A cursory review of relevant articles by certain experts seems to confirm this statement. They think about how the environment can influence machines and products without saying a word about the workers who work on the production line under these conditions.
But perhaps this is not so unusual. Because although the trade unions insist on a low-noise environment - ear protectors are required by law for working in noise above 95 dB - their members go to a 'heavy metal' concert at the weekend, stand two meters in front of the oversized loudspeakers and let themselves be blasted with 110 dB(A), which could actually already be punished as bodily harm [2].
As sound has hardly any influence on the printing of solder paste, experts in the electronics industry prefer to focus on other aspects of production facilities. Temperature and humidity are at the top of the list, while air pollution is rarely mentioned. After all, companies have set up special smoking areas or you can see the ladies and gentlemen shivering outside the door with their tobacco pipes.
Scientists and, of course, manufacturers of air conditioning and heating systems have studied in detail the concept of comfort and the external circumstances that indicate the conditions under which a person feels comfortable. ANSI/ASHRAE Standard 55[3] (Thermal Environmental Conditions for Human Occupancy) has been developed, and in some ways defines the conditions that should be considered comfortable for an indoor environment. The American Society of Heating, Refrigerating and Air-Conditioning Engineers issued the first version in 1966 and has been updating it since 2004. The latest edition is currently dated 2017.
Such commercial specifications, of course, hardly seem to have found their way into the standards of the IPC, for example. There are several that deal with temperature and humidity, each of which is geared towards the various production processes - from storage and packaging to transportation and general production. A careful distinction is made between the unfinished product and the individual parts as well as the finished product, as these have their own sensitivities.
J-STD-001F (Requirements for Soldered Electrical and Electronic Assemblies) states in § 4.2.1 under 'Environmental Controls': The soldering hall should be enclosed, temperature and humidity controlled and pressurized. In § 4.2.2 it becomes even clearer: The humidity should be kept between 30 and 70 % relative humidity, the temperature between 18 and 30 °C.
Fig. 2: Drying storage cabinet 'Super Dry' from Totech
Fig. 3: Ströbel indicator strips for moisture absorption
A quick glance at Fig. 1 shows that the workers probably wanted to change their clothes more often at 70 % relative humidity and 30 °C. The reason for such values is derived directly from the product, which is exposed to increased susceptibility to electrostatic discharge outside these ranges. IPC-A-610 F (Acceptability of Electronic Assemblies) is more or less along the same lines. But ESD (Electrostatic Discharge) is not the only concern of the committee members of these bodies. They are concerned about the manufacture of components and printed circuit boards right through to the final packaging, as temperature and humidity are also issues that need to be discussed during the production of the printed circuit board. For example, prepregs [4] should be stored flat, cool and dry <23 °C, <50 % RH, which is still acceptable. After all, this is certainly in a cupboard that workers are unlikely to stray into.
The biggest concern, however, is the interaction between pastes and ESD, which is somewhat surprising. But with a little thought, you quickly realize that what is good for pastes is usually bad for static electricity, so a compromise should be found as to what climate can now be maintained in the factory floor. The importance of such decisions can be demonstrated with dollars and cents. What companies spend on protection against ESD damage[5] reflects the costs that would be expected should such damage actually occur. Estimates for actual damage are around $5 billion. Expenditure on precautions taken by companies is in a similar range.
References
[1] 'Zuerst kommt die Produktion, dann der Mensch', short documentary film, BRD 1972/1972, BRD1971/1972Short documentary film, directed by Günter Hörmann.
[2] www.welt.de/print-welt/article334313/Vom-Ticken-der-Uhr-bis-zum-Presslufthammer.html (Retrieved: 16.12.2024).
[3] en.wikipedia.org/wiki/ASHRAE_55 (Retrieved: 16.12.2024).
[4] preimpregnated fibres - pre-impregnated fibers
[5] Report 'Circuit Protection Market' from the year 2022: www.marketsandmarkets.com/Market-Reports/circuit-protection-market-156298269.html (Retrieved: 16.12.2024).
