Solder paste stencils

Solder paste stencils bruce Thu, 07/29/2010 - 09:01

A solder paste stencil is used to apply solder paste to the surface mount pads of a PCB. Typically, a stencil is stretched over the PCB so that the correct quantity of solder paste may be placed on each pad. The amount of solder paste is a function of the stencil opening size and the stencil thickness. Often, openings in the stencil are reduced, relative to the copper pad size, by some percentage so that the correct amount of solder paste will be applied to the pads.

You can use the Stencil Module to create solder paste stencil product(s) either by extracting the paste mask data from an existing PCB product, or by importing the data from a Gerber file.

Graphic display

The graphic region displays the stencil. The check boxes in the layer list control which layers are visible.

See the Product browser chapter for an overview of viewer functionality such as pan and zoom, display modes, mirrored and rotated view, and measurement.

Select and modify operations

Use the left mouse button to draw a selection rectangle around the openings to select. Only openings on the chosen layer are selected. There are five selection modes:

  • Select selects all of the openings within the selection rectangle. All openings outside the rectangle are deselected.
  • Select similar selects all of the openings that have the same aperture definition (D-code) as the selected opening. All other openings are deselected. You may only select one opening.
  • Selection add selects all of the openings within the selection rectangle without deselecting any previously selected openings.
  • Selection subtract deselects only the openings within the selection rectangle, leaving the remaining openings selected.
  • Selection clear deselects all selected openings.

Panelized products

When working with a regular array of a single product which has been created by the Macaos Panel Module, then the lower left board in the panel will be highlighted with a yellow rectangle. In most cases, an action performed within the yellow rectangle will automatically be duplicated to all of the other boards in the array.

This applies to the following actions:

  • Shape manipulation: Selective adjustment of opening size
  • Fiducials: Manual fiducial selection
  • Split or edit openings
  • Edit shapes width/height
  • Delete objects
  • Reduced thickness (stepped) regions
  • Transfer objects from other layers

Creating stencil products

Use the following procedure to create a solder paste stencil:

  1. Locate the PCB product. Select the product in the Macaos Enterprise product browser and then click on the Stencil button to open the Stencil module.

    If you wish to create a stencil product directly from Gerber and/or DXF files, then click on a folder name (so that no product is selected) before clicking on the Stencil button.

  2. Run an Autostencil script (optional). If deisred, select a script from the Autostencil menu. After running the script, skip to step 7. See the Autostencil section for more info.

  3. Specify side(s), frame and stencil properties. Use the Stencil and frame data design action to specify the side(s) to use for the stencil, select a frame and specify stencil properties.

  4. Specify board placement. Use the Placement design action to specify the placement of the data within the frame.

  5. Adjust the size of openings. Use the Shape manipulation design action to specify opening size adjustments and corner rounding.

  6. Define fiducial marks (optional). Use the Fiducials design action to detect or define fiducials marks.

  7. Modify the shape of openings (optional). Use the Split openings design action to modify the shape of an opening or to break a large opening into a pattern of smaller openings.

  8. Add text to the stencil (optional). Use the Text design action to specify the product's name and description, and place text (if desired).

  9. Delete unnecessary objects (optional). Use the Delete objects design action to delete any unnecessary objects from the stencil data.

  10. Create stepped regions (optional). Use the Reduced thickness regions design action to define regions of the stencil that should be thinner than the rest of the stencil.

  11. Extract data from other layers (optional). Use the Transfer objects design action to copy objects from any other layer to a stencil layer.

  12. Publish the stencil product. Click on the Publish stencil button to create the new paste mask stencil product(s). By default, a stencil product is created with the same product number as the PCB product, plus pt (for top) or pb (for bottom) or just p (for both). If the paste mask product already exists, then the new product will be given a new product number (plus pt, pb or p).

Stencil and frame data

Stencil and frame data bruce Wed, 07/25/2018 - 08:41

The check boxes at the top of the panel specify the layer(s) for which stencils will be created.

If no product has been selected, then the Load buttons may be used to import Gerber or DXF data for the stencil(s) to create. The Load top and Load bottom buttons import the stencil opening data for the top and bottom layers respectively. The Load outline button may be used to load a board outline for use when centering in the stencil frame. Note: Only limited import of DXF data is supported. DXF entities that do not easily map to Gerber-style objects are ignored.

Select frame

Select a frame for the stencil product. You may choose from one of the active frames in the list or define your own frame using the Frame Manager.

