Surface mount assembly (SMT) includes a crucial role to learn from the New service Introduction (NPI) process for electronics manufacturing.
The high level of automation from the SMT methodology provides 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 with an electronics manufacturing services (EMS) provider can be separated into four key stages:
Solder Paste Printing
Pick and set
Oven Profiling
Automated Optical Inspection (AOI)
With respect to the complexity in the design, or perhaps your own outsourcing strategy, your product could move through each of these processes consequently, otherwise you might find that you just omit a stride or two.
We would like to highlight the particular attributes, and also the vital importance, of the solder paste printing process for the NPI.
Fitting in with your specifications
The initial step for the EMS provider will be to analyse the printed circuit board (PCB) data which is specific in your order, to make sure that they select the required stencil thickness and the the most suitable material.
Solder paste printing is easily the most common approach to applying solder paste to a PCB. Accurate solder paste application is hugely important in avoiding assembly defects that may use a knock on effect further around the production process. So it is vital that key stage is correctly managed and controlled through your EMS partner.
Solder paste is basically powdered solder which was suspended within a thick medium called flux. The flux behaves as a kind of temporary adhesive, holding the parts in position until the soldering process begins. Solder paste is used on the PCB utilizing a stencil (generally stainless steel, but occasionally nickel,) then when the solder is melted it forms an electrical/mechanical connection.
The thickness in the stencil is what determines the total number of solder applied. For a few projects it could also be required to have a lot of thicknesses in several areas within the one stencil (sometimes called a multi-level stencil).
Another primary factor to take into consideration from the solder printing process is paste release. The proper type of solder paste should be selected in relation to how big is the apertures (or holes) within the stencil. In the event the apertures are very small, as an example, then a solder paste could possibly be quite likely going to sticking with the stencil and not adhering correctly towards the PCB.
Controlling the rate of paste release however can be managed, either by causing changes to the design of the aperture or by reducing the thickness in the stencil.
The sort of solder paste utilized also can effect on the ultimate top printing quality, so it is vital that you find the appropriate mix of solder sphere size and alloy for your project, and also to make sure it is mixed towards the correct consistency before use.
Ensuring quality
After the stencil continues to be designed along with your EMS partner is getting ready to generate the first PCB, they will next want to think about machine settings.
Put simply, the flatter you can keep the PCB over the printing process, the greater final results will be. So by fully supporting the PCB during the printing stage,either through automated tooling pins or with a dedicated support plate, your EMS provider can eliminate the possibility of any defects for example poor paste deposit or smudging.
It’s also important to look at the speed and pressure in the squeegees throughout the printing process. One solution is going to be get one speed for that solder paste but to own varying degrees of pressure, depending on the unique specifications from the PCB as well as the entire squeegee.
Cleansing the stencils, both ahead of and throughout production, is likewise essential in ensuring qc. Many automatic printing machines have a system that can be set to scrub the stencil from a fixed variety of prints which helps to avoid smudging, and prevents any blockages with the apertures.
Finally too, the printers needs to have a built-in inspection system (including Hawk-Eye optical inspection) that may be preset to evaluate the presence of paste throughout the whole PCB after printing.
The solder paste printing process is a precise and detailed one which have a significant part to try out from the ultimate success of the new product. And, since this article highlights, a lot of detailed jobs are more likely to take place c = continual reporting before your EMS partner solders the initial electronic element of a board.