.5dB. TSO3XXW1/WB1 GREEN DOT ADDS.5 db SCREENED db VALUE rl ~ (WHITE) U ~ TSO3XXW3 ~ ~ r~~~ SCREENED db VALUE (BLACK) bzj O ~~--- GREEN DOT ADD.5dB TSO3XXG GREEN DOT ADDS.5 db D SCREENED db VALUE rl (WHITE) U TS93XXT3 SCREENED db VALUE GREEN DOT (BLACK) 5dB SCREENED db VALUE (BLUE) GREEN DOT ADDS.5dB TSO3XXT3 SCREENED db VALUE GREEN DOT (BLACK) db SHEET 1 OF 4

5 I! ~ TSO5XX PLANER VIOLET BACKGROUND ADDS.5 db REF417 ~ ~ SCREENED DOT CODED db VALUE [SEE TABLE] ORIENTATION LINE TSO5XXW 1 /WB 1 REFERENCE TABLE VIOLET BACKGROUND db DOT COLOR db DOT COLOR ADDS.5dB VAL 18t 2nd VAL 18t 2nd 0 BLI< BRN BRN 1 BRN BRN RED 2 RED BRN ORG ~ ~ 3 ORG BRN VEL SCREENED DOT 4 VEL BRN GRN CODED db VALUE 5 GRN BRN BLU 6 BLU BRN VIO [SEE TABLE] 7 VlO BRN GRV 8 GRV BRN WHT 9 WHT RED BLI< 10 BRN BLI< TSO5XXW3 SCREENED DOT CODED dbvalue [SEE TABLE] VIOLET BACKGROUND ADDS.5 db D ~. TSO5XXG VIOLET BACKGROUND SCREENED DOT CODED db VALUE [SEE TABLE] ADDS.5dB ~ D TS95XXT3 VIOLET BACKGROUND ADDS.5 db SCREENED DOT CODED db VALUE [SEE TABLE] TVA PLANER ~ ~ ~ SCREENED db VALUE 3N7 DIRECTION AND SHIFT (BLACK) SHEET 2 OF 4

6 l I.TVA W1/WB1 (NO UNIT MARKING, MARKING ON PACKAGING ONLY) REF417 ~ ~ ~ TVA W3 ~ ~ ~ SCREENED db VALUE 3N7 DIRECTION AND SHIFT (BLACK) TVA G ~ ~ [3-- SCREENED db VALUE 3N7 DIRECTION AND SHIFT (BLACK) TVA9 T3 SCREEN MARKED (BLACK) SCREENED db VALUE DIRECTION AND SHIFT (BLUE) TVA T3 SCREEN MARKED (BLACK) MTVA PLANER ~ n I=l- LASER MARKED db VALUE, ~ U ~ DIRECTION AND SHIFT SHEET 3 OF 4

7 : MTVA W1/WB1 (NO UNIT MARKING, MARKING ON PACKAGING ONLY) REF417 ~ ~ ~ MTVA W3! i ~ ~ ~ N7 LASER MARKED db VALUE, ' 1 DIRECTION AND SHIFT " '1 '1 MTVA G (NO UNIT MARKING, MARKING ON PACKAGING ONLY) ECN '!.., ~ ~ D ~ '1 ".I ii TSO4XX SCREEN MARKED (BLACK) db HTVA (NO UNIT MARKING, MARKING ON PACKAGING ONLY) ~DD SHEET 4 OF 4

