2
\$\begingroup\$

If I were to make a make a footprint, even for a simple component like a 0603 cap, and the manufacturers recommendation differs from IPC-7351, would it be recommended to start with the manufacturers footprint or the IPC footprint? A very specific example is the TDK C1608X5R1A475K080AE where TDK would have me make a pad that is 0.6~0.8 mm wide and IPC-7351 would have me make a pad that is 1.0 mm wide, with differing lengths as well.

In the end, I would think that a lot of influence for this decision would come from the CM (contract manufacturer) that is holding the ball with respect to assembly reliability but without CM input, what is the general thinking on a good starting point.

Bias: Sometimes I wonder what good IPC is as I interpret it as simply collecting and dissemination information about existing practices and by definition, always behind the curve on assembly techniques. None the less, I am still looking for a comment or opinion on my question.

\$\endgroup\$

3 Answers 3

2
\$\begingroup\$

For chip components like 0603 and smaller I would avoid IPC's recommendations. In the IPC's "Nominal Density" condition the toe is way too big which can increase the torque on the solder joint which eventually can lead to more tomb-stoning. If you want/have to stick to IPC, you should at least choose the "Least Density" condition which results in slightly smaller pads (and toes).

However, the first choice for chip components like 0603 and smaller should be the recommendation of your CM. If you want to stay more generic, the second choice should should be the recommendation of any reputable manufacturer (or the "mean" between several reputable manufacturers).

Standard IC packages are usually way less critical. IPC recommendations should be fine in most cases. For any special IC packages I would stick to the manufacturer's recommendation.

In any case: Speaking with you CM is always a good idea.

\$\endgroup\$
1
\$\begingroup\$

IPC is a "generic" standard, so it is specified to work with all products that fit in the relevant category. An engineer, having designed a device and knowing its properties can make a specific plan that is adequate to the product in question.

\$\endgroup\$
4
  • \$\begingroup\$ Thanks, but what I was really hoping for was to hear from someone that had a specific experience that clearly drove the decision of footprint choice in one direction or another. An example might be how a a problem like cracking or solder adhesion was fixed or made worse by a particular choice. \$\endgroup\$
    – Ken
    Commented Jan 29, 2021 at 15:44
  • \$\begingroup\$ Or, to put it another way, when does IPC-7351 fail and when does IPC-7351 really shine. \$\endgroup\$
    – Ken
    Commented Jan 29, 2021 at 17:04
  • 1
    \$\begingroup\$ Usually you could assume the manufacturers footprint, if differing from IPC-7351, was modified for some good reason. Maybe you do not know the reason, or it does not apply to your case or application area. If in doubt, ask an assembly engineer. I think IPC shines for standardized components, layouts, packing densities, so where nothing is near extremes... I often modify footprints for improved isolation distance, higher layout density, and to solve specific soldering difficulties in serries production caused by footprints (from manufacturer or IPC alike). \$\endgroup\$
    – datenheim
    Commented Jan 1, 2023 at 11:51
  • \$\begingroup\$ @K H: so you recommend to trust the manufacturer more than IPC!? \$\endgroup\$
    – datenheim
    Commented Jan 1, 2023 at 11:58
0
\$\begingroup\$

Some notes moreso than an answer, but too long for comments:

IPC is an industry trade association; many standards are indeed just that [dissemination of existing practice]!

Much of it is also recommendation; you can say something is "IPC compliant" but it doesn't actually mean much when you look closely at what is "required" and what is "recommended".

The standards are most useful, I think, in terms of introducing a topic -- providing a framework in which to understand those practices; how things are measured, terminology, worked examples. Most powerfully, perhaps, is to begin to understand how and when to break them [rules or recommendations]; or at least, how you could go about evaluating the value of breaking them (for example, statistical study of production yield for some odd case).

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.