Yin_Hsain Koh All these quesions on intermetallics. Wow, I hope you are only 20 years old and can spend the next 40 years getting all of your answers about intermetallics. I have been studying them for 40 years and have metallurgical degree and could only answer a few of your questions. First, intermelallics are compounds of metals that form with specific atomic ratios of these metals in specific crystallographic forms, as opposed to an alloy that is a mixture of several metals. Tin is a great one for forming intermetallics and does with great ease when it is in the molten state or when it is in solid state and in contact with another metal. It forms multiple intermetallics with copper, nickel, gold, palladium, bismuth, silver and many others that are not of great interest to the PCB industry. Lead also forms some with palladium. If you look at the phase diagrams books, they usually have the additional data such as the crystallographic size and shape and atomic ratios such as Cu6Sn5 and Cu3Sn. If you have and accurate phase diagram and a X-ray diffraction unit (not EDAX) you can determine which intermetallics you are looking at by measuring their size and crystal arrangment and then looking up to see which one you have. If you are smart with your metallographic techniques and have a SEM, or a good optical, you can often see the different layers of intermetallics in the solder joint extending from the non-fusible metallic surfaces. All of the intermalllics have different strengths, fracture resistance or ductility and you usually cannot change that. This will contribute to the capability of you solder joint to withstand stresses. Additionally, as the temperature increase, greater thicknesses of the intermetallics form and different intermetallics may form. There are many good studies that have been made on specific intermetallics such as tin/gold, but I do not know of any one book that covers the range you are looking for. International Tin Research Institute located in the UK, London I think, has published many articles on the tin componds. Many of the soldering books have vague information about intermetallics, mainly they leave you with the feeling if you form intermetallics it must be a bad solder joint. In reality, you must form intermetallics to have a tin-solder alloy type solder joint. Many authors who write wildly about intermetallics do not know if "intermetallic" is spelled with one "L" or two "LL's". I will not say more, but it is a very complex subject and I wish you luck. Phil Hinton