8 Chip Device Mounting Instructions Application Note 003 Chip Device Mounting Instructions All of the chip products in this catalog use thick film metallization for terminations either platinum gold, gold, or platinum silver. Each material is used to accommodate the different bonding practices that are commonly used in RF and microwave applications. Some of these chips are offered with wraparound grounds and/or metal tabs. The wrapped parts use the same metallizations noted above for the ground plane. The tabbed parts are available in a variety of base metals and surface finishes. This application note describes the proper mounting technique for ensuring good RF performance, proper heat sinking, and mechanical support. Overview Each of the chip types discussed here is designed for a specific mounting application. Table 1 shows the attachment techniques that are recommended for each of the products. The table is organized by termination type. Consult the product description for each specific part to determine which types are available. Table 1 Recommended Attachment Pretinned Rosin Termination Wire or Solder Solder Solder Core Wire Flip Chip Type Epoxy Die Bond Preform Paste Reflow Solder (Figure 1) Planar Pretinned (S) Gold (G) Three Tabs* (T3) Two Tabs* (T2) One Tab* (T) Wraparound Ground (M) Term X X X X Ground X X X X Term X X X Ground X X X Term X Ground X Term X X Ground X X Term X X Ground X X Term X X Ground X X X X Term X Ground X X X X * See Figure 2 When choosing an attachment technique, the primary concern is to achieve the desired RF performance. All the chip designs have been optimized to perform best when mounted according to the guidelines in Table 1. The most common use for these devices is on a 50 Ohm microstrip transmission line. RF performance will vary with the ground plane spacing under the device, as well as with the dielectric constant of any insulating material. Any device parasitic reactance can usually be compensated for with external circuitry. In general, for attenuation values of 1 through 8 db, capacitance to ground should be minimized. This can be accomplished by using a thick, low dielectric ground plane spacing. For values of 8 db and higher, the best performance is achieved if low inductance ground connections are made. In all cases, grounding is critical. If the device is surface mounted, you must provide plated thru-holes in close proximity to the topside ground pad (Figure 3). For terminating resistors, the same rules apply to the ground connections. For in-line resistors, the parasitic reactances associated with the termination connections must be minimized. This can be accomplished by matching both the chip pad size and the attachment method to the line width of the circuit board. In some cases, a matching circuit is required to optimize the chip performance. continued on next page 61

9 Chip Device Mounting Instructions (continued) Part Preparation Prior to mounting, both the parts and the mounting surfaces must be free of any impurities that may interfere with the attachment process. Common contaminants include finger oils, surface oxides and organic compounds associated with component processing and packaging. Epoxy You may use epoxy bonding for most applications, but be aware that its most serious drawback is outgassing. When used in a sealed package, outgassing can contaminate other parts. We recommend silver conductive epoxies for RF applications. Select the epoxy based on its compatibility with the termination material. Silver epoxy is the best choice for platinum gold and platinum silver terminations. Solvent-free epoxies such as Ablestik 84-1LMI or EPO-Tek H20E are acceptable. The epoxy can be screened or dispensed onto the substrate surface prior to placing the part onto the board. Where possible, an epoxy fillet should be visible to ensure full coverage. To ensure that the part does not move while making the connections, hold the chip in place using non-conductive epoxy. Epoxy preforms may be used for the ground planes of the M and T configurations. Ablestik ECF564A is a suitable conductive film adhesive. When using epoxy preforms, clamp the part in place with a spring clip or a weight to ensure that the preform adheres to both surfaces. Soldering and Circuit Board Considerations As with any other surface mount component, success when soldering depends upon the soldering surface. The size and location of the solder pads is critical. Provide a circuit board pad that is 0.010" to 0.020" over the termination size. Center the pad along the axis of the chip and bias it slightly from each end to allow for a solder fillet. Isolate the pads from the connecting lines to prevent solder wicking. Use either insulating solder dams over the conductors or narrow traces off of the pads. Failure to follow these guidelines can lead to component skewing and/or tombstoning (draw bridge). EMC designed the mounting pads of chips to minimize the possibility of tombstoning 1. Pad size can help minimize tombstoning in two ways. First, by making the pad areas equal, the force from the surface tension of the liquid solder on the two pads will be equal. Second, since the chip is tipped by the lifting moment produced by the solder fillet, the smaller the chip height to pad width ratio is, the smaller will be the resulting lifting force ➁. For flip-chip-mounting of attenuators, see the EMC series of TS0300 and TS0500 components. These are specially designed for surface mount applications. Figure 4 and Figure 5 may be used as guidelines for circuit board designs for TS0300 and TS0500 attenuators, respectively. For reliability reasons, W3 components are best mounted with the attenuator film facing the circuit board. When mounted in this manner, the three terminations that make direct contact to the film also make contact to the traces on the circuit board. Six of the nine terminations of the W3 may be damaged without producing an electrical failure if the part is mounted with the film side down. Flux Flux is a solution used to clean the metal surfaces and remove any oxides prior to soldering. Consult with your solder supplier to determine the best process for your assembly application. EMC chip devices are designed to perform in all solder assembly processes. continued on next page 62

