Surface mount assembly (SMT) features a crucial role to experience from the New service Introduction (NPI) process for electronics manufacturing.
Our prime amount of automation within the SMT methodology provides 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 for an electronics manufacturing services (EMS) provider could be categorised into four key stages:
Solder Paste Printing
Pick and set
Automated Optical Inspection (AOI)
Depending on the complexity with the design, maybe own outsourcing strategy, your product could move across these processes consequently, otherwise you may find that you just omit one step or two.
We should highlight the particular attributes, as well as the vital importance, with the solder paste printing process on your NPI.
Working to your specifications
The initial step for your EMS provider can be to analyse the pcb (PCB) data that is specific on your order, to ensure that they choose the required stencil thickness and also the the most suitable material.
Solder paste printing is the most common way of applying solder paste with a PCB. Accurate solder paste application is hugely essential in avoiding assembly defects which can have a very knock on effect further around the production process. So it’s vital this key stage is correctly managed and controlled from your EMS partner.
Solder paste is basically powdered solder which has been suspended inside a thick medium called flux. The flux acts as a kind of temporary adhesive, holding the constituents available until the soldering process begins. Solder paste is applied to the PCB employing 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 level of solder applied. For many projects it might be also necessary to have several thicknesses in various areas inside one stencil (often referred to as a multi-level stencil).
Another key factor to consider in the solder printing process is paste release. The right kind of solder paste should be selected in relation to how big is the apertures (or holes) from the stencil. When the apertures are extremely small, for example, then this solder paste could be quite likely going to sticking to the stencil rather than adhering correctly for the PCB.
Manipulating the rate of paste release however can easily be managed, either by making changes on the design of the aperture or by reduction of the thickness in the stencil.
The type of solder paste that is used also can effect on the final print quality, therefore it is vital that you select the appropriate mix of solder sphere size and alloy for the project, and also to makes it mixed towards the correct consistency before use.
After the stencil continues to be designed and your EMS partner is ready to generate the first PCB, they’ll next want to consider machine settings.
Quite simply, the flatter you can maintain the PCB with the printing process, the better the end result will be. So by fully supporting the PCB through the printing stage,either through automated tooling pins or having a dedicated support plate, your EMS provider can eliminate the potential for any defects such as poor paste deposit or smudging.
It’s also important to look at the speed and pressure in the squeegees through the printing process. One solution is going to be have one speed for that solder paste but to get varying examples of pressure, using the unique specifications from the PCB and the length of the squeegee.
Cleaning the stencils, both just before and throughout production, may also be crucial in ensuring qc. Many automatic printing machines possess a system that can be set to completely clean the stencil after having a fixed number of prints that helps to prevent smudging, and prevents any blockages in the apertures.
Finally too, the printers really should have a built-in inspection system (like Hawk-Eye optical inspection) that may be preset to evaluate a good paste throughout the whole PCB after printing.
The solder paste printing process is often a precise and detailed the one which will have a significant part to try out from the ultimate success of the new product. And, since this article highlights, plenty of detailed jobs are more likely to occur c = continual reporting before your EMS partner solders the very first electronic aspect of a board.