Alternatively, a frame may be generated from product data in the following manner:

  1. Click on the Select from data button (so that it is down)

  2. Select a layer that contains the stencil frame outline. Note: Only visible layers are listed.

  3. Draw a selection rectangle around some portion of the outline.

Note: The frame outline must be a closed polygon outline (a closed end-to-end chain of line segments without gaps or overlap). If necessary, use the Delete frame button to delete the frame.

If desired, use the Rotate frame button to rotate the frame relative to the board data.

Stencil specifications

The stencil size is normally determined by the selected frame. If no frame is selected then it must be specified.

The stencil thickness is normally determined by the selected frame. If desired, this may be changed as needed. If no frame is selected then a thickness must be chosen. The recommended maximum stencil thickness is calculated from the Aspect ratio and Area ratio of the smallest stencil apertures.

The stencil type is normally determined by the selected frame. All types other than Normal are licensed or patented frame patterns that are usually related to specific frame sizes.

Set a check mark by the Coated option if the stencil should be coated (e.g. nano-coating) to improve hole wall smoothness and paste release. The actual coating process may vary from supplier to supplier. This is an extra cost option.

Set a check mark by the Polish option if the walls of stencil openings should be electro-polished, to improve smoothness. This is usually a standard option, but may incur an extra cost with some suppliers.

Set a check mark by the Protect frame option if the frame edges are to be protected (typically to help operators avoid cutting their hands on the stencil edges). For normal stencil types, this would typically be folding the frame edges back. For some stencil types there are more advanced protection methods, such as the LPKF Protect System.

Placement

Placement bruce Wed, 07/25/2018 - 08:42

The stencil data may either be placed relative to the center of the frame or the frame edge.

If there is solder paste data for both sides of the board, then you may choose to include openings for both sides of the board on the same stencil by marking the Place top and bottom data on one stencil check box. You may also choose to add text indicating which set of openings applies to which side of the PCB.

If you do not choose to place top and bottom data on one stencil, then two stencil products will be created when you publish. When creating two stencils, you may choose either to place the data at the same location on each stencil, or specify individual locations for the top and bottom data. If individual locations are chosen, then you may choose to separate the two sides either horizontally or vertically. Use the Swap left/right data position check box to swap the positions of the two layers.

If the data is placed relative to the center of the frame, then an offset may be specified. You may also choose between anchoring the data either to the center of the board outline or the center of the solder paste openings. If top and bottom data is specified with individual locations, then you should specify the distance between the two boards.

If the data is placed relative to the frame edge, then you must specify offsets. You may choose either to specify offset from the frame edge to the farthest board edge or from the frame edge to the nearest board edge. (If there is data for both sides of the board, then there will be two offsets, one from each edge of the frame.)

Normally, the bottom side data will be mirrored so that the bottom side of the stencil will be in contact with the board, regardless of which side of the board will have solder paste applied. This may be disabled by unmarking the Mirror bottom data check box. You may also choose between horizontal and vertical mirroring.

Shape manipulation

Shape manipulation bruce Wed, 07/25/2018 - 08:43

Opening size adjustment

Stencil openings are adjusted as a percentage (by area) of the reference pad size. The reference pad is either the copper layer pad or the original paste mask data pad, depending on the selected Adjustment reference.

Specify the desired percentage prior to executing an adjustment operation. A negative percentage results in an opening that is smaller than the reference pad. Repeated opening adjustments are not cumulative.

You should first adjust all openings to the adjusted size that applies to the majority of openings. Then you may re-adjust individual openings by selecting them and applying the desired adjustment.

To adjust openings, specify the percentage, select Adjust all, Adjust selected top or Adjust selected bottom and then click on the Apply button.

Use the left mouse button to draw a selection rectangle around the openings to select. Only openings on the chosen layer are selected. The selection modes are described in the Graphic display section.

To undo all adjustments, adjust all openings to 0%.

Show Adjustments

As each opening size adjustment is carried out, the operation is added to the list of adjustments. Clicking on a row in the list causes all openings with the selected adjustment to be highlighted in the graphic display.

Corner rounding

Specify the desired radius for the corners of rectangular openings. You should specify a radius approximately equal to the radius of the solder grains in the solder paste.

Potential errors

Opening sizes are compared with the original paste mask layers for potential errors, such as openings that were already reduced in the original data or openings where the reference copper pad was not found. If a Potential errors button is enabled, click on the button and inspect the highlighted openings to see if there are any actual errors.