10 Chip Device Mounting Instructions (continued) Solder Preforms Preforms are solid sheets of solder, available with or without flux, that are used primarily for soldering large ground plane areas. Set the preform on a prefluxed surface with the chip positioned over it. Hold the chip in the proper position during reflow with a non-solder wetting jig (e.g., Vespel, stainless steel, aluminum, etc.). Apply pressure to the top of the chip to prevent any trapped air from causing the part to tip, or allowing gaps to form. The scrubbing action of a die bonder can prevent both. Die bonding is commonly performed using a heated stage with the reflow heat produced by a hot air torch or an infrared (IR) lamp. You may also solder the chip using a hot plate or furnace reflow technique. Set the soldering schedule to minimize the duration and intensity of the part exposure to high temperatures. Limit the time on the hot plate to 3 minutes if you are using a good thermally conductive and moderate thermal mass fixture. The short time interval will prevent flux burning and reduce the amount of brittle intermetallic compound formation. To ensure the formation of the proper solder fillet, select a preform size that is 0.005" to 0.010" larger than the size of the solder pad. We recommend Sn 62 Pb 36 Ag 2 solder (178 C eutectic) for all soldering operations. However, soldering temperatures of 250 C for 30 seconds will not damage the parts. Solder Paste Solder paste is a solution of solder, flux, and solvents. Other materials are often added to optimize the screening or dispensing operation. Drying the paste slightly prior to soldering will eliminate any solvents that might boil and cause solder splashes. However, care must be taken not to dry out the flux completely. When large areas must be pasted, screening is the preferred method because it provides an even and repeatable deposition. Deposit the paste onto the substrate either by dispensing or screening. Next, place the chips on the pasted areas. The tackiness of the paste will hold the surface mounted components in place. Next, flow the parts by heating the substrate up to the soldering temperature. Starting with a preheating stage will help reduce the thermal shock to both the parts and the substrate. Follow the preheating with a second-stage heating up to the soldering temperature using an IR, soldering iron, flame, hot air torch, or with a furnace. Profiles of furnaces for various types of solder paste may be found in reference ➂. Pretinning Pretinning is the solder coating of the component and/or the substrate prior to soldering the two together. This is most often accomplished by dipping the parts in a pot of molten solder. Pretin the substrate by plating during fabrication or by depositing and reflowing solder paste. Remove excess solder with a squeegee wipe. Solder the parts using the paste reflow techniques described above. Be particularly careful when pretinning these extremely small parts. Tabs We supply the T, T2, and T3 configurations with tabs already attached to the part. The base metal of the tab is always copper or a copper alloy. The finish is usually gold, however tin, 60/40 tin lead, and 10/90 tin lead finishes are available. Use high temperature (Sn 96.5 Ag C eutectic) solder to attach the tabs to the parts. To reduce the possibility of the formation of any brittle intermetallic compounds at the joints, EMC uses a unique method to remove the gold on the tabs in the area of the solder joint. Use a standard Sn 62 solder to attach these tabs to the circuit board. You may use either paste or wire solder that is melted by reflowing or adding heat with an iron, torch or other localized source. Welding is also acceptable, as long as the solder joint on the part is kept below its melting point (220 C). Cleaning After soldering, clean the substrate to remove any flux or residual solvents. Consult with your solder supplier for the best cleaning method for your application. continued on next page 63

11 Chip Device Mounting Instructions (continued) Wire Bonding EMC supplies chip attenuators (part number suffix G ) with gold terminations for wire and ribbon bonding. Thermal compression and ultrasonic wedge and ball bonding are the most common methods. First, attach the chip to the substrate using epoxy. Heat the substrate to about 150 C. A gold metallic bond will form between the wire and the bonding pad by adding thermal and/or ultrasonic energy while compressing them together. As with the soldering operation, clean all surfaces prior to bonding, as described in the Part Preparation section. Figure 1 Figure 2 Figure 3 continued on next page 64

12 Chip Device Mounting Instructions (continued) Figure 4 Figure 5 References ➀ Erickson, David. How to Design for Manufacturability. Surface Mount Technology. February ➁ Giordano, Jerry and David Khoe. Chip Resistor Design Helps Prevent Tombstoning. Surface Mount Technology. August ➂ Manko, Howard H. Solders and Soldering. McGraw Hill, Inc.,

