Thanks for all your help and I could not find the definition of MMC or
LMC in IPC 2222 but found Effective Training Inc from searching internet
which explained those acronyms (The pictures/figures did not copy. Is
these the correct definitions?

From Effective Training Inc website:

Introduction to Bonus Tolerance

Bonus tolerance is an important concept in dimensioning parts. Bonus
tolerances can reduce manufacturing costs significantly. This section is
an introduction to the bonus tolerance concept. 
Definition 
Bonus tolerance is an additional tolerance for a geometric control.
Whenever a geometric tolerance is applied to a feature of size, and it
contains an MMC (or LMC) modifier in the tolerance portion of the
feature control frame, a bonus tolerance is permissible. 
This section introduces bonus tolerance based on the MMC modifier. When
the MMC modifier is used in the tolerance portion of the feature control
frame, it means that the stated tolerance applies when the feature of
size is at its maximum material condition. When the actual mating size
of the feature of size departs from MMC (towards LMC), an increase in
the stated tolerance- equal to the amount of the departure - is
permitted. This increase, or extra tolerance, is called the bonus
tolerance. 
Figure 3-16 shows how bonus tolerance is calculated in a straightness
application. When the MMC modifier is used, it means that the geometric
characteristic can be verified with a fixed gage. 
A functional gage is a gage that is built to a fixed dimension (the
virtual condition) of a part feature; a part must fit into (or onto) the
gage. A functional gage does not provide a dimensional measurement; it
only indicates if the part is or is not to the print specification. 
 
Figure 1 
In Figure 1, the functional gage is designed to the virtual condition
(2.7) of the feature of size. Since the gage opening is constant, the
thinner the washer becomes, the more straightness tolerance it could
have and still pass through the gage. 
Although a straightness control is used for the example in Figure 1, the
bonus tolerance concept applies to any geometric control that uses the
MMC (or LMC) modifier in the tolerance portion of the feature control
frame. 
 
Figure 2 
Figure 2 shows how to determine the amount of bonus tolerance
permissible in an application. The MMC modifier in the tolerance portion
of the feature control frame denotes that a bonus tolerance is
permissible. The maximum amount of bonus tolerance permissible is equal
to the difference between the MMC and the LMC of the toleranced feature
of size.  Definition 
Bonus tolerance is an additional tolerance for a geometric control.
Whenever a geometric tolerance is applied to a feature of size, and it
contains an MMC (or LMC) modifier in the tolerance portion of the
feature control frame, a bonus tolerance is permissible.



-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Gary Ferrari
Sent: Tuesday, February 23, 2010 10:03 AM
To: [log in to unmask]
Subject: Re: [TN] LEAD TO HOLE RATIO QUESTION

Jon,

You don't relate them to reliability classes. Levels are producibility 
indicators. The table makes recommendations that would provide for an 
acceptable solder fillet for all classes.

Gary

On 2/23/2010 10:36 AM, Roberts, Jon (SA-1) wrote:
> How do you relate the Levels (A, B,&  C) to IPC Classes 1, 2&  3?  We
> design and build assemblies for Army ground vehicles and contract
state
> to use IPC Class 3 standards.
> I keep thinking I remember that 0.017 was nominal back in the 80s.
> Thanks for all the help, Jon
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Gary Ferrari
> Sent: Tuesday, February 23, 2010 9:09 AM
> To: [log in to unmask]
> Subject: Re: [TN] LEAD TO HOLE RATIO QUESTION
>
> Jon,
>
> You will find the information you are looking for in IPC-2222A Table
> 9-3.
>
> Gary
>
> On 2/23/2010 9:45 AM, Roberts, Jon (SA-1) wrote:
>> I was trying to find in IPC 2200 series where the lead to hole ratio
> is
>> discussed.  I remember we would provide to contractor instructors the
>> requirements. That is going back to the WS5626 days.  Can you direct
> me
>> where to find that information.  I am looking for double
> side-multilayer
>> boards for meeting Class 3 of IPC J-Std-001.
>>
>> Thanks, Jon
>>
>>
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