Stencil Area Ratio & Paste Volume
From pad size and stencil thickness, compute area ratio, aspect ratio and paste volume to predict insufficient paste on fine-pitch pads — a DFM self-check.
Key points
Stencil Area Ratio & Paste Volume: From pad size and stencil thickness, compute area ratio, aspect ratio and paste volume to predict insufficient paste on fine-pitch pads — a DFM self-check. Formula: Area ratio = W·L / [2T(W+L)] ≥ 0.66 ｜ aspect ratio = W/T ≥ 1.5. Enter parameters on the DD-CAT IDE online tool page to get results instantly, with a calculation-model diagram that updates with the inputs. Area ratio is aperture area over wall area and reflects transfer efficiency better than the aspect ratio. For 0.5mm-pitch BGA/QFN, use a 0.1mm stencil with nano-coating and 1:1 or slightly reduced (0.95) apertures.
Inputs
Area ratio = W·L / [2T(W+L)] ≥ 0.66 ｜ aspect ratio = W/T ≥ 1.5Calculation model (updates with parameters)
| Area ratio | 0.794 | IPC-7525 recommends ≥ 0.66 |
| Aspect ratio W/T | 2.08 | Recommended ≥ 1.5 |
| Verdict | Pass (standard process) | |
| Pad area | 0.2000 mm² | |
| Theoretical paste volume | 24000000 nL | 0.024000 mm³ |
| Empirical transfer efficiency | 83 % | Rough estimate; opening shape and coating matter |
| Recommended stencil thickness ceiling | 0.150 mm | Derived from an aspect ratio of 1.5 |
Engineering notes
- Area ratio is aperture area over wall area and reflects transfer efficiency better than the aspect ratio.
- For 0.5mm-pitch BGA/QFN, use a 0.1mm stencil with nano-coating and 1:1 or slightly reduced (0.95) apertures.
FAQ
- What is Stencil Area Ratio & Paste Volume for?
- From pad size and stencil thickness, compute area ratio, aspect ratio and paste volume to predict insufficient paste on fine-pitch pads — a DFM self-check.
- What is the formula for Stencil Area Ratio & Paste Volume?
- Core formula: Area ratio = W·L / [2T(W+L)] ≥ 0.66 ｜ aspect ratio = W/T ≥ 1.5. The tool returns results instantly using this formula and the selected parameters.
- What engineering notes should I keep in mind when using Stencil Area Ratio & Paste Volume?
- Area ratio is aperture area over wall area and reflects transfer efficiency better than the aspect ratio. For 0.5mm-pitch BGA/QFN, use a 0.1mm stencil with nano-coating and 1:1 or slightly reduced (0.95) apertures.