Chapter 5: How to Build a BGA Part

BGA (Ball Grid Array) IC packages are often a critical component in a circuit, one of the more expensive parts in a BOM, and one of the package styles most sensitive to thermal and mechanical loads. Common types are standard overmolded BGAs, flip chip BGAs (lidded, unlidded, or with stiffener rings), or ceramic BGAs. Because these parts are so important, Ansys recommends characterizing a sample part to determine CTE to correlate predictions with qualification data if available.

ID Tab

Part Type: Typically, IC. Less commonly: VOLTAGE REGULATOR or TRANSDUCER—which are made with this form factor. Refer to the part data sheet.
Failure Class: This can be left blank. The property is not used in any Sherlock stand-alone analysis. It is only used when Sherlock is part of a multi-tool analysis workflow.

BGA Part Properties:

5.1. BGA Package Properties

Package Tab

Package Name: Example: BGA-24. Refer to the part data sheet. Supported values are defined in the package data files provided by Sherlock or user-defined package data files. See Package Management in the Sherlock User's Guide.
Tip: You can enter the Package Name manually, or you can use Sherlock's Package Chooser which helps you select a prebuilt part that approximates the one you are building. Sherlock then auto-populates all the relevant properties. These package properties are based on industry standards, so you may have to edit the properties to match the part you are building. To open the Chooser, click the … icon (A, below). See The Package Chooser in the Sherlock User's Guide for more information.
Package Type: BGA
Package Mount: SMT
Package Length: Refer to the part data sheet drawing.
Package Width: Refer to the part data sheet drawing.
Overmold Thickness: Refer to the part data sheet drawing.
Tip: If the data sheet does not specify Laminate and Overmold Thickness separately, you can assume about two thirds of the overall package thickness is the overmold and one third is the laminate.
Laminate Thickness: From datasheet drawing
Tip: See tip above under Overmold Thickness.
Model Part: ENABLED
Corner Shape: Typically, SQUARE.
A = Square Corner • B = Miter Corner • C = Round Corner • Arrows show corner radius.
Corner Radius: For SQUARE, the radius is 0. See image above for MITER and ROUND corners.
Corner Face: TOP_BOTTOM. See image below.
D = TOP_BOTTOM • E = FRONT_BACK • F = LEFT_RIGHT
Substrate Material: Usually LAMINATE-BGA, but see notes below.
- The LAMINATE-BGA material from the Sherlock library represents a generic assumption for mechanical properties that Ansys has found match average effective properties for a range of BGA packages. However, if component CTE data is available, a custom laminate material should be entered. See Laminate Management in the Sherlock User's Guide.
- CBGAs, or ceramic BGAs, require a ceramic substrate. ALUMINA is often used.
Overmold Material: OVERMOLD-BGA
- For unlidded flip-chip BGAs, no overmold material is necessary
- For lidded components or those with stiffener rings, COPPER is the typical material. The overmold thickness in those cases should be adjusted so the prediction matches qualification test data which requires a thickness of around 0.4 or 0.6 mm.

5.2. BGA Ball Properties

Ball Tab

Ball Pattern: Refer to part data sheet drawing.
Ball Count: Refer to part data sheet drawing.
Ball Pitch: Refer to part data sheet drawing.
Ball Pitch: Distance between adjacent solder balls for a BGA component
Ball Diameter: Refer to part data sheet drawing.
Tip: The image below illustrates Ball Diameter, Ball Package Diameter, Ball Diameter, Ball Pad Diameter, and Ball Height. For a detailed discussion on these properties, see Solder Ball Modeling in the Sherlock User's Guide.
Ball Package Diameter: Refer to part data sheet drawing.
Ball Pad Diameter: Refer to part data sheet drawing.
Tip: Often, data sheets do not provide Ball Package Diameter or Pad Diameter. As an approximation, use 90% of the Ball Diameter.
Ball Height: Refer to part data sheet drawing.
Tip:
- For Ball Height, use max dimension, not nominal.
- Datasheet dimensions for solder balls show the geometry of the loose component before reflow with solder paste. Add 70 to 100 μm to the stated ball height. For larger BGAs (40 x 40 mm), the high mass of the component will cause the solder balls to collapse slightly, so this edit is not needed.
For Ball Grid Layout Properties (Ball Chan Width, Ball Modeling, Ball Perimeter Rows, Ball Perimeter Cols, Ball Island Rows, Ball Island Cols), refer to the datasheet drawing, and see notes below.
Tip: The solder ball modeling properties mentioned in this section are discussed in detail in Solder Ball Modeling in the Sherlock User's Guide.
- Ball layouts often come in standard patterns that are defined in Sherlock: FULL (A, below), PERIMETER (B), CHANNEL (C), or ISLAND (D).
- For non-standard layouts, the NETLIST Ball Pattern option will extract ball location information from the PCB design files. NETLIST will also correctly populate ball locations for standard grid layouts.
- To correctly populate Ball Chan Width, Rows, and Columns for standard BGA layouts, remember:
  - Ball Channel Width applies only to Perimeter (A in the image below), Channel (B), and Island (C) patterns.
  - To Calculate Ball Channel Width
    Ball Channel Width = [ball pitch] x [the number of ball columns on one side of the gap]
  g = gap • gold rectangle = ball columns (three columns in each example) • p = ball pitch
  Tip: In some cases, setting the correct ball pattern properties can be confusing. To confirm your work is correct, view the component in Sherlock's 3D Viewer to verify the accuracy of the model. See Checking Your Work.
Ball Material: Refer to the part data sheet. Ball Material is the type of solder ball used to connect the BGA to the PCB. Supported values are defined in the solder data file provided by Sherlock and/or a user-defined data file.
Tip: BGA components may be assembled with solder balls composed of a different alloy than what was selected for the PCB solder paste.
Ball Modeling: NONE, ONE ELEMENT, TWO ELEMENT, or ADVANCED. For a detailed discussion on ball modeling types, see Solder Ball Modeling in the Sherlock User's Guide.

5.3. BGA Solder Properties

Solder Tab

Solder Material: Typically, DEFAULT
When set to DEFAULT, Sherlock uses the Default Solder Type specified in the Circuit Card Properties. To view or edit these properties, right-click the circuit card in the Project Tree and select Circuit Card Properties in the context menu.
If a solder other than the default is used for this part, you may enter the name of the solder in the Solder Material field. To add a custom solder to the Solder Library, see Solder Management in the Sherlock User's Guide.
Solder Thickness: Sherlock calculates this value. It is based on the stencil thickness as recorded in the Circuit Card Properties and is assumed to be half that value.
To view or edit Circuit Card Properties, right-click the circuit card in the Project Tree and select Circuit Card Properties in the context menu.
Solder Model: BGA Model. This solder model is valid for all BGAs.

5.4. BGA Die Properties

Tip: In addition to the information below, refer to the Die Properties Guide.

Die Tab

Tip: Manufacturers rarely provide die dimensions. When this is the case, Ansys recommends assuming half the package outline.

Die Length: Assume half Package Length.
Die Width: Assume half Package Width.
Die Thickness: If not provided by the manufacturer, assume the following:
- For a package thickness of 1.0 mm and below, Die Thickness is between 0.185 and 0.2 mm.
- For packages thicker than 1.0 mm, assume a Die Thickness of 0.4 mm.
- For memory devices, Die Thickness is generally between 0.2 and 0.25 mm.
Die Material: This is the primary material of the die. Material names are defined in the material data file provided by Sherlock and/or a user-defined data file.
Process Node: This field is for informational purposes only. The property is not used in any of Sherlock's standard analyses.