ADVANTAGES AND LIMITATIONS OF PEMs

Lower cost is normally the chief advantage cited for the use of PEMs over HSMs, especially as the number of inputs/outputs increases. However, this cost savings is only realized if the product is manufactured in a high volume commercial/industrial flow, and will diminish rapidly if additional tests and screens are added, as is typical of military HSMs. A common error in cost analysis is to project military PEM cost savings based on, for example, multimillion automotive volumes. PEMs are manufactured at 20X the volume of HSMs. A benefit to this is that these high volumes are accomplished through automation (as opposed to the more hand-oriented manufacturing of HSMs), which greatly reduces handling damage and process variability. PEMs, having a solid molded construction, are mechanically more rugged and weigh substantially less than HSMs. PEMs employing surface mount technology (SMT) offer a significant advantage over HSMs in terms of reduced size and weight. SMT is the predominant choice for most system applications today. Therefore, more than a cost benefit can be realized with the careful selection of PEMs. The most often cited concern about PEMs is their non-hermetic nature and permeability to moisture. Although this will be covered in more detail in a later section, it is stated here that major advancements in PEM technology have been made over the past decade, such that moisture induced failure mechanisms are not a major issue in most applications today. A composite listing of the advantages and limitations of PEMs relative to HSMs are presented below.

Advantages of PEMs Relative to HSMs:

 

Limitations of PEMs Relative to HSMs: