Surface mount assembly (SMT) features a crucial role to learn from the New service Introduction (NPI) process for electronics manufacturing.
Our prime amount of automation within the SMT methodology supplies a selection 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 might be separated into four key stages:
Solder Paste Printing
Pick and set
Automated Optical Inspection (AOI)
Based on the complexity of the design, or your own outsourcing strategy, your product or service could go through these processes in turn, otherwise you may find that you omit a measure or two.
We want to highlight the particular attributes, as well as the vital importance, from the solder paste printing process for the NPI.
Working to your specifications
The initial step to your EMS provider will be to analyse the printed circuit board (PCB) data that’s specific in your order, in order that they choose the required stencil thickness and the the best option material.
Solder paste printing is easily the most common way of applying solder paste into a PCB. Accurate solder paste application is hugely important in avoiding assembly defects that may have a very knock on effect further along the production process. So it will be vital that key stage is correctly managed and controlled because of your EMS partner.
Solder paste is essentially powdered solder that has been suspended inside a thick medium called flux. The flux provides for a form of temporary adhesive, holding the parts in position before soldering process begins. Solder paste is applied on the PCB utilizing a stencil (generally stainless steel, but occasionally nickel,) then once the solder is melted it forms an electrical/mechanical connection.
The thickness with the stencil is the thing that determines the volume of solder applied. For many projects it may well also be necessary to have several thicknesses in numerous areas inside one stencil (sometimes called a multi-level stencil).
Another key factor to take into account within the solder printing process is paste release. The right sort of solder paste should be selected dependant on how big the apertures (or holes) inside stencil. In the event the apertures are very small, for example, then the solder paste may be quite likely going to sticking with the stencil rather than adhering correctly to the PCB.
Controlling the rate of paste release however can be managed, either by making changes to the design of the aperture or by lessening the thickness in the stencil.
The type of solder paste which is used may also effect on the last top printing quality, so it is crucial that you select the appropriate mixture of solder sphere size and alloy for your project, and to make sure it is mixed towards the correct consistency before use.
As soon as the stencil has become designed along with your EMS partner is getting ready to produce the first PCB, they will 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 be. So by fully supporting the PCB in the printing stage,either by the use of automated tooling pins or having a dedicated support plate, your EMS provider can remove the potential for any defects including poor paste deposit or smudging.
It’s also important to consider the speed and pressure with the squeegees in the printing process. One solution is usually to get one speed for the solder paste but to get varying numbers of pressure, depending on the unique specifications with the PCB as well as the length of the squeegee.
Cleansing the stencils, both prior to and throughout production, is likewise essential in ensuring qc. Many automatic printing machines possess a system that can be set to scrub the stencil from a fixed number of prints that helps in order to avoid smudging, and prevents any blockages from the apertures.
Finally too, the printers must have a built-in inspection system (including Hawk-Eye optical inspection) that may be preset to monitor the presence of paste across the whole PCB after printing.
The solder paste printing process can be a precise and detailed one which may significant part to try out in the ultimate success of the new product. And, as this blog post highlights, plenty of detailed work is likely to take place c = continual reporting before your EMS partner solders the initial electronic component to a board.