Dueto the implementation of the Restriction of Hazardous Substances (ROHS),various lead-free solders have emerged in the PCBA processing industry.
SnAgCu(SAC) alloys are the most common choice due to their excellent physical,mechanical and fatigue properties and acceptable soldering methods and costs.
However,as shown by the drop test results, the application of such alloys is inherentlyinadequate due to the high brittleness of the solder joints (relative to63Sn37Pb).
Thisis especially important for portable products in array packages such as BGA andCSP.
TheSAC solder joint breakage mainly occurs at the interface between the solderpaste and the pad.
Obviously,any problems that occur at the interface can be solved by taking measures onone or both sides of the interface (such as pad metalization and solder alloy)or by reducing the impact on the solder joints.
Otherways to improve solder joint reliability are:
1）Improve surfacetreatment
2)Strengthen the connection force
3)Improve packaging
1.Improving Surface Treatment
Thesurface treatment components directly affect the type of IMC formation. It isknown that in some cases, the drop test performance of a nickel gold pad isinferior to that of an OSP. This situation seems to be related to the formationof coarse-grained IMC scallops on nickel. If the thickness of the coating isnot controlled within the range of 0.2 μm, the drop test results of theimmersion silver will also be affected by small voids.
2.Strengtheningthe Connection Force
Thefragility of brittle solder joints can be compensated by the use of adhesives.Adhesives increase the strength of the connection between the BGA and the PCB.Common methods are capillary underfill and corner reinforcement points. Thedisadvantage of bottom filling is that there are many steps, and the fluxresidue affects the adhesion, but the advantage is that the bonding strength islarge. Corner reinforcement points have a limited effect in improving jointstrength. There is a new way to arouse great interest in the industry, called"non-flowing underfill". This method is fully compatible with thepcba processing technology and works best to improve the reliability of thefinished product.
3.Improvingpackaging
Thisapproach reduces the impact on the solder joint by providing a certain mat inthe package of the portable product. Design changes include the replacement ofhard shell materials with rubber or more foamy materials. The disadvantage isthat it increases the size and cost of the device.
ShenzhenBaiqiancheng Electronic Co. Ltd, the old electronic processing factory, canprovide you with high-quality SMT processing services, as well as a wealth ofPCBA processing experience.
BQCcan also undertake DIP plug-in processing, hand soldering, testing, finishedgoods assemble as well.