D-MAX DMC-20SEC Manual de usuario descargar pdf (Pagina 6)

6.1. Solder paste inspection

According to PWB assemblers, it is very important that the quality of the print solder paste is

inspected because it heavily influences the quality of solder joints. In some papers it has been

reported that 52%–71% of SMT defects are related to the printing process [50]-[53]. As failures

can be detected much earlier, this obviously results in cost savings. According to some other

opinions, inspection of the solder paste is not so relevant: “Contrary to the common, frequently

quoted opinion that paste faults represent the primary percentage or 70% of all faults in the

printed circuit assembly process, this detailed analysis shows that those faults amounted to

only 8.3%.” [54].

Special AOI machines are able to inspect the quality of print of the solder paste. It is an important

option because in case of failure, the product can be repaired with minimum cost and with‐

out scrap loss. The size of the print in the 3 dimensions examined (latitude, longitude, alti‐

tude) must fall within the limits specified. To measure these parameters, so-called SPI (Solder

Paste Inspection) machines have been developed. These machines are able to inspect only one

step i.e. paste printing, but they are cheaper than universal AOI machines. As the control of

solder paste presence is one of the easier tasks, then only the width, length and position needs

to be inspected and so several failures can be detected such as bridges [55]. This can be solved

using image capturing (usually with the help of line scan cameras) and subsequent evaluation.

But to measure volume as well the paste thickness is equally as important. Comparison

between 2D and 3D solder paste inspections are reported in [56] and [57]. There are several

possibilities to enable the measurement of paste volume optically: laser scanner [58]-[63];

projected sinusoidal fringe pattern as in [64]; the development of this technique for solder paste

geometry measurement in [65], [66] and some special methods shown in [67]-[69]. Nine

manufacturers offer SPI systems [70]-[82]. Several different solutions have been developed in

these appliances as can be found in the scientific literature, described above. Comparison

between the different methods is shown in Table 2.

Figure 3. Possible places of AOI systems

Materials Science - Advanced Topics

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D-MAX DMC-20SEC Manual de usuario Pagina 6