Paste Volume Calculator
Stencil / Paste Process

Solder Paste Volume Calculator

Calculate aperture volume, paste deposit volume after transfer efficiency, and estimated solder volume after reflow. Includes IPC-7525A area ratio verdict and lead-free aperture reduction guidance.

01 -- The Calculation Chain
Step 1: Aperture Volume
Rectangular: V_ap = L x W x T Circular: V_ap = pi x (D/2)^2 x T
The theoretical volume of paste the aperture can hold if filled 100%. L, W, and D are the actual aperture dimensions. T is stencil foil thickness.
Step 2: Paste Deposit Volume
V_deposit = V_ap x (TE / 100)
Transfer efficiency (TE) is the ratio of actual deposited volume to aperture volume. A well-designed aperture with area ratio above 0.66 typically achieves 85-100% TE. Below 0.66 it becomes erratic.
Step 3: Solder Volume After Reflow
V_solder = V_deposit x MCV
Flux vehicle evaporates during reflow. What remains is the metal. Metal content by volume (MCV) is typically 45-55% for standard pastes. This is the actual solder volume forming the joint.
Area Ratio (IPC-7525A)
AR = (L x W) / (2 x (L+W) x T) Circular: AR = D / (4 x T)
Compares aperture opening area to sidewall area. Above 0.66, paste releases to the pad. Below 0.66, it tends to stick to the walls. IPC-7525A minimum is 0.66 for both laser and electroform stencils.
<0.50 Unreliable 0.50-0.65 Marginal ≥0.66 Reliable
02 -- How To Use It
1

Enter stencil thickness

Use the actual foil thickness ordered from your stencil supplier. Standard values: 0.10, 0.12, 0.15, 0.20 mm. For mixed assemblies with fine-pitch components, this is typically 0.10 or 0.12 mm.

2

Enter pad dimensions and set the scale factor

Enter the PCB land pad dimensions from your layout. The aperture scale factor then converts them to the actual aperture cut in the stencil. 100% means a 1:1 aperture-to-pad ratio, which is the IPC-7525A recommendation for most lead-free components. Fine-pitch ICs typically use 80-90%. BGAs usually stay at 100%. The calculator shows the resulting aperture size before you commit.

3

Set transfer efficiency

If you have SPI data, use your measured average TE. Without SPI data, use 90% as a starting estimate for a well-tuned process with area ratio above 0.66. Drop this toward 70-75% if you have marginal area ratios or known print issues.

4

Select metal content by volume

Check your paste datasheet. Most standard lead-free pastes are 88-92% metal by weight, which corresponds to roughly 47-52% by volume depending on alloy density. If you are unsure, use the 50% default.

03 -- Limitations
This calculator gives geometric estimates. Real deposited volume is influenced by paste rheology, squeegee parameters, stencil coating, board surface finish, print speed, and separation speed. None of those are modeled here. The solder volume after reflow figure does not account for copper dissolution from the pad, intermetallic compound formation, or wetting angle effects on fillet shape. Use these numbers as a process design starting point and a sanity check, not as a substitute for SPI measurement and actual joint cross-section analysis.
Stencil
mm
Typical range: 0.10-0.20 mm. Verify against your stencil order confirmation.
Aperture Shape & Dimensions
mm
mm
mm
0%
%
Enter the PCB pad dimensions above. The scale factor converts them to the actual aperture cut in the stencil. 100% = 1:1 (recommended for lead-free per IPC-7525A). Fine-pitch components typically use 80-90%. BGAs usually stay at 100%.
Transfer Efficiency
90%
Typical range: 85-100% for AR ≥ 0.66. Below 0.66 AR, TE drops toward 60-80% and becomes inconsistent. IPC allows 50-150% (40-140% for fine features). Use your SPI average if available.
Paste Properties
Most standard SAC305 pastes are 88-92% metal by weight, approximately 47-52% by volume. Check your paste datasheet. IPC-HDBK-001H states 24-45% by volume for the general range; higher-load modern pastes commonly reach 50-55%.
pads
Enter to get totals per component. Leave blank for single-pad results only.
Results
Enter stencil thickness and aperture dimensions above to calculate.