Application Notes Introduction EMC Technology has provided an

Application Notes
Introduction
EMC Technology has provided an
extensive collection of Application
Notes that help designers mount and
measure the products. These
Application Notes 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................................................................................76
EMC Technology 8851 SW Old Kansas Ave. Stuart FL 34997 (772) 286-9300 (800) 544-5594 www.emct.com
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Thermopad® Amplifier Temperature
Compensation
Application Notes
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 -0.001 dB/°C for every dB of gain. So a 30 dB amplifier
would have a gain coefficient of -0.03 dB/°C. The gain of the amplifier can be stabilized over temperature by
cascading it with a 6 dB Thermopad with a -0.03 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
EMC Technology 8851 SW Old Kansas Ave. Stuart FL 34997 (772) 286-9300 (800) 544-5594 www.emct.com
59
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Thermopad® Attenuation Shift
Due to Self Heating
Application Notes
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 -0.06 dB. Even when operated at full rated power,
attenuation shift of the Thermopad due to self-heating is minimal.
EMC Technology 8851 SW Old Kansas Ave. Stuart FL 34997 (772) 286-9300 (800) 544-5594 www.emct.com
60
A Smiths Group company
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Chip Device Mounting Instructions
Application Notes
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
Termination
Type
Planar
Pretinned
(S)
Gold
(G)
Three Tabs*
(T3)
Two Tabs*
(T2)
One Tab*
(T)
Wraparound
Ground (M)
Epoxy
Term
Ground
Term
Ground
Term
Ground
Term
Ground
Term
Ground
Term
Ground
Term
Ground
Wire or
Die Bond
X
X
Solder
Preform
Solder
Paste
X
X
X
X
X
X
Pretinned
Solder
Reflow
Rosin
Core Wire
Solder
Flip Chip
(Figure 1)
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
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
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61
A Smiths Group company
Chip Device Mounting Instructions
(continued)
Application Notes
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
EMC Technology 8851 SW Old Kansas Ave. Stuart FL 34997 (772) 286-9300 (800) 544-5594 www.emct.com
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Chip Device Mounting Instructions
(continued)
Application Notes
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 3.5 220°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
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63
A Smiths Group company
Chip Device Mounting Instructions
(continued)
Application Notes
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
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Chip Device Mounting Instructions
(continued)
Figure 4
Application Notes
Figure 5
References
➀ Erickson, David. “How to Design for Manufacturability.” Surface Mount Technology. February 1989.
➁ Giordano, Jerry and David Khoe. “Chip Resistor Design Helps Prevent Tombstoning.” Surface Mount Technology.
August 1988.
➂ Manko, Howard H. Solders and Soldering. McGraw Hill, Inc., 1992.
EMC Technology 8851 SW Old Kansas Ave. Stuart FL 34997 (772) 286-9300 (800) 544-5594 www.emct.com
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Wrapped Chip Device Mounting
Instructions
Application Notes
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
Term
Epoxy
WB1
Ground
Term
X
Wire Bond
W3*
Ground
Term
Ground
X
X
X
X
X
X
X
X
Preform
Tabs
X
Paste
X
X
X
X
X
Pretinned
* 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
EMC Technology 8851 SW Old Kansas Ave. Stuart FL 34997 (772) 286-9300 (800) 544-5594 www.emct.com
66
A Smiths Group company
Wrapped Chip Device Mounting
Instructions (continued)
Application Notes
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
EMC Technology 8851 SW Old Kansas Ave. Stuart FL 34997 (772) 286-9300 (800) 544-5594 www.emct.com
67
A Smiths Group company
Wrapped Chip Device Mounting
Instructions (continued)
Application Notes
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
EMC Technology 8851 SW Old Kansas Ave. Stuart FL 34997 (772) 286-9300 (800) 544-5594 www.emct.com
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Wrapped Chip Device Mounting
Instructions (continued)
Application Notes
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
EMC Technology 8851 SW Old Kansas Ave. Stuart FL 34997 (772) 286-9300 (800) 544-5594 www.emct.com
69
A Smiths Group company
Wrapped Chip Device Mounting
Instructions (continued)
Figure 4
Application Notes
Figure 5
Figure 6
References
➀ Erickson, David. “How to Design for Manufacturability.” Surface Mount Technology. February 1989.
➁ Giordano, Jerry and David Khoe. “Chip Resistor Design Helps Prevent Tombstoning.” Surface Mount Technology,
August 1988.
➂ Harper, Charles A. Handbook of Thick Film Hybrid Microelectronics. McGraw Hill, Inc., 1974.
➃ Manko, Howard H. Solders and Soldering. McGraw Hill, Inc., 1992.
EMC Technology 8851 SW Old Kansas Ave. Stuart FL 34997 (772) 286-9300 (800) 544-5594 www.emct.com
70
A Smiths Group company