Stencil Manufacturing

Ⅰ: Stencil Manufacturing

1. Chemical Etching

▪ Features: one-time molding, fast speed; The price is cheap.

2. Laser Cutting

▪ Features: High accuracy of data production, smaller effect on objective factors; Trapezoidal opening is good for demoulding. It can achieve precision cutting. The price is moderate.

3. Electrotyping forming

▪ Features: smooth hole wall, especially suitable for super fine spacing stencil production

Ⅱ: The opening design

• The opening design of the stencil should consider the release of the solder paste, which is determined by three factors:

• Of the three factors, the latter two factors are determined by the manufacturing technology of the stencil, but the former one is considered more.

• First of all, we know width-to-thickness ratio and area ratio: width-to-thickness ratio: the ratio of the width of the opening to the thickness of the stencil. Area ratio: the ratio of the opening area to the cross-sectional area of the hole wall.

• Nevertheless,when we design the opening of the stencil, we should not blindly pursue the ratio of width-to-thickness or the ratio of area but ignoring other process problems, such as bridging and excess solder. The minimum safety distance from pads to pads is 0.25mm.

Stencil (SMT template) opening design tips:

1. fine spacing of IC/QFP, in order to prevent stress concentration, it is the best to pour R=0.05mm fillet at both ends; Square hole of BGA, 0402 and 0201 is the same.

2. During the stencil designing, the width of the opening should ensure that at least 4 maximum tin balls can pass through smoothly.

Ⅲ: Post processing

• After laser cutting, metal slag will be attached to the wall and the opening, therefore, it is generally necessary to polish the surface; Nevertheless, polishing is not only to remove the slag (burr), it is also need surface Roughing Treatment of the sheet steel to increase the surface friction, rectin paste rolling and achieve a good tin effect. electropolishing" can also be chosen to improve the hole wall for complete slag removal (burr) as necessory.

• According to different production process, the raw materials and opening design will have an important impact on the quality of stencil, thus, it is necessary to master the production process and specification of stencil.