Fiducials

Fiducials bruce Wed, 07/25/2018 - 08:44

If the paste mask data includes fiducial marks, these should be selected and marked as fiducials. Fiducial marks are etched into the stencil rather than being cut all the way through.

Manual fiducial selection

Choose a layer and click the Select fiducials button (so that it is down). Use the left mouse button to draw a selection rectangle around the openings to select. Only objects on the chosen layer are selected. The selection modes are described in the Graphic display section.

All highlighted objects will be treated as fiducials when the production data is generated. Note: If a copper layer is chosen, then the selected fiducials will be copied from the copper layer to the stencil.

Assumed and panel fiducials

Assumed fiducials are round objects in the paste mask data with a diameter between 0.8 mm and 1.2 mm. If any such objects are found on a layer, the corresponding button is enabled.

Panel frame fiducials are stencil fiducials that were defined in the Panel module. If any such fiducials are defined for a layer, the corresponding button is enabled.

Clicking on a Show fiducials button highlights the fiducials and opens a menu with 3 or 4 options:

  • Set all to fiducials marks all highlighted objects to be etched rather than cut.

  • Delete all removes all highlighted objects from the stencil data

  • Cut as normal holes marks all highlighted objects to be cut rather than etched.

  • Edit the selection (Assumed fiducials only) lets you select which objects are highlighted.

If Warn for possible fiducials is checked, a warning will be generated if any assumed fiducials (that are not marked as fiducials) are found in the stencil data when publishing.

Split or edit openings

Split or edit openings bruce Wed, 07/25/2018 - 08:45

Often it is desirable to split a large stencil opening into an array of smaller openings. This can give better control over the total amount of solder paste deposited on a large pad.

Choose a layer and then use the left mouse button to draw a selection rectangle around the opening to split. (You may only select one opening.) Only openings on the chosen layer are selected. The selection modes are described in the Graphic display section.

You can use the Highlight large pads button to help you locate pads that should be split. All pads whose width and height are larger than the Min size value will be highlighted.

Note: You may select only one opening to edit. If you select more than one pad, or if an opening is made up of several overlapping graphic objects, then you may choose to treat the selected objects as a single rectangle surrounding all selected objects. In such cases, it may afterwards be necessary to delete some of the small openings created by the split operation.

Once the desired openings have been selected, click on the Split or replace openings button to open the Split or replace stencil opening editor. The un-split opening is shown in red and the new openings are shown in magenta.

Note: The red opening is the un-split opening size, not the copper pad size.

You may choose between several options to split or replace the pad. For each New shape type you may specify the size and placement of the replacement openings to meet your specific needs.

The Original opening and New opening(s) statistics calculate how your proposed changes will affect the opening size (and thereby the amount of solder paste) for the pad.

Once you are satisfied, click on the Replace opening button to replace the selected opening(s).

Edit shapes width/height

If necessary, the height and width of individual stencil openings may be adjusted.

Choose a layer and then use the left mouse button to draw a selection rectangle around the openings to adjust. Only openings on the chosen layer are selected. The selection modes are described in the Graphic display section.

Specify the desired width and height adjustments as a percentage of the original width/height and then click on the Apply button.

Note: For purposes of this operation, the width is always the shortest dimension of the opening, regardless of whether the “width” is horizontal or vertical. In the same manner the height is always the longest dimension of the opening.

Text and identification

Text and identification bruce Wed, 07/25/2018 - 08:45

Free text

Enter a text and click the Place text button. Click at the desired location on the stencil to place the text. The Clear free text button may be used to remove all free texts.

Frame text

If there is text defined in the stencil frame, Move and Delete buttons may be used to move or delete text from the stencil.

Mark objects as text

If the paste mask data includes text, it should be selected and marked as text. Text is etched into the stencil rather than being cut all the way through.

Choose a layer and click the Mark button (so that it is down) and then select the text objects. All highlighted objects will be treated as text when the production data is generated. In the same manner, use the Unmark button to unmark text objects.

Product identification

By default the stencils are given the same name, article number and description as the PCB product on which they are based, but these may be modified, if desired.

 

Delete objects

Delete objects bruce Wed, 07/25/2018 - 08:46

If the stencil data contains objects that should not be included in the stencil, these should be deleted.

Choose a layer and then use the left mouse button to draw a selection rectangle around the openings to delete. Only openings on the chosen layer are selected. The selection modes are described in the Graphic display section. Click on the Delete selected button to delete the highlighted objects.

If necessary, the Undelete objects button may be used to restore all deleted objects.

