Opening process standard of Stencil

As default, JLCPCB engineer will optimize the production file for the apertures according to the following standard. By following this standard, the apertures are supposed to be better for solder paste releasing or soldering effect. If you don't require this standard,or want apertures exactly the same as your paste layer, please leave a remark when ordering.

Opening process standard of Solder Paste Stencil

1. IC Category (W represents Width, L represents Length)

(1) PITCH = 0.8 - 1.27 mm: The width is generally set between 45% and 60% of the PITCH, with the specific value depending on the pad size on the circuit layer. For smaller pads on the circuit layer, choose a smaller width, and for larger pads, choose a larger width.

(2) PITCH = 0.635 - 0.65 mm: W = 0.3 - 0.33 mm, L = 1 mm, with rounded corners on both ends.

(3) PITCH = 0.5 mm: W = 0.24 mm, L: If less than 1.5 mm, extend outward by 0.1 mm, with rounded corners on both ends.

(4) PITCH = 0.4 mm: W = 0.19 mm, L: Extend outward by 0.1 mm, with rounded corners on both ends.

(5) PITCH = 0.35 mm: W = 0.17 mm, L: Extend outward by 0.1 mm, with rounded corners on both ends.

(6) PITCH = 0.3 mm: W = 0.16 mm, L: Extend outward by 0.1 mm, with rounded corners on both ends (if the length is <0.8 mm, extend the length outward by 0.15 mm).

For the above (0.65 - 1.27), if L < 1 mm, the length needs to be extended outward by 0.1 mm.

2. BGA Category

PITCH = 0.4 mm, open 0.23 mm square with rounded corners

PITCH = 0.45 mm, open 0.26 mm

PITCH = 0.5 mm, open 0.3 mm

PITCH = 0.65 mm, open 0.35 mm

PITCH = 0.8 mm, open 0.45 mm

PITCH = 1.0 mm, open 0.55 mm

PITCH = 1.27 mm, open 0.65 mm

Important Notes:

For 0.4 PITCH, open a 0.23 mm square with rounded corners.

3.  Resistor and capacitor pads

For resistor and capacitor pads which are 0805 and larger ones, anti-solder bead treatment will be applied as below.  What's solder bead? https://jlcpcb.com/help/article/Solder-beading-Treatment

4. SOT252, SOT223 and other high-power transistors

The apertures need to bridge in the middle, or divided into a number of small pieces. Bridge width depends on the pad size, as shown in the following figure.

The main purpose is that the biggest problem in the SMT processing and welding of such large-sized heat sinks is the void problem. The voids in the PCBA solder joints are formed because the volatile components in the solder paste flux or the waste gas generated during the cleaning process cannot be completely discharged and are wrapped in the solder joints. Due to the extremely small gap between the bottom of the component and the PCB pad, these gases are not easy to discharge. The presence of voids will seriously reduce the heat dissipation effect and affect the reliability of the product.

5. Through-Hole pads in Stencil

If there are no solder paste layer or the through hole pads are not designed on the solder paste layer, the apertures for through-hole components will not be open in stencil as default. Please design it on the solder paste layer correctly or leave a remark when you ordering.

Opening process standard of Red Glue Stencil

(1) 0402 Components: Width opening 0.26 mm, length extended by 0.15 mm.

0603 Components: Width opening 0.28 mm, length extended by 0.20 mm.

0805 Components: Width opening 0.32 mm, length extended by 0.20 mm.

1206 Components: Width opening 0.5-0.6 mm (or 30%-35% of the pad spacing).

For components above 1206: Width opening 35%, length extended by 0.2 mm.

When the gap between 0603 components is greater than 0.75 mm, width opening 0.32 mm.

When the gap between 0805 components is greater than 0.95 mm, width opening 0.35 mm.

For diodes: Width according to 35%-40% of the inner distance, length extended by 0.25 mm.

For components other than diodes, if it's difficult to determine the type, open about 30% of the inner distance. If the inner distance is too small, adjust according to the situation.

(2) SOT23

L1 = 110% L

W2 = W/2 (centered opening)

W1 = 0.3~0.5 mm

(3) SOT89

W=0.4mm

L1=L

(4)SOT233 & SOT252

W1 = 30% W

If 0.5 ≤ W1 ≤ 2.5 mm (open near the larger pad)

W2 = W/3

L1 = 110% L

If W ≥ 3.5 mm, a bridge is required, with a bridge width of 0.3 mm

2. Resistor and Capacitor Arrays L

D = 45% W

W1 = 1/2 W

L1 = L

When D > 3 mm, set D = 3 mm. The number of middle circular points depends on the size of the IC, with a minimum of 2 and a maximum of 5.

When the opening width is less than 0.35 mm, please make it a 0.35 mm rectangle.

3. IC, QFP

D = 45% W

W1 = 1/2 W

L1 = L

When D > 3 mm, set D = 3 mm. The number of middle circular points depends on the size of the IC, with a minimum of 2 and a maximum of 5.

D = 1.3-3.5 mm (specifically depending on the size of the QFP; if it is too small, the middle opening can be omitted)

Circular hole position: The outer edge of the circular hole should be aligned with the outermost end of the QFP's pins.

The above can be opened as a square hole according to 35-40% of the inner distance. If the width is greater than 1.5 mm, please open it as a circular hole according to the above requirements.