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The content may not be copied in whole or part without the prior written permission of an authorised officer of DEK.

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The content of this presentation is confidential and the copyright of DEK. It is intended for the exclusive use of the recipient.

The content may not be copied in whole or part without the prior written permission of an authorised officer of DEK.

Thank you!

Area Ratio Calculator For Rectangular aperturesAperture Width Aperture Length Foil Thickness Ratio

7.24 6.53 3 0.572224642947.2772 27.54

82.62

Area Ratio Calculator for Circular AperturesAperture Diameter Foil Thickness Ratio

9.4 4 0.58754.7 118.1238837904

22.0969.39778172686

Industry Standards Aspect Ratio Foil Selection Area Ratio FormulaMinimum webPb-Free Design Ind. Std. Calculator Reduction in X & Y

Reduction of Area

Helps for determining the correct aperture design

Aperture Width

Aperture Length

Foil Thickness

B19

For Standard Pb-rich solder, all apertures should be reduced so that they are not 1:1 to the pad footprint. All passive components: ie chip resistors, Sot23’s, Tant Caps, IC’s above 50 mil (1.27mm) pitch a reduction of 2 mil (50μ) per edge should be applied. For most leaded components the aperture width should equal ½ the component pitch, and the length should be reduced typically 2 mil per edge.

C19

A well known and accepted rule of thumb states that Solder paste will release satisfactorily from the stencil Aperture if it’s width is not less that the stencil thickness x 1.5. This is also commonly called the Aspect Ratio. Area ratio calculations should be combined with aspect ratio calculations to determine the best choice for aperture modifications.

D19

Typically the smallest component pitch should always dictate the foil thickness. Smallest Component Pitch Recommended Foil Thickness 50 mil (1.27mm) 8 mil (200μ) 40 mil (1.02mm) 8 mil (200μ) 32 mil (0.8mm) 8 mil (200μ) 25 mil (0.635) 6 mil (150μ) 20 mil (0.5mm) 6 mil (150μ) 16 mil (0.4mm) 5 mil (125μ) 12 mil (0.3mm) 4 mil (100μ)

E19

For Rectangular Apertures. The Area of aperture opening divided by the area of aperture wall equals the area ratio. L x W = >0.66 2 x (L + W) x t L = aperture length W = aperture width t = thickness of stencil For Circular Apertures. The area of the aperture opening divided by the area of the aperture wall equals the area ratio. πR² . = >0.66 2πRt = D/4t

C20

As a standard rule, the minimum web between apertures should be 1:1 to the foil thickness. For example a 6 mil thick stencil should have a web between apertures of no less than 6 mils.

When considering the printability of a stencil design, the Area Ratio for optimum paste release should be >0.66.

To use this calculator, simply enter the values in the rows indicated by the red arrow, and enter. The area ratio will display in the yellow cell.

Substrate

Area Ratio = Wall Surface Area

Aperture Open Area

Next

Ind. Stds ReductionsThis Calculator represents Industry Standard ReductionsEnter the pad pitch, pad width, Land Pattern Sizeand pad length under Land Pattern Size. Under Stencil Design enter the Foil Pad PitchThickness, and the 25recommended aperturesize will be shown with the area ratio. Pad

Length60

PadWidth

14

Solder Volume 1:1 with pad footprint 5040Solder Volume with Ind. Std Reduction 4350

Return to Area Ratio Page

Ind. Stds Reductions = 690 cubic mil of solder

Stencil Design

FoilThickness 6

ApertureLength

58

Aperture 12.5Width

Area Ratio 0.856974

725846


Next

This Calculator represents reductions Percentage of area reductionin total area. 20 0.20 0.80 20

0.894427

Enter the pad pitch, pad width, Land Pattern Sizeand pad length under Land Pattern Size. Under Stencil Design enter the Foil Pad PitchThickness. Enter the 20desired percentageof area reduction. Aperture size with Padarea ratio will be Lengthshown. 65

PadWidth

10

Solder Volume Without Reduction Solder Volume With Reduction

2 13

520 0.77517134.1641 670.8204


Next

Percent Reduction = 650 cubic mil of solder

Stencil Design

FoilThickness 5

ApertureLength58.13777

Area Ratio0.77517

Aperture 8.9442719Width

Solder Volume Without Reduction 3250 Solder Volume With Reduction 2600

520 520 5 650670.82039


This Calculator represents reductions Percentage of reductionin X and Y. 12 12

Enter the pad pitch, pad width, Land Pattern Sizeand pad length under Land Pattern Size. Under Stencil Design enter the Foil Pad PitchThickness. Enter the 20desired percentageof reduction in X & Y. Aperture size with Padarea ratio will be Lengthshown. 50

PadWidth

12

Solder Volume Without Reduction Solder Volume With Reduction

1.44 6

464.64 0.709677109.12 654.72


Next

Percent Reduction = 812.16 cubic mil of solder

Stencil Design

FoilThickness 6

ApertureLength

44

Area Ratio0.709677

Aperture 10.56Width

Solder Volume Without Reduction 3600 Solder Volume With Reduction 2787.84

464.64 464.64 6 600654.72



Pb-Free Stencil Design

Typical SMT stencil design for lead rich solder reduces the stencil aperture so that the paste brick is not 1:1 to the pad footprint. The Stencil aperture is reduced 1-3 mils per side depending on the pad size and pitch.

Paste Brick

Pad Footprint

Pb-Free aperture design is closer to a 1:1 to the pad footprint, with a minimal reduction. The reason for this is the wetting characteristics for Pb-free solder will, in most cases, not allow the typical and familiar reductions since the migration of molten solder, and capillary action are less robust than with Pb-rich solder.

Pb-Free Stencil Design

Typical SMT stencil design for lead rich solder reduces the stencil aperture so that the paste brick is not 1:1 to the pad footprint. The Stencil aperture is reduced 1-3 mils per side depending on the pad size and pitch.

1-3 mil reductionper side is typical.

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