Surface mount assembly (SMT) carries a crucial role to experience inside the New service Introduction (NPI) process for electronics manufacturing.
The prime degree of automation inside 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 put
Automated Optical Inspection (AOI)
Based on the complexity in the design, or perhaps your own outsourcing strategy, your products or services could move across all these processes subsequently, otherwise you may find that you simply omit one step or two.
We want to highlight the specific attributes, along with the vital importance, in the solder paste printing process for your NPI.
Fitting in with your specifications
The initial step to your EMS provider may be to analyse the printed circuit board (PCB) data that is certainly specific for your order, to ensure they select the required stencil thickness and also the the best option material.
Solder paste printing is easily the most common technique of applying solder paste to some PCB. Accurate solder paste application is hugely critical in avoiding assembly defects which could use a knock on effect further along the production process. So it will be vital this key stage is correctly managed and controlled by your EMS partner.
Solder paste is actually powdered solder that is suspended within a thick medium called flux. The flux behaves as a form of temporary adhesive, holding the components available prior to the soldering process begins. Solder paste is used for the PCB by using a stencil (generally metal, but occasionally nickel,) then after the solder is melted it forms an electrical/mechanical connection.
The thickness of the stencil is the thing that determines the volume of solder applied. For some projects it might also be required to have a lot of thicknesses in different areas within the one stencil (known as a multi-level stencil).
Another primary factor to take into consideration in the solder printing process is paste release. The best sort of solder paste should be selected based on the dimensions of the apertures (or holes) within the stencil. When the apertures are very small, as an example, then a solder paste might be more prone to sticking to the stencil rather than adhering correctly on the PCB.
Manipulating the rate of paste release however can be easily managed, either start by making changes for the kind of the aperture or by reducing the thickness from the stencil.
The type of solder paste that is used can also effect on the final top printing quality, so it’s important to find the appropriate combination of solder sphere size and alloy for your project, and also to help it become mixed for the correct consistency before use.
When the stencil has become designed plus your EMS partner is getting ready to produce the first PCB, they’re going to next be considering machine settings.
To put it differently, the flatter you can maintain the PCB through the printing process, the greater the final results will probably be. So by fully supporting the PCB throughout the printing stage,either by way of automated tooling pins or using a dedicated support plate, your EMS provider can get rid of the chance for any defects like poor paste deposit or smudging.
You’ll want to think about the speed and pressure in the squeegees throughout the printing process. One solution is to get one speed for the solder paste but to get varying degrees of pressure, in line with the unique specifications from the PCB and also the length of the squeegee.
Cleaning the stencils, both ahead of and throughout production, is likewise essential in ensuring qc. Many automatic printing machines possess a system that could be set to completely clean the stencil after a fixed amount of prints which assists to stop smudging, and prevents any blockages with the apertures.
Finally too, the printers really should have a built-in inspection system (such as Hawk-Eye optical inspection) that may be preset to monitor a good paste across the whole PCB after printing.
The solder paste printing process can be a precise and detailed the one that have a significant part to play within the ultimate success of one’s new product. And, simply because this article highlights, so much detailed tasks are prone to take place behind the curtain before your EMS partner solders the initial electronic element of a board.