In IPC-SM-782 thereare two important concepts: Producibility Levels and Component MountingComplexity Levels. They are different but divided into three levels andcorrespond. Both concepts are used to describe the complexity of PCBA assembly,and the level 3 classification is based on the technology used for assembly --through-hole assembly, surface assembly, and hybrid assembly.

These two conceptsdo not quite correspond with reality. On the one hand, plug-in components areused less and less; On the other hand, the difficulty and complexity brought bythe same surface assembly of normal pitch and fine pitch packaging has farexceeded the difficulty and complexity brought by the mixed application of plug-intechnology and surface assembly technology. In other words, the complexity oftoday's electronics manufacturing comes from two main challenges: first,component package sizes are getting smaller; The second is the mixed use ofordinary spacing and fine spacing encapsulation on the same PCB mountingsurface. This is the biggest challenge facing PCBA manufacturability designtoday. The core task of PCBA manufacturability design is to solve the problemof common pitch and fine pitch packaging on the same mounting surface bypackaging selection and component layout and other design means.

Conventional degrees

Mixing degree, animportant concept proposed in this book, refers to the degree of differencebetween various packaging and assembly processes on the PCBA mounting surface,specifically, the degree of difference between the process methods used invarious packaging and assembly and the thickness of the steel mesh, as shown inFigure 1-7. The greater the degree of difference in assembly processrequirements, the greater the degree of mixing, and vice versa. The greater thedegree of mixing, the more complex the process, the higher the cost.