SMT007 Magazine


Issue link:

Contents of this Issue


Page 13 of 92

14 SMT Magazine • July 2014 dering. It is manifest as a circumferential tear of the copper land to which a component, nor- mally a BGA, is assembled. h) Decomposition: Decomposition of a PCB is a relatively new phenomenon associated with higher temperatures used with lead-free soldering. In fact, a new term was added to the industry lexicon, T d , which is the temperature of decomposition representing a loss of a specified percentage of the weight of the printed circuit. Clearly, printed circuit technology, like sol- dering technology, is fraught with its own vul- nerabilities due to the complexities of process- ing. The demands on PCB technology foisted upon the industry by the imposition of lead-free soldering requirements have placed a heavy bur- den on the printed circuit manufacturing indus- try. The need for higher glass transition tempera- tures to assure a measure of survival through the elevated temperatures of lead-free soldering has required the printed circuit industry to qualify new materials. Simultaneously, there has been a demand placed upon the industry to remove halogenated flame retardants from its materials. This double-barreled challenge is one that the industry had not faced before. Moreover, the in - dustry has been challenged to provide circuits with ever-finer features which operate at ever- increasing frequencies. To their credit, printed circuit industry tech- nologist, engineers and scientists have struggled admirably to address these challenges, includ- ing the challenge of finding solutions to defect modalities that were unknown to the industry just a few years ago. Unfortunately, a number of the defects described are related to solder- ing and its effects. The earlier problems have been exacerbated by the increased temperature required for lead-free soldering. Figure 2 offers cross-sections of representative printed circuit defects resulting from thermal excursions. Solderless Assembly for Electronics (SAFE) Technology: A Simpler Approach? Given all the challenges and risks associated with soldering, every thoughtful and prudent manufacturing engineer must constantly be seeking a way or ways to make assembly pro- cessing more robust. If one looks for inspiration on how they might end their dealing with the devil, they can find it in the Bible, where it is written: "If thine eye offend thee, pluck it out, and cast it from thee." Perhaps this is a bit ex- treme, but this seems to be where the industry is stuck today in dealing with the devil. Solder is by analogy an offending element of manufac- turing and source of many if not most manufac- turing problems. The industry will continue to have to deal with that devil as long as we persist in its use. One can do their own research to test this assertion if they choose. They need look no fur- ELECTRoniC inTERConnECTionS ElECTRoNIC ASSEMBly WITH SolDER continues figure 2: Cross-sectional micrographs of printed circuit defects caused by soldering are provided above. Clockwise from the upper left-hand cor- ner: corner crack, barrel crack , pad lifting, post separation, pad cratering ,hole wall pull away, resin recession and delamination.

Articles in this issue

Archives of this issue

view archives of SMT007 Magazine - SMT-July2014