How to choose the suitable thickness of SMT stencils?

What are the thicknesses of SMT stencils? What’s the most suitable thickness for an SMT stencil? Customers asked such similar questions many times.

In fact, the stainless steel SUS304 used in SMT stencils is nothing more than the conventional thickness including: 0.05MM, 0.08MM, 0.1MM, 0.12MM, 0.13MM, 0.15MM, 0.18MM, 0.2MM, 0.25MM, 0.3MM and so on. The above thicknesses are common thickness for laser stencils, of which 0.05mm – 0.15mm is generally the thickness required for the solder paste SMT stencil, and 0.18mm – 0.3mm is generally the thickness required for the red glue stencil.

How to choose the thickness of SMT stencil? For example, if I need an SMT stencil, what is the basis for determining which steel sheet I need to use? To answer this question, we need to bring into two major parameters:

• Aspect Ratio

The width of aperture / thickness = W/T

The lowest acceptable aspect ratio is 1.5.

• Area Ratio

Surface area of aperture / surface area of the aperture walls = L x W/ (2 x (L+W) x T)

The lowest acceptable area ratio is 0.66. Above two factors are the key points for stencil thickness, we usually determine the required thickness of the stencil according to the information provided by the customer or the BGA on the PCB board or the minimum PITCH and minimum CHIP components of the IC. As per below standard:

Components type	Pitch (mm)	Stencil thickness (mm)
Chip	0201	0.12
	0402	0.10
QFP & QFN	0.65	0.15
	0.50	0.13
	0.40	0.12
	0.30	0.10
BGA	1.25+	0.15
	1.00	0.13
	0.5-0.8	0.12

However, this table is normally suited to solder paste stencil; for red glue stencil, the thickness is 0.18mm normally, please be aware of this.

If the customer required special steel thickness, this will be a priority consideration when make.

What’s the normal thickness of SMT stencils?

The conventional paste stencil thickness including: 0.04mm, 0.05mm, 0.08mm, 0.1mm, 0.12mm, 0.13mm, 0.15mm, 0.18mm, 0.2mm, 0.25mm, 0.3mm and so on.

What is the difference between SMT and SMD?

SMD, short for surface mounted device, is an electronic component that you would find on a board.
SMT, short for surface mount technology, is the method of placing components (like an SMD) on the board.

How many IC package types are there?

The common IC package type including BGA(Ball Grid Array)，QFP(Quad Flat Package), SOP(Small out-Line Package), LCC(Leaded Chip Carrier), QFN(Quad Flat No-lead Package), DIP(Double In-line Package) etc.

How many kinds of paste stencils are there？

1) Mylar and Kapton SMT Stencils, used mainly by students and hobbyists to assemble prototype printed circuit boards;
2) Laser cut SMT stencil, most common paste stencil type nowdays;
3) Electroformed stencil, offer the best paste release characteristics and frequently used for fine pitch SMT applications such as BGA;
4) Step stencil, with two or more different stencil thickness in a same steel plate, because different components have paste requirement;
5) Nano Coated Stencils, very high precision of the opening position ,Smart SMT Tools has leveraged its chemistry knowledge to develop unique nano coatings that improve various steps in the PCB Assembly process.

Need to order a SMT Stencils right now? Go to Smart SMT Tools.