 

Reduced thickness (stepped) regions

Reduced thickness (stepped) regions bruce Wed, 07/25/2018 - 08:47

In some cases it may be desirable to “step” a stencil (that is, reduce the thickness of a region of a stencil), in order to better control the amount of solder paste to be applied.

Stencil thickness is reduced in a region by etching the region until the region's thickness has been reduced to the desired thickness. This is done prior to cutting openings in the stencil.

To define reduced thickness regions, specify the side and thickness for the region, select a placement method, click on the Create region button (so that it is down) and then draw (or place) a rectangle on the stencil to define the region.

The region thickness should be defined as the desired thickness for the specified region.

Typically, etching will be done from the squeegee (top) side of the stencil, leaving a flat surface against the PCB. But in some cases, such as when there is a sticker on the PCB, it may be desirable to etch a region from the PCB (bottom) side.

There are three methods for placing a reduced thickness region:

Region by mouse select: Draw a selection rectangle on the stencil to define the region. The region boundaries must be at least 0.5mm from any stencil openings or other regions on the stencil.

Fixed size region: Specify the region dimensions and then place the rectangle where desired.

Region by elements and oversize: Specify an oversize dimension (in mm) and then draw a selection rectangle around the objects to be included in the region.

  • Paste layer: The objects will be selected from the paste mask top or bottom layer

  • Layer in layer list: The objects will be selected from the highlighted layer

  • by boundbox: The region will be created as a rectangle with a clearance of at least the specified oversize dimension from the selected objects on all sides

  • by objects: The region will be the specified oversize dimension larger than the selected objects on all size, following the shape(s) of the selected objects.

To remove a region from the stencil, click on the Remove region button (so that it is in the down position), select the region thickness and then draw a selection rectangle around any portion of the region(s) to remove. Once you have removed the regions you wish to delete, click the Remove region button again to exit delete mode.

Note: Creating reduced thickness regions will increase the cost of the stencil.

Transfer objects from other layers

Transfer objects from other layers bruce Wed, 07/25/2018 - 08:48

Objects may be copied from any other layer to a stencil layer. To do so:

  1. Select the Destination layer (the stencil layer to which the object will be added).

  2. Select a source layer from the list. Note: Only visible layers are listed.

  3. Specify the size of the copy. Choosing 1:1 creates a copy with the same size as the original. Choosing Oversize creates a copy whose height and width are increased as specified.

  4. Use the left mouse button to draw a selection rectangle around the openings to copy. Only openings on the chosen layer are selected. The selection modes are described in the Graphic display section.

  5. Click on the Accept button to copy the selected objects.

The Undo transfers button deletes all objects that have been transferred from other layers.

Component footprints

Component footprints bruce Wed, 07/25/2018 - 08:49

It is possible to modify stencil openings by component footprint. Non-symmetric openings (such as home plate or bow tie shapes) are automatically oriented correctly for pads on each side of the component. This operation can be performed on a single component or on multiple components with the same footprint.

Note: Component footprint editing is only supported for PCBs where test pad data is available. If test pad data (in IPC-D-356 format) was not imported when the product was created, it may be added to the product in the Assembly Data Manager.

 

When an active side is chosen, the paste mask openings are mapped to the test pad data, in order to determine which openings belong to the same component. Based on this, a list of components (grouped by the selected grouping parameters) is displayed.

Select one or more components in a group and click on the Highlight selected components button to zoom to and highlight the components. Then click on the Edit openings button to open the Split or edit stencil openings dialog box. Clicking on the Replace openings button in the dialog box copies the new opening parameters to all openings of all selected components. If the footprint has multiple opening sizes/shapes (or either of the Group options is unchecked) then use the Prev/Next buttons to edit each of the different shapes in the footprint. Note: You can double-click on a group to zoom, highlight and open the editor in a single operation.

Each component in the list has a blue icon, which indicates the type of footprint. Once a component has been edited, it gets a pink icon which indicates the opening shape. Use the Hide edited components check box to exclude components from the list after they have been edited.

If desired, you can locate components by designator with the filter text at the bottom of the list. When the list is filtered, then the Highlight all components in list button will zoom to and highlight all of the components in the filtered list.

Note: Do not confuse test pads with test points or test pins.

  • Test pads are the locations for bare-board testing of the PCB during manufacture, which are extracted from an IPC-D-356 file to the Test pads layers.

