PCBA SMT service including:
•Lead-free/SMIC solder paste
•Lead-free/SMIC solder paste
•AOI&X-ray test for BGA
•Fine pitch 0.1mm
•Laser cut stencil/step stencil
Two options for turn-key prototyping & PCBA SMT
Semi-automatic assembly: Considering the cost, our engineer will recommend semi-automated assembly for prototype PCB project, if based on dozens of pieces, it is recommended automatic soldering.
What is the semi-automatic placement?
Half work finished manually, half work completed by machine.
How to ensure proper soldering?
We have developed specific software to proofread the assembly drawing, this can avoid any stupid mistake if engineers operate with this software step by step. There will no error on component placement and directional error (like diodes, ICs, etc).
There is the first article inspection based on the specific BOM from customer (means our engineer will cross check the quantity, dimension, width, length of each component. Also proofreading the resistors value, capacitors value, if the IC footprint and component model are the same as the BOM specified or not.) This also involves proofreading component coordinates, and then p/p & programming.
There are Four basic/important points must be followed to promise final assembly quality:
First – Stencil quality
According to the components footprint from PCB board to decide which kind of stencil should be used. If there are the BGA components/gold finger pads/serried multi-pin on the PCB board, we must use such kind of stencil: laser electrolytic polished stencil which can promise the via wall no burr or be glossy during stencil making, also can promise the quality stencil printing (same principle to be used for deciding the stencil thickness).
Second: Solder paste
Before stencil printing, we have to make sure that the stencil surface and via wall are glossy. (Manual and automatic stencil printing is different. Biggest difference in automatic printing is well defined dynamics than manual handling. Although this is a simple operating, but if poor stencil printing, will cause big problem in reflow soldering.
Paste tin is very important as well, but some suppliers will choose very common tin paste with low silver content and procured by low quality raw material to save cost, regardless of quality, this will lead to cracks rough PCBA soldering, non-smooth, void soldering, solder paste is insufficient integration, short circuit which caused by tin connection.
So we have to ensure the assembly quality, normally we use two international brands Paste: Japan (SMIC) and the US (ALPHA). Our engineers will select the right solder paste based on different PCB application. The two important parameters for paste selection is are the magnitude and silver melting temperature.
Third: Preparation work before reflow
24 hours before soldering, all the IC, BGA type integrated circuit components should be bake in the oven to be dehumidified. The big characteristics of IC, BGA are highly integrated, complex internal structure. It will be from a variety of materials, there are a lot of internal gaps. Due to characteristics of an integrated circuit, when these components are placed at ordinary temperature and humidity conditions, the gap will absorb the moisture in the air. The damp IC, BGA and other components will be expanded once they are in high temperature, especially during reflow process, and they can’t be restituted. It will cause internal component stress disorder, which causes cracking, delaminating, peeling, micro-cracks and other phenomena. And adverse, there will be a direct result of severe popcorn, seriously affecting the quality of the components. Hence, the Component bake work is very necessary to remove such moisture before reflow soldering.
Before reflow, our engineer will decide the speed of reflow according to design request, components footprint, quantity and the thickness of the PCB board.
Must be AOI & X-Ray inspection for BGA
For high-quality assurance it is required to optimize process in details.
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