Learn to BGA rework station process of repair
The current international research has enhanced the trend of integrated circuit development to the area array package. BGA (ball grid array), CSP (chip-scale package) and flip chip (flip chip) not only in the printed circuit board unit area to provide much larger input / output (I / O), but also provide obvious Electrical, mechanical and unit cost advantages. Increased assembly density, reduced feature size and package reduces the distance between electrical signals, resulting in improved speed and performance. So the number of flip chips and other advanced packages is expected to increase dramatically in 2002, reaching nearly $ 2 billion in 2003.
The progress of the assembly equipment has been prepared for an acceptable ppm loss rate in the production process. However, for many companies, high-quality repair is still a costly nightmare. A more thorough understanding of the area arrangement package and its production parameters can reduce the fear of BGA repair, ensure process control, and save significant rework costs.
Based on the historical experience of most operators, three repair problems are still extremely important:
In the process, the components are removed from the board without damaging the substrate, pads and adjacent elements
Reattach the components in a process controlled manner
Check the quality of the process
Those that promote fine pitch, external pin components such as QFP (quad flat pack) develop density and performance requirements, from handling point of view, manual welding and inspection, resulting in adequate repair of headache. Although the area arrangement package does not have the same handling problem, the welding process can not be done with a typical repair tool, and it is very difficult to check. If the estimates of the expected amount of these components are correct, then the repair of the area arrangement package must become a viable, user-friendly and cost-effective option for millions of repair operators around the world.
There are several key considerations in the reflow process. On the entire surface of the package and the entire surface of the PCB, the uniform heat distribution and heat transfer are critical. The heating process and the temperature setting must be such that the package reaches the reflux and then melts itself with the solder balls, evenly drops itself onto the pads, forming intermetallic compounds with the pads.
Notice how the components fall, parallel to the PCB, and how all the solder balls are uniform in shape, and are completely "wet" or welded to the pads.
On the contrary, uneven heating will cause the package to fall or tilt unequally to the side or angle that has already reached the return. If the process stops at this time, then the component will not even land itself, will not reach the coplanarity, and therefore will be insufficiently welded.
In addition, for a very small, very light CSP / flip chip component, a key consideration is the flow velocity in the convection oven. Although the lowest airflow velocity is required to conduct heat to the components and PCBs, the speed must not allow these light elements to be blown or moved in the reflow process. When a very small eutectic solder ball is in a liquid state, any movement may cause the solder ball to collapse, causing the element to fall entirely on the plate during reflow.