13 Wrapped Chip Device Mounting Instructions Application Note 004 Wrapped Chip Device Mounting Instructions This line of microwave attenuators is designed for surface mount and wraparound grounding applications. The W1 has a platinum gold wraparound ground with full back metallization and platinum gold input/output terminations. The WB1 has a platinum gold wraparound ground and gold input/output terminations for wire bonding. The W3 type has wraparound metallization on all three terminals with small contact pads on the back side. This application note describes the mounting techniques for each attenuator type to optimize RF performance, heat sinking, and mechanical support. Overview Each of the three wraparound configurations is designed for a specific mounting application. As with many surface mount devices, the electrical connections are also used to provide mechanical support. You may use epoxy if additional reinforcement is necessary. Figures 1, 2 and 3 show the typical mounting methods for each part type. The recommended attachment technique for each style is shown in Table 1. Table 1 W1 WB1 W3* Term Ground Term Ground Term Ground Epoxy X X X X Wire Bond Preform X X Tabs X Paste X X X X X Pretinned X X X * For maximum performance and reliability, W3 style parts should be mounted with film side down. When choosing an attachment technique, the primary concern is to achieve the desired RF performance. The W1, WB1 and W3 designs have been optimized for best performance when mounted according to the above guidelines. The most common use for these devices is on a 50 Ohm microstrip transmission line. RF performance will vary with the ground plane spacing under the device, as well as with the dielectric constant of any insulating material. Any device parasitic reactance can usually be compensated with external circuitry. In general, for attenuation values of 1 through 8 db capacitance to ground should be minimized. This can be accomplished by using a thick, low dielectric constant ground plane spacing. For values of 8 db and higher, the best performance is achieved when the device sits directly on ground. In all cases, grounding is critical. If the device is surface mounted, you must provide plated thru-holes in close proximity to the topside ground pad. Make the input and output termination connections with a low inductance bond. The W3 terminations produce such a bond simply by the design of the wraparound metallization. The W1 terminations are usually connected to the substrate using small tabs or wires. The width of the tab should be equal to the smaller of either the substrate line width or the chip pad size. The WB1 has wire bondable terminations. We recommend a low inductance ribbon bond or multiple wire bonds. continued on next page 66

14 Wrapped Chip Device Mounting Instructions (continued) Part Preparation Prior to mounting, both the parts and the mounting surfaces must be free of any impurities that may interfere with the attachment process. Common contaminants include finger oils, surface oxides and organic compounds associated with component processing and packaging. Epoxy You may use epoxy bonding for most applications, but be aware that its most serious drawback is outgassing. When used in a sealed package, epoxy outgassing may contaminate other parts. We recommend silver conductive epoxies for RF applications. Solvent-free epoxies, such as Ablestik 84-1LMI or EPO-Tek H20E, are acceptable. The epoxy may be either screened or dispensed onto the substrate surface before setting the part on the board. Be sure that an epoxy fillet is visible to verify full coverage. For surface mounting the W3, minimize the epoxy under the chip to prevent spreading which could cause degraded performance or an unwanted connection between pads. Adding epoxy to the edge of the W3 will improve the electrical contact and add mechanical support. Epoxy preforms may be used for the ground planes of the W1 and WB1. Ablestik ECF564A is a suitable conductive film adhesive. When using an epoxy preform, clamp the part in place with a spring clip or a weight to ensure that the preform adheres to both surfaces. Soldering and Circuit Board Considerations Success when soldering surface mount components depends upon the soldering surface. The size and location of the solder pads is critical. Provide a pad that is 0.010" to 0.020" over the termination size 1. Center the pad along the axis of the chip and bias it slightly from each end to allow for a solder fillet. Isolate the pads from the connecting lines to prevent solder wicking. Use either insulating solder dams over the conductors or narrow traces off the pads to assist in solder fillet formation. Failure to follow these guidelines can lead to component skewing and/or tombstoning ➁ (draw bridging). Figure 4 illustrates common pad design problems and solutions. Figure 5 and Figure 6 may be used as circuit board layout guidelines for TS0300W3 and TS0500W3 attenuators, respectively. For highest reliability, W3 components are best mounted with the attenuator film facing the circuit board. When mounted in this manner, the three terminations which make direct contact to the film also make contact to the traces on the circuit board. Six of the nine terminations of the W3 can be damaged without producing an electrical failure if the part is mounted with the film side down. The W1 and WB1 components have full back metallizations, and may therefore be subject to skewing. On the W3 parts, the pads on the underside of the part are designed to minimize the possibility of tombstoning. Pad size can help minimize tombstoning in two ways. First, by making the pad areas equal, the force from the surface tension of the liquid solder on the three pads will be equal. Second, since the chip is tipped by the lifting moment produced by the solder fillet, the smaller the chip height to pad width ratio is, the smaller will be the resulting lifting force. With the W3, the input and output pads are equal in area. This produces equal forces from front to back. The ground pad is slightly larger than the input and output pads, therefore the side-to-side forces on the chip are equalized. Also, for both the TS0300 and TS0500, the largest height to width ratio is 0.75". Since this part exhibits little affinity for tombstoning, the ratio of 0.75" is a good guideline ➂. Flux Flux is a solution used to clean the metal surfaces and remove any oxides prior to soldering. Consult with your solder supplier to determine the best process for your assembly application. EMC chip devices are designed to perform in all solder assembly processes. continued on next page 67

