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Ceramic Surface Mount

Mounting Pad

Dimensions and Considerations

The objective of this document is to introduce the IPC-SM-782 methodology for

solder reflow land patterns. The methodology will be extended to all NOVACAP

standard and non-standard part sizes including assumptions for pick & place

accuracy along with desired solder fillets. NOVACAP strongly recommends the

user review the IPC-SM-782 document and visit their web site at

www.ipc.org

We remind the user they are responsible for all additional modifications needed

for solder fillet visual requirements and level of robustness.

The amount of solder applied to the chip capacitor will influence the reliability of

the device. Excessive solder can create thermal and tensile stresses on the

component that could lead to fracturing of the chip or the solder joint itself.

Insufficient or uneven solder application can result in weak bonds, rotation of the

device off line or lifting of one terminal off the pad (tombstoning).

The volume of solder is process and board pad size dependent. The following

pad sizes are represented for solder reflow and vapor phase processes. WAVE

SOLDERING exposes the devices to a large solder volume, hence the pad size

area must be restricted to accept an amount of solder that is not detrimental to

the chip size utilized. Typically the pad width is 66% of the component width, and

the length is .030 (.760 mm) longer than the termination band on the chip. A

0805 chip, which is .050 wide and has a .020 termination band, therefore

requires a pad .033 wide by .050 in length. Opposing pads should be identical in

size to preclude uneven solder fillets and mismatched surface tension forces,

which can misalign the device. It is preferred that the pad layout results in

alignment of the long axis of the chips at right angles to the solder wave, to

promote even wetting of all terminals. Orientation of components in line with the

board travel direction may require dual waves with solder turbulence to preclude

cold solder

25111

joints on the trailing terminals of the devices, as these are blocked from full

exposure to the solder by the body of the capacitor. Restrictions in chip

alignment do not apply to SOLDER REFLOW or VAPOR PHASE processes,

where the solder volume is controlled by the solder paste deposition on the

circuit pads. Pads are designed to match or slightly exceed the width of the

capacitor, with length .030 (.760 mm) greater than the chip terminal band width,

to provide a wetting area for a full solder fillet.

Most of the ceramic surface mount capacitors may not be wave soldered. The

0402 size capacitors will likely experience solder bridging due to the close

proximity of the terminations. The 0603 can be wave soldered however the glue

dots must be accurately placed and the wave controlled to prevent bridging.

Ceramic capacitors larger than 1210 should not be wave soldered. Large

thermal gradients are present as well as robustness issues due to board flex

problems. Some design layouts have required wave soldering of the 1812 size.

This should be done with extreme caution.

There are practical limitations on capacitor sizes that prohibit reliable direct

mounting of chip capacitors larger than 2225 to a substrate. Without mechanical

restriction, thermally induced stresses are released once the capacitor attains a

steady state condition, at any given temperature. Capacitors bonded to

substrates, however, will retain some stress, due primarily to the mismatch of

expansion of the component to the substrate; the residual stress on the chip is

also influenced by the ductility and hence the ability of the bonding medium to

relieve the stress. Unfortunately, the thermal expansions of chip capacitors differ

significantly from those of substrate materials. At 25°C to 300°C, capacitors

typically range in expansion coefficient from 8.3 x 10

-6

to 12.2 x 10

-6

in/in/°C,

while 99% Alumina is approximately 6.0 x 10

-6

in/in/°C and P.C. board is typically

16.0 x 10

-6

in/in/°C.

The IPC-SM-782 formulas and calculation were adopted to determine the pad

sizes for the “J” and “L” leaded configurations. An industry standard does not

exist for these leaded configurations. The tab dimension and tolerances

replacing the endband numbers determined the dimensions. The capacitor

thickness range was remained constant at .010”-.070” for the toe, heel, and side

solder fillet calculations.

All statements, information and data given within this document are believed to

be accurate and reliable, but are presented without guarantee, warranty, or

responsibility of any kind, expressed or implied. Specifications are typical and

may not apply to all applications.

