Surface mount assembly (SMT) includes a crucial role to play from the New Product Introduction (NPI) process for electronics manufacturing.

Our prime level of automation from the SMT methodology offers a number of advantages, from automatic correction of errors, to simpler and faster assembly, better mechanical performance, increased production rates and reduced labour costs.

The SMT assembly process to have an electronics manufacturing services (EMS) provider could be separated into four key stages:

Solder Paste Printing
Pick and put
Oven Profiling
Automated Optical Inspection (AOI)
Depending on the complexity in the design, or your own outsourcing strategy, your product could go through these processes in turn, or else you might discover that you just omit a step or two.

We want to highlight the particular attributes, along with the vital importance, of the solder paste printing process on your NPI.

Attempting to your specifications
The first task to your EMS provider may be to analyse the pcb (PCB) data that is specific in your order, to ensure that they pick the required stencil thickness and the the most suitable material.

Solder paste printing is regarded as the common way of applying solder paste into a PCB. Accurate solder paste application is hugely critical in avoiding assembly defects which may have a knock on effect further along the production process. So it will be vital this key stage is correctly managed and controlled through your EMS partner.

Solder paste is essentially powdered solder which has been suspended inside a thick medium called flux. The flux acts as a sort of temporary adhesive, holding the components available prior to the soldering process begins. Solder paste is used on the PCB using a stencil (generally metal, but occasionally nickel,) then as soon as the solder is melted it forms an electrical/mechanical connection.

The thickness of the stencil is the thing that determines the total number of solder applied. For a lot of projects it may well be required to have several thicknesses in various areas within the one stencil (known as a multi-level stencil).

Another key factor to consider inside the solder printing process is paste release. The proper kind of solder paste must be selected based on the size of the apertures (or holes) inside stencil. If the apertures are incredibly small, for example, then the solder paste could possibly be very likely to adhering to the stencil and never adhering correctly towards the PCB.

Governing the rate of paste release however can easily be managed, either by looking into making changes to the design of the aperture or by reducing the thickness from the stencil.

The sort of solder paste that is used also can effect on the last top printing quality, so it is imperative that you find the appropriate blend of solder sphere size and alloy for that project, and also to ensure it is mixed for the correct consistency before use.

Ensuring quality
After the stencil has become designed as well as your EMS partner is preparing to make the first PCB, they’re going to next want to think about machine settings.

Quite simply, the flatter you can the PCB with the printing process, the greater the end result will be. So by fully supporting the PCB in the printing stage,either by the use of automated tooling pins or with a dedicated support plate, your EMS provider can get rid of the possibility of any defects such as poor paste deposit or smudging.

It’s also important to think about the speed and pressure of the squeegees through the printing process. One solution is usually to have one speed for your solder paste but to possess varying degrees of pressure, based on the unique specifications with the PCB as well as the length of the squeegee.

Cleaning the stencils, both just before and throughout production, may also be essential in ensuring qc. Many automatic printing machines have a system that may be set to completely clean the stencil after a fixed number of prints which will help to avoid smudging, and prevents any blockages with the apertures.

Finally too, the printers needs to have a built-in inspection system (for example Hawk-Eye optical inspection) which may be preset to monitor the existence of paste across the whole PCB after printing.

The solder paste printing process can be a precise and detailed the one that may significant part to play in the ultimate success of the cool product. And, because this blog post highlights, a lot of detailed jobs are planning to occur behind the curtain before your EMS partner solders the 1st electronic ingredient of a board.