MadSci Network: Computer Science

Re: What materials are my motherboard composed of?

Date: Tue May 16 02:29:33 2000
Posted By: Karl Kolbus, Staff, Data processing, Mequon Consulting Corp.
Area of science: Computer Science
ID: 958407040.Cs

Dear Emliga,
Thanks for the interesting question! While it sounds simple, It seems that 
you may be trying to relate to your students that appearances can be 
deceiving; and you would be very correct. To answer your question, I am 
going to make the assumption that you are not limiting it to the actual 
board, but also to the components mounted upon it. I will also include 
some explanations where the materials may not be readily apparent, and 
will annnotate those materials that are present in trace amounts with the 
suffix (tr.) I will start with the motherboard and follow with the mounted 

Motherboard - fibreglass, phenolic resin, epoxy resin, tin, copper (board 
and cladding and internal power/ground planes/wire traces), tin and 
antimony and/or cadmium, and possibly lead (solder), rosin and/or ammonium 
chloride (flux), brass/gold/silver (contacts), plastic, aromatic solvents 
(tr.) - typically trichloroethylene or acetone(for removing flux), 
lacquer, varnish, paint, ferric chloride (tr.)(residual etchant) and 
various oxides (tr). and sulfates (tr.) resulting from exposure to the 
environment before sealing.  

Components - silicon/fibreglass (component substrates), carbon, 
nickle/chromium wire, high-carbon iron wire(resistors), 
ammonium and/or mangenese chloride(capacitor electrolyte), copper
selenium/chromium/palladium/gallium/silicon/aluminum oxide(transistor and 
diode P-type and N-type junction materials and doping materials, 
gold/platinum/copper(semiconductor internal connections, aluminum indium 
gallium phosphide(or arsenide)(light emitting diodes), lithium/silver
(battery), glass/epoxy resin/rubber/silicone/fibreglass
(encapsulation,insulation), Barium and/or beryllium oxide and silicone 
grease(heat sink heat transfer compounds, Aluminum/steel(heat sinks).

Also, given the various methods of semiconductor growing and laser 
trimming of capacitors and resistors, trace amounts of shielding and anti-
oxididation gases may be present in the form of nitrogen, argon and 
Silver nitrate may also be present as a result of incomplete removal of 
the un-polymerized areas of the board prior to etching. Very briefly, the 
copper-clad board is covered with a photo-sensitive material. A negative 
mask is positioned over the board and the resulting 'sandwich' is exposed 
to ultra-violet light. Those areas where the coating is exposed to the 
U.V. will polymerize, and remain unaffected by the wash with sodium 
carbonate; which removes the un-polymerized coating. Therefore, the un-
polymerized areas will be etched away by the ferric chloride. If your mask 
has very dense blacks AND your transparent areas are very transparent, AND 
your exposure time and intensity is correct, AND your processing solutions 
are fresh AND your processing times are within accepted limits, you will 
end up with a high quality board. If any of the above are not up to 
standard or dust is present in the air, your board may end up with only 
partially etched areas resulting in, at the very worst, short circuits; 
and at the very least, stray capacitances which can adversely affect 
circuit performance; especially at the high frequencies now in common use 
with very fast processors. As you may (correctly) surmisedue to their 
complexity, there is a relatively high rejection rate with motherboards.

I'm sure there are other other materials present due to the rapid changes 
in technology and manufacturing processes, but these are the ones that 
immediately come to mind.

I hope this has answered your question without being too boring 
(considering the level of detail you asked for, and what you got)!

I would be very interested in knowing how you are going to use this 
information, and enjoyed corresponding with someone from a country I would 
very much like to visit. As for myself, I live in Milwaukee, Wisconsin.

You can contact me directly at

Your not-so-mad scientist,

Karl Kolbus

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