15 Wrapped Chip Device Mounting Instructions (continued) Preforms Preforms are solid sheets of solder, available with or without flux, that are used primarily for soldering large ground plane areas. Set the preform on a prefluxed surface with the chip positioned over it. Hold the chip in the proper position during reflow with a non-solder wetting jig (e.g., Vespel, stainless steel, aluminum, etc.). Apply pressure to the top of the chip to prevent any trapped air from causing the part to tip or allowing gaps to form. The scrubbing action of a die bonder can prevent both. Die bonding is commonly performed using a heated stage with the reflow heat produced by a hot air torch or an infrared (IR) lamp. You may also solder the chip using a hot plate or a furnace reflow technique. Set the soldering schedule to minimize the duration and intensity of the part exposure to high temperatures. Limit the time on the hot plate to 3 minutes if you are using a good thermally conductive and moderate thermal mass fixture. A short soldering time interval will prevent flux burning and reduce the amount of brittle intermetallic compound formation in the solder joint. To ensure the formation of the proper solder fillet, select a preform size that is 0.005" to 0.010" larger than the size of the solder pad. Sn 62 Pb 36 Ag 2 solder (178 C eutectic) is recommended for all soldering operations, however, soldering temperatures of 250 C for 30 seconds will not damage the parts. Reference 4 gives appropriate furnace profiles for different solder materials. Solder Paste Solder paste is a solution of solder, flux, and solvents. Other materials are often added to optimize the screening or dispensing operation. Drying the paste slightly prior to soldering will eliminate any solvents that might boil and cause solder splashes. However, care must be taken not to dry out the flux completely. When large areas must be pasted, screening is the preferred method because it provides an even and repeatable deposition. Deposit the paste onto the substrate either by dispensing or screening. Next, place the chips on the pasted areas. The tackiness of the paste will hold the surface mounted components in place. Next, flow the parts by heating the substrate up to the soldering temperature. Starting with a preheating stage will help reduce the thermal shock to both the parts and the substrate. Follow the preheating with a second-stage heating up to the soldering temperature using an IR, soldering iron, flame, hot air torch, or with a furnace. Pretinning Pretinning is the solder coating of the component and/or the substrate prior to soldering the two together. This is most often accomplished by dipping the parts in a pot of molten solder. You can pretin the substrate by plating during fabrication, or by depositing and reflowing solder paste. Remove excess solder with a squeegee wipe. Then follow the pasted reflow techniques described in the Solder Paste section above to solder the parts. Be particularly careful when pretinning these extremely small parts. Tabs You can connect the input and output terminations of the W1 to the substrate with pretinned or gold plated soft copper tabs. We suggest that you attach the tabs to the part using a high temperature solder (Sn 96.5 Ag 3.5, 220 C eutectic) and then join the tabs to the substrate using a standard Sn 62 (178 C eutectic). If higher temperature solders can t be used, solder the tabs by preheating the whole assembly to between 20 and 30 C below the soldering temperature. Then add heat to one side of the tab at a time. Cleaning After soldering, clean the substrate to remove any flux or residual solvents. Ultrasonic cleaning followed by a solvent rinse is the most common method. Most flux manufacturers will also supply effective flux solvents. continued on next page 68

16 Wrapped Chip Device Mounting Instructions (continued) Wire Bonding EMC supplies WB1 attenuators with gold terminations for wire and ribbon bonding. Thermal compression and ultrasonic wedge and ball bonding are the most common bonding methods. First, attach the chip to the substrate with epoxy or solder. Heat the substrate to about 150 C. A gold metallic bond will form between the wire and the bonding pad by adding thermal and/or ultrasonic energy while compressing them together. As with the soldering operation, clean all surfaces prior to bonding, as described in the Part Preparation section. Figure 1 Figure 2 Figure 3 continued on next page 69

17 Wrapped Chip Device Mounting Instructions (continued) Figure 4 Figure 5 Figure 6 References ➀ Erickson, David. How to Design for Manufacturability. Surface Mount Technology. February ➁ Giordano, Jerry and David Khoe. Chip Resistor Design Helps Prevent Tombstoning. Surface Mount Technology, August ➂ Harper, Charles A. Handbook of Thick Film Hybrid Microelectronics. McGraw Hill, Inc., ➃ Manko, Howard H. Solders and Soldering. McGraw Hill, Inc.,