Solderability Testing

"Solderabilty Testing" is a process to evaluate the usability of a solderable component with respect to quality and reliability.

With the passage of time, a?passive solderable component may lose its property of getting soldered into the electronic circuit. This is sometimes defined as “ Expired Self Life”. At this point , component is tested for its soldering i.e. Solderability test and if the component passes the test , it is treated as Usable. ?

There are few standard which talks about the Solderability Testing.These standards are:

a)????Mil-Std-883 Method 2003 - "Solderability"

b)????IPC/JEDEC?J-STD-002 - "Solderability Tests for Component Leads, Terminations, Lugs, Terminals and Wires"

c)????IPC/JEDEC J-STD-003 - "Solderability Tests for Printed Boards"

d)????JESD22-B102

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Before going into details of the practical testing, lest us understand three relevant term related to this.

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Wetting: Solder wetting is a phenomenon , where the solder forms a uniform, smooth and unbroken film of solder metal over the solderable surface e.g. Component Leads, Terminations, Lugs, Terminals and Wires.This phenomenon exhibit rather proves to have an excellent adherence of the solder metal over the surface.

Non-Wetting: This is phenomenon where the solder does not adhere to the surface completely, rather partial adherence. Few areas are covered with solder but few remains exposed, means solder did not stick to entire area.

De-Wetting:In this phenomenon ,solder recedes after coating the surface resulting uneven and irregular surface. Here the surface can been seen with irregular mounds of solder and contrary to the non-wetting , no area is exposed ( i.e. no area without solder coating).

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In order to understand these three technical term in a simple way following can be said.

Dip a piece of dry iron rod into a glass of water and take it out. You will see , it is completely and uniformly wet…this is wetting. Now just add thin layer of oil onto this rod and dip it again…you will see water is sticking at selected location and no water in few areas….…it is called non-wetting. Now dip a painted piece of the rod, you will see rod is wet but droplets are sticking to few places….this is called de-wetting. Now you can co-relate the tern and can take your judgement to understand the phenomenon.

There are two most common ways to test the solderability:

1.????Wetting Balance test

2.????Dip and Look method.

?In wetting balance test, wetting force is measured which is imposed by the molten solder on the test surface. Higher the force better is the solderability as a thumb rule. Apart from this there are other parameter like dip time, wetting time and so to conclude the final result. This test is basically used as an engineering tool not because it is difficult to execute but also due to lack of clarity in the result analysis i.e. no industry standard is established for pass and fail criteria.

On the other hand ?“Dip and Look” is widely used in Process Quality Assurance as well as ?in Reliabity Assurance Process.Here the decision is made based on physical and Visual attributes of the sample.

How to carry out “Dip and Look “ testing?

?The test starts with the sample preparation where it is ensured that the soldering terminal under the examination must not be cleaned in any manner viz. wiping, cleaning, scraping, or abrasive cleaning.Now the sample is treated in Salt Spary Chamber for at least 24 hrs under the humidity of 95% and temp 35 degree .This 24 hrs under the chamber is done to simulate the ageing of the component to take into consideration the natural aging effects of storage prior to board-mounting.Now the component is dried either in a chamber at 100 degree for more than an hour or put into the dry cabinet for 24 hrs .Next,the flux ?is ?properly applied onto the terminal under examination. Now a static solder pot filled with molten solder is taken, where the temperature is controlled at 240 to 250 degree C. Now the sample is dipped into the pot with the controlled downward and upward movement meaning the sample is dipped into the pot with uniform speed and pulled out the sample from the pot with same uniform speed. Now the sample Dipping is complete.

After this process, the sample is examined under the 40 X ?microscope and and the termination is observed for clean and shiny surface. In technical term sample should not exhibit the phenomenon of non-wetting and De-wetting. ???

??Now if the sample does not exhibit non-wetting and de-wetting phenomenon the sample is treated as PASS in “DIP and LOOK TEST".