Footprint Design For Surface Mount Capacitors

B B

SIZE

Width

Pad

Spacing

Length

0402

0.028

0.035

0.018

0.088

0403

0.038

0.035

0.018

0.088

0504

0.048

0.036

0.026

0.098

0603

0.038

0.040

0.030

0.110

0805

0.060

0.045

0.035

0.125

1005

0.060

0.055

0.040

0.150

1206

0.068

0.065

0.045

0.175

1209

0.100

0.065

0.045

0.175

1210

0.110

0.065

0.045

0.175

1515

0.165

0.070

0.060

0.200

1808

0.090

0.075

0.080

0.230

1812

0.135

0.075

0.080

0.230

1825

0.265

0.075

0.080

0.230

2020

0.215

0.075

0.100

0.250

2211

0.120

0.085

0.105

0.275

2215

0.160

0.085

0.105

0.275

2221

0.225

0.085

0.105

0.275

2225

0.265

0.085

0.105

0.275

Footprint Design For Large Surface Mount Capacitors

(NOVACAP does not recommend direct mounting of chip capacitors larger

than 2225 to a substrate. Pad sizes are presented to satisfy requests. Care

must be taken in use for differences of thermal expansion.)

                                                      D

               A




                                                      C
                                  B                                     B

SIZE

Width

Pad

Spacing

Length

2520

0.215 0.085 0.130 0.300

3030

0.315 0.085 0.180 0.350

3040

0.420 0.085 0.180 0.350

3333

0.350 0.090 0.210 0.390

3520

0.215 0.090 0.230 0.410

3530

0.315 0.090 0.230 0.410

3540

0.420 0.090 0.230 0.410

3545

0.475 0.090 0.230 0.410

3640

0.420 0.090 0.240 0.420

4020

0.215 0.105 0.250 0.460

4040

0.420 0.105 0.250 0.460

4540

0.420 0.105 0.300 0.510

5040

0.420 0.110 0.345 0.565

5440

0.420 0.110 0.390 0.610

5550

0.525 0.110 0.400 0.620

6560

0.630 0.115 0.490 0.720

7565

0.685 0.120 0.590 0.830

Footprint Design for “J” leaded Capacitors

.100” Typ. .040” Typ

C D

Size

# Leads

1812

0.100

0.050

0.250

1825

0.100

0.050

0.250

2020

0.100

0.070

0.270

2221

0.105

0.085

0.295

2225

0.105

0.085

0.295

2520

0.105

0.115

0.325

3030

0.105

0.165

0.375

3040

0.105

0.165

0.375

3333

0.110

0.185

0.405

3520

0.110

0.205

0.425

3530

0.110

0.205

0.425

3540

0.110

0.205

0.425

3545

0.110

0.205

0.425

3640

0.110

0.215

0.435

4020

0.110

0.260

0.480

4040

0.110

0.260

0.480

4540

0.115

0.300

0.530

5040

0.115

0.355

0.585

5440

0.115

0.395

0.625

5550

0.120

0.395

0.635

6560

0.120

0.500

0.740

7565

0.125

0.595

0.845

Footprint Design for “L” leaded Capacitors

.100” Typ. .040” Typ

C D

Size

# Leads

1812

0.100

0.150

0.350

1825

0.100

0.150

0.350

2020

0.100

0.170

0.370

2221

0.105

0.185

0.395

2225

0.105

0.185

0.395

2520

0.105

0.215

0.425

3030

0.105

0.265

0.475

3040

0.105

0.265

0.475

3333

0.110

0.285

0.505

3520

0.110

0.305

0.525

3530

0.110

0.305

0.525

3540

0.110

0.305

0.525

3545

0.110

0.305

0.525

3640

0.110

0.315

0.535

4020

0.110

0.360

0.580

4040

0.110

0.360

0.580

4540

0.115

0.400

0.630

5040

0.115

0.455

0.685

5440

0.115

0.495

0.725

5550

0.120

0.495

0.735

6560

0.120

0.600

0.840

7565

0.125

0.695

0.945