Something else to consider - will the end product be fixed at the component
level or board level.  Meaning, if the board fails in the field or back at
the shop, will a tech be expected to fix it at the component level or just
toss the entire board and put in a new one.  Maximum pad is necessary for
desoldering and resoldering parts, reduces the chance of pads lifting off.


Dee Stover  [log in to unmask]
Design Drafting Technician
National Optical Astronomy Observatory



At 04:56 PM 9/22/1999 +0100, you wrote:
>Dear all,
>
>All the data I have regarding pad sizes (e.g. IPC-2221 9.1.1) give examples
>on how to calculate Minimum pad sizes, usually from a PCB fabrication
>standpoint. IPC-2221 states that all lands and annular ring shall maximised
>wherever feasible, consistent with good design requirements and electrical
>clearance requirements.
>
>My questions are: How do I determine the pad size that will give me the best
>soldered joint?
>Would the minimum pad size calculated by the formula in section 9.1.1 still
>provide a good soldered connection?
>Are there upper limits to the size of a solderable surface of a pad?
>Would the Ideal be to maximise all the pad sizes to one size that meets the
>requirements of 9.1.1 for all holes?
>
>I am surprised there is no reference to soldering in the standard relating
>to pad sizes, I am sure the pad size must have some effect on the solder
>fillet.
>
>
>Thanks in advance,
>
>Mark
>
>