Tom
11-03-2002, 12:00 PM
IPC Advanced Study Guide Page Reference: Pages 25 & 30 Section 1.3
Cleaning is also a consideration that must be reviewed when determining surface finishes and assembly operations. The cleaning of surface mount assemblies is usually a little more difficult than the conventional through-hole due to the smaller gaps between surface mount components and the board itself. These smaller gaps may entrap flux which may cause potential reliability problems if the printed board is not properly cleaned and the flux has conductive or corrosive properties.
The cleaning process being used depends on the spacing between components, terminations, and the height that the component sits off the printed board assembly. One of the reasons why BGAs became so popular is that the ball and the ball size automatically provide a standoff that will help promote the cleaning of flux and flux residue. A recommended standoff height for components in order to facilitate proper cleaning has been developed. This height is based on the component surface area that would permit any cleaning solution to move underneath the part.
There are also no-clean fluxes. The flux residue is not corrosive nor conductive and is left on the board.
Room for cleaning is based on the component size. Aqueous cleaners with saponifiers are used in many applications to remove any contamination. Standoff height is shown in the following table.
Cleaning is also a consideration that must be reviewed when determining surface finishes and assembly operations. The cleaning of surface mount assemblies is usually a little more difficult than the conventional through-hole due to the smaller gaps between surface mount components and the board itself. These smaller gaps may entrap flux which may cause potential reliability problems if the printed board is not properly cleaned and the flux has conductive or corrosive properties.
The cleaning process being used depends on the spacing between components, terminations, and the height that the component sits off the printed board assembly. One of the reasons why BGAs became so popular is that the ball and the ball size automatically provide a standoff that will help promote the cleaning of flux and flux residue. A recommended standoff height for components in order to facilitate proper cleaning has been developed. This height is based on the component surface area that would permit any cleaning solution to move underneath the part.
There are also no-clean fluxes. The flux residue is not corrosive nor conductive and is left on the board.
Room for cleaning is based on the component size. Aqueous cleaners with saponifiers are used in many applications to remove any contamination. Standoff height is shown in the following table.