I need to provide clarification to a few issues in this e-mail from the 
technical committees of the IPC.

>From the IPC-T-50E Terms and Definitions, comes the following industry 
definitions:

Solder Connection Pinhole - A small hole that penetrates from the surface 
of a solder connection to a void of indeterminate size within the solder 
connection.

Blow Hole - A void cause by outgassing.

Regarding Thermal Stress:  A hot oil float at 500 degrees for 30 seconds 
should not damage a good quality hole.  Many companies do multiple 10 
second floats at 550 on solder. One company local to Chicago tried a 600 
float for 10 seconds after treating their copper plating bath. In IPC 
Post separation minitest program test, we used multiple floats, high temp 
to CO2 cold cycling and were unable to get good holes to fail.  In 
IPC-TR-579 we used hot oil 550 for 20 seconds, fluidized sand at 550 for 
20 seconds cycled to water at room temp.  Good boards survived all of 
these stress. Now I would not recommend these tests for production, but for 
process control or for design verification they are handy.

Regards

***************************************************
David W. Bergman, Technical Director
IPC
2215 Sanders Road
Northbrook, IL  60062-6135
708-509-9700 x340 Phone
708-509-9798 Fax
email  [log in to unmask]
***************************************************


On Mon, 23 Oct 1995, MR NORMAN S 
EINARSON wrote:

> A previous debate on delamination/baking boards sparked a response 
> from Robert Willis from the UK, realative to pin holes/blowholes in 
> solder connections.
> 
> Robert Willis stated:
> 
> "Blow holes are not caused by component terminations or poor wetting 
> of the plated through hole.  If anyone thinks this they are 
> misunderstanding what the term pin hole or blow hole is."  This is 
> such a strong statement it forced me to add my two cents to his 2 
> pence.
> 
> I will qualify my response by stating that I have performed and/or 
> evaluated thousands of micro sections of plated through holes in my 
> 30 years in this business.  This includes both the populated and 
> unpopulated board.  Let's first define pin holes and blow holes in a 
> solder connection.
> 
> Pin Hole:    A pin hole is a depression in a solder connection, 
> whereas, the bottom of the depression is visible after cleaning.
> 
> Blow Hole:   A blow hole is a void in a solder connection, whereas, 
> the bottom of the void is not visible after cleaning.
> 
> Without a sketch, this is the best definition.  A pin hole is 
> generally caused from a small plating void in the copper plating of a 
> PTH.  It can also be caused from flux entrapment in the hole, whereas,
>  the pre-heat did not drive all of the volitiles from the flux 
> (improper control of pre-heat) prior to entering the wave.  In the 
> case of copper plating voids, gasses are allowed to escape into the 
> hole area.  With either flux entrapment or plating voids, a small gas 
> bubble will expand with heat and contract upon cooling, thus, pulling 
> the surface solder back into the hole in the form of a pin hole in 
> the solder connection.
> 
> A blow hole is caused from a wetting problem with either the 
> component lead or the copper hole wall.  It can also be caused from 
> larger plating voids, which ultimately is also a wetting problem 
> because you can't wet solder to epoxy glass.  Obviously, larger voids 
> will allow more gasses into the hole area that may result in larger 
> pin holes or blow holes.  However, my experience through micro 
> sectioning of the holes has shown a wetting problem 90% of the time.  
> The other 10% was either very large plating voids or an evaluation 
> could not be made.
> 
> Mr. Willis mentions the involvement of the National Physics Lab in 
> the UK, realtive to a study of outgassing.  Many years ago (10 - 20), 
> I received a copy of this study before it was totally complete.  The 
> study showed considerable outgassing in the hole after the 
> electroless copper process.  This was a reasonable conclusion as 
> electroless copper is only 75 to 100 micro inches thick and very 
> porous.
> The study further showed that outgassing, if any, was very minimal 
> after copper electroplating to the required thickness.  They also 
> mentioned outgassing from the surface of the board where the surface 
> copper is only 80 - 85% covered with copper.  Certainly, this all 
> makes good common sense.
> 
> Pin holes are of little concern, relative to quality issues, and 
> should not be touched up with a soldering iron.  The old saying, " 
> keep the the iron off the board surface unless it is absolutely 
> necessary", certainly applies here.  The use of hand irons, if the 
> process is not totally adhered to, will rapidly destroy good holes.  
> When pin holes are evident, the source of the problem should be 
> investigated and eliminated.  Though it is not a quality issue, it 
> should not be ignored.
> 
> Blow holes can be a serious reliability issue, as you don't know the 
> extent of the blow hole without destructive testing.  However, here 
> again it must be stated that blow holes should not be touched up.  
> Again, find the source of the problem and eliminate the problem.
> 
> Concave or sunken solder joints:  You will find that sunken or 
> concave solder joints are generally caused from barrel cracks.  This 
> is a very serious reliability issue and should be further 
> investigated.
> 
> Let's assume that your fabricator plates your required copper 
> thickness in the holes (.001" min.), without any voids.  I find it 
> very difficult to believe that gasses can pass through a solid shield 
> of .001"  thick copper in the 3 to 4 seconds that the board is 
> exposed to the wave solder pot, unless there was plating defects.  
> This only makes good common sense!
> 
> We all know that the board material is hydroscopic and absorbs 
> moisture to some degree.  However, it is a small percentage of the 
> total weight.  When viewing a micro section with blow holes in a 
> microscope, either the component lead or hole wall will evidence 
> absolutely no solder coating.  This is either dewetting or nonwetting.
>   Though there is some moisture in the material, it would require a 
> high pressure steam hose to clean the areas shown as not wetting in 
> the scope.  If you don't believe this, do your own micro section the 
> next time you see a blow hole.
> 
> Mr. Willis did a good job explaining his process of testing for voids 
> or thin plating, with the use of oil in the hole and heating it up.  
> I think most people agree that touch of solder connections with a 
> soldering can create far more problems than it would cure.  To 
> perform the oil test as descibed by Mr. Willis would require 500 
> degrees "F" for 30 seconds on the board surface.  I submit that this 
> would destroy good boards.  I may also suspect that this temperature 
> and time could crack plating barrels and lead you to believe that you 
> had defective boards, when it could be the test itself causing the 
> problem.  Basically, whenever using a hand iron, you must get on the 
> connection with the iron and off again before the epoxy surrounding 
> the hole has a chance to completely expand.  This generally leaves 1 
> to 1-1/2 seconds to complete a hand soldering process.  This includes 
> soldering and desoldering.
> 
> It appears to me that if you are going to use Mr. Willis' oil test, 
> you should ask your fabricator for scrap boards from the same lot for 
> test purposes.  Don't destroy god boards!
> 
> At its best, I think you could use the oil test as an indicator of 
> plating voids and very thin copper plating.  IPC-RB-276 allows voids 
> in Class 2 and no voids in Class 3.  Except in very isolated cases, 
> voids will seldom be an issue today.  In fact, most vendors will 
> admit that if voids are evident, there is a process control problem.
> 
> Norm Einarson
> PRINTED CIRCUIT TECHNOLOGY    
>    
> 
> 
> 
>