  • Test points are specific pads or pins on the PCBA which would be used for in-circuit testing. For each test point, a “component” (with the Test point component class) should be added to the appropriate component layer. Ideally, test points (with TPxx designators) should be included in Pick and Place data, but they may also be created manually.

  • Test pins are the pins in a test fixture which will make contact with the PCBA during in-circuit testing.

Stencil frames

Stencil frames bruce Tue, 10/09/2018 - 14:24

A stencil frame is the Gerber data describing the outer edge, openings and text that should be added to a stencil product. Frames may be annotated with the product number, product name, product article number and/or product owner. In the frame itself, these texts are shown as placeholders. When the frame is used with a stencil product, the product values are substituted into the frame at the specified position.

The first time a stencil is created, the user may choose a generic frame or define a new frame. If a generic frame is chosen, a frame definition will automatically be created for future use.

Stencil Frame Manager

The Stencil Frame Manager lists the frame definitions which are available for use. These frames are available to all users within the same company. The check boxes specify which frames appear in the selection list in the Stencil Product Creator.

To create a new stencil frame, click the Add new button, which opens the Stencil Frame Editor.

To edit an existing frame, select the frame in the list and click the Edit button. This opens the Stencil Frame Editor in Edit mode. In this mode, it is only possible to modify the frame properties.

To delete a frame, select the frame in the list and click the Delete frame button.

Stencil Frame Editor

The Stencil Frame Editor is used to specify the outline, contents and properties of a stencil frame. Once a frame has been created, it will be available for use by anyone in your company.

Frame data

A new stencil frame may be based on a frame template or data from a Gerber file. Macaos Enterprise has several frame templates, which fall into 3 categories:

  • Generic frames define only an outer rectangle and perhaps annotation text

  • Licensed frames are copyrighted frames which are pre-cut by the steel supplier

  • Standard frames are frames for commonly used solder paste application equipment

Choose whether to use a template or a Gerber file. If using a template, select the desired template.

Frame properties

When creating a frame from a Gerber file, the frame size is automatically set to the bounding box of all objects in the Gerber file. Therefore, the Gerber file should not contain any objects outside of the stencil boundary.

When creating a frame based on a generic frame template, the frame size must be specified.

When creating a frame based on any other frame template, the frame size remains unchanged.

A name should be specified for the new frame. In addition, a default thickness and default shape adjustment (% area reduction) may be specified for use when a stencil product using this frame is created.

Frame text

If desired, annotations and text may be added to the frame. Select the texts to add and click on the Place text button (so that it is down) and then click at the position where the lower left corner of the text string is to be placed. If several texts are selected, they will be placed in a left-justified column.

The Clear text button removes all text from the frame.

Once the frame has been defined, click on the Save and Close button to save the frame.

Automatic stencil creation

Automatic stencil creation bruce Tue, 10/09/2018 - 14:26

A solder paste stencil may be automatically created with a script. An autostencil script automatically generates a stencil by selecting the appropriate frame and stencil thickness, board placement, fiducials and stencil opening adjustment as specified in the script. In many cases, a stencil can be generated with one click!

Use the Autostencil|Create script from current settings command to create a script based on the current settings in the Stencil module, for example just after setting up a standard stencil.

The MacaosDemo script is supplied with the program. This script will create a 150 µm stencil with 15% global reduction of stencil openings. To modify this script or create additional scripts, open the script manager.

The available scripts are listed at the top of the left column. Clicking on a script name loads the selected script so that its properties may be viewed or modified. These properties include:

  • Select frame or size: The frame or size of the stencil

  • Stencil thickness: The thickness of the stencil

  • Placement of board within frame: The location of the board on the stencil.

  • Double-sided stencil: Specifies if both board sides should be on one stencil.

  • Mirroring of bottom data: Specifies if and how bottom side data is mirrored.

  • Fiducial detection: Specifies if and how objects in the stencil data should be treated as fiducials rather than openings.

  • Adjustment of stencil openings: Specifies global adjustment of opening sizes and corner radius for stencil openings.

Additional operations (such as adjustment of individual openings, split openings, reduced thickness regions, text operations and deletion of objects) must be carried out after the script has been run.

Use the buttons at the bottom of the Scripts pane save scripts. Right-click in the scripts list to delete, rename, import or export a script. Note: If a stencil script has the same name as a panel script, then a stencil will automatically be created after creating a panel with that script.

Scripts are stored together with the user's program settings. To share a script with another user, export the script to a file and send the file to the other user for import into their script manager.

There may also be scripts available for download at www.macaos.com/support/panelscripts.