IEC 60749-39-2021 Semiconductor devices – Mechanical and climatic test methods – Part 39: Measurement of moisture diffusivity and water solubility in organic materials used for semiconductor components.
6.1 Sample preparation
6.1.1 Process and cure the samples using recommended processing conditions in
accordance with the manufacturer’s specification.
6.1.2 To obtain the appropriate sample thickness as given by Formulae (1 ) or (2), samples can be sectioned and finely polished from larger specimens. Near parallel-sided flatness shall be maintained for samples prepared in this manner.
The prepared samples should be inspected for voids, both internal and surface, using acoustic microscopy or x-ray. The ideal samples should be nearly void-free.
6.2 Absorption measurements below 1 00 °C
6.2.1 Measure the linear dimensions of the prepared sample to the nearest ±0,02 mm. Record the sample thickness, h, and calculate the sample volume, V, using the appropriate geometric relationship based on the sample shape.
NOTE Calculating the volume by measuring the linear dimensions is never accurate. The error is smaller when the sample is big. One accurate way of determining the volume is to use Archimedes’s principle, which is to measure the sample weight in air and immersed in a liquid with known density (ethyl alcohol, IPA, etc.). In this way, the volume of a sample with irregular shape can also be determined.
6.2.2 The dry weight of the sample shall be determined, in accordance with IEC 60749-20, firstly by baking the sample for 24 h at 1 25 +5/-0 °C and continuing to bake and weigh the sample every 1 2 hours until no further weight loss is observed to ensure that the sample(s) are dry. The dry weight is determined when no further weight loss is observed, less than 0,002 % difference, after two consecutive measurements with a minimum baking interval of 1 2 h. Within 30 minutes after removal from the oven, weigh the sample(s) using the analytical balance equipment described in 4.1 and determine the dry weight in accordance with 6.2.4. In accordance with IEC 60749-20, small sample(s) (less than 1 ,5 mm total height), devices should be weighed within 30 minutes after removal from oven.
6.2.3 Remove the sample from the bake oven and immediately cool by placing in contact with the heat sink of 4.5. If more than one sample is to be measured, the samples and heat sink should be placed into a desiccator to limit moisture uptake during the mass measurements.
6.2.4 Weigh the sample using the balance described in 4.1 and record the mass as M Comp,dry,1 . Read points: At the desired read point; remove the sample(s) from the bake oven. Within 30 minutes after removal of the sample(s) from the bake oven, remove the sample(s) from the container and determine their weight using the analytical balance equipment in 4.1 . Within 30 minutes after weighing the samples, place them in a clean, dry, shallow container so that the sample bodies do not touch each other. Return the sample(s) to the bake oven for the desired time. Continue until the sample(s) have lost all their moisture as determined by the dry weight in 6.2.2.
6.2.5 Place the sample(s) into a stainless steel holder and transfer to a temperature/humidity chamber stabilized at a pre-set temperature and humidity. The sample should be transferred into a stainless-steel holder that has been preheated and stabilized to the set chamber temperature.
6.2.6 At accumulative times, remove the sample from the temperature/humidity chamber, cool and measure the sample mass in accordance with 6.2.4. Record the mass as M Comp,wet,t .
6.2.7 Read Points: The X-axis (time) read points, in accordance with IEC 60749-20, are selected for plotting the absorption curve. For the early readings, points should be relatively short (24 h or less) because the curve will have a steep initial slope. Later readings can be spread out further (1 0 days or more) as the curve becomes asymptotic. The Y-axis (weight gain) should start with ‘‘0’’and increase to the saturated weight gain. Most sample(s) will reach saturation between 0,3 % and 0,4 % when stored at 85 °C/85 % RH. Devices shall be kept at room ambient between removal from the oven or chamber and weighing and subsequent reinsertion into the oven or chamber. Ensure that no condensed moisture from the chamber walls comes into contact with a sample during removal from the temperature/humidity chamber. If condensed water should contact a sample, immediately dry the sample using nitrogen or dry air.
The sample should then be returned to the chamber for re-equilibration and another data point taken at a later time. The sample weight measurement shall be made within a few minutes after removal of the sample from the temperature/humidity chamber. Time delays longer than 5 minutes after removal from the temperature/humidity chamber could affect the sample weight measurements.IEC 60749-39 pdf download.