Surface mount assembly (SMT) has a crucial role to learn in the New service Introduction (NPI) process for electronics manufacturing.
The prime level of automation from the SMT methodology comes with a various 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 can be broken down into four key stages:
Solder Paste Printing
Pick and Place
Oven Profiling
Automated Optical Inspection (AOI)
Based on the complexity with the design, maybe own outsourcing strategy, your products could pass through all these processes therefore, or else you might find that you just omit a step or two.
We should highlight the specific attributes, as well as the vital importance, in the solder paste printing process on your NPI.
Fitting in with your specifications
The first step on your EMS provider may be to analyse the pcb (PCB) data which is specific in your order, to make sure that they choose the required stencil thickness and also the the most suitable material.
Solder paste printing is the most common technique of applying solder paste with a PCB. Accurate solder paste application is hugely essential in avoiding assembly defects which may possess a knock on effect further down the production process. So it’s vital that this key stage is correctly managed and controlled from your EMS partner.
Solder paste is basically powdered solder that is suspended within a thick medium called flux. The flux behaves as a form of temporary adhesive, holding the parts set up before the soldering process begins. Solder paste is applied to the PCB using a stencil (generally stainless, but occasionally nickel,) then after the solder is melted it forms an electrical/mechanical connection.
The thickness from the stencil is exactly what determines the level of solder applied. For a few projects it might be also important to have a lot of thicknesses in numerous areas within the one stencil (often referred to as a multi-level stencil).
Another important element to take into consideration from the solder printing process is paste release. The right kind of solder paste should be selected in relation to the size of the apertures (or holes) inside stencil. When the apertures have become small, for instance, then the solder paste may be prone to sticking to the stencil rather than adhering correctly on the PCB.
Managing the rate of paste release however can be simply managed, either by making changes for the kind of the aperture or by reducing the thickness with the stencil.
The type of solder paste which is used also can affect a final top printing quality, therefore it is vital that you choose the appropriate mix of solder sphere size and alloy for your project, and help it become mixed to the correct consistency before use.
Ensuring quality
As soon as the stencil continues to be designed and your EMS partner is able to make the first PCB, they’ll next want to think about machine settings.
Put simply, the flatter you can the PCB with the printing process, the higher the final results will probably be. So by fully supporting the PCB throughout the printing stage,either by the use of automated tooling pins or having a dedicated support plate, your EMS provider can take away the possibility of any defects such as poor paste deposit or smudging.
It’s also important to think about the speed and pressure in the squeegees in the printing process. One solution is going to be have one speed to the solder paste but to own varying degrees of pressure, depending on the unique specifications of the PCB as well as the entire squeegee.
Cleaning the stencils, both ahead of and throughout production, is likewise essential in ensuring quality control. Many automatic printing machines have a system which can be set to completely clean the stencil after a fixed amount of prints which will help to stop smudging, and prevents any blockages in the apertures.
Finally too, the printers should have a built-in inspection system (for example Hawk-Eye optical inspection) which can be preset to evaluate the use of paste over the whole PCB after printing.
The solder paste printing process is really a precise and detailed the one which have a significant part to try out in the ultimate success of one’s new product. And, because this short article highlights, so much detailed work is more likely to occur under the surface before your EMS partner solders the first electronic component to a board.
