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February 2010

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From:
Gary Ferrari <[log in to unmask]>
Reply To:
Date:
Tue, 23 Feb 2010 13:03:01 -0500
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Jon,

I recommend that you read IPC-2615, Printed Board Dimensions and 
Tolerances. It explains, and illustrates, geometric dimensioning and 
tolerances, as it applies to printed boards.

Gary

On 2/23/2010 11:58 AM, Roberts, Jon (SA-1) wrote:
> 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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