Acceptability for Electronic Assemblies :Soldering Acceptability Requirements

Acceptability for Electronic Assemblies :Soldering Acceptability Requirements


Target-Class1,2,3
.Solder fillet appears generally smooth and exhibits good wetting of the solder to the parts being joined.
.Outline of the parts is easily determined.
.Solder at the part being joined creates a feathered edge.
.Fillet is concave in shape.



p1s1

See pic for examples of soldering anomalies.

Acceptable-Class1,2,3
.There are materials and processes,e.g.,lead free alloys and slow cooling with large mass PCBs, that may produce dull
matte,gray,or grainy appearing solders that are normal for the material or process involved.These solder connections
are acceptable.
.The solder connection wetting angle (solder to component and solder to PCB termination do not exceed 90°(Figure).
.As an exception,the solder connection to a termination may exhibit a wetting angle exceeding 90°(Figure)when it is 

created by the solder contour extending over the edge of the solder able termination area or solder resist.


p1s2


Figures below illustrate acceptable solder connections with various solder alloys and process conditions.

p2s1 p2s2

SnPb Solder; No Clean Process                                     SnAgCu Solder;No Clean Process

p2s3 p2s4

    SnPb Solder;Water Soluble Flux                                 SnAgCu Solder;Water Soluble Flux

p2s5 p2s6

   SnPb Solder; Water Soluble Flux                                 SnAgCu Solder;Water Soluble Flux

p3s1 p3s2

     SnAgCu Solder;No Clean Process,N2 Reflow                 SnAgCu Solder,No Clean Process;Air Reflow

p3s3 p3s4

      SnPb Solder;No Clean Process                                  SnAgCu Solder;No Clean Process

p3s5 p3s6

     SnPb Solder;No Clean Process                                   SnAgCu Solder;No Clean Process

p4s1 p4s2

                        SnPb Solder                                                      SnAgCu Solder

p4s3 p4s4

                     SnPb Solder                                                           SnAgCu Solder

p4s5 p4s6

         SnPb Solder ; OSP Finish                                                       SnAgCu Solder; OSP Finish

p5s1 p5s2

                     SnAg CuSolder                                                      SnAg CuSolder

p5s3 p5s4

                 SnAgCu  Solder                                                         SnAgCu Solder


       Soldering Anomalies-Exposed Basis Metal

Exposed basis metal on component leads,conductors or land surfaces from nicks,scratches,or other conditions cannot exceed
there quirements of 7.1.2.3 for leads and 10.2.9.1 for conductors and      lands.
Component leads,sides of land patterns,conductors,and use of liquid photo image able solder resist,can have exposed basis
metal per original designs.
Some printed circuit board and conductor finishes have different wetting characteristics and may exhibit solder wetting only to
specific areas. Exposed basis metal or surface finishes should be considered normal under these circumstances,provided the
achieved wetting characteristics of the solder connection areas are acceptable.



Acceptable-Class 1,2,3
.Exposed basis metal on:
.Vertical conductor edges.
.Cut ends of component leads or wires.
.Organic Solderability Preservative (OSP) coated lands.
.Exposed surface finishes that are not part of the required solder fillet  area.

p6s1 p7s1


Acceptable-Class 1

Process Indicator-Class 2,3

.Exposed basis metal on component leads,conductors or land surfaces from nicks or scratches provided conditions

do not exceed the requirements of7.1.2.3 for leads and 10.2.9.1 for conductors and lands.

p7s2


 Soldering Anomalies-Pin Holes/Blow Holes


Acceptable-Class1
ProcessIndicator-Class2,3

.Blowholes (Figures 1,2),pinholes (Figure 3),voids (Figures 4,5),etc.,providing the solder connection meets all other requirements.



p8s1 p8s2                           

                          1                                                                                2                                                                        

p8s3 p8s4

                             3                                                                                 4

 p8s5                     

                                  5

Defect-Class 2,3

Solder connections where pin holes,blowholes,voids,etc.
reduce the connections below minimum requirements(not shown).


Soldering Anomalies-Reflow of Solder Paste

 Defect-Class1,2,3
.Incomplete reflow of solder paste.


p9s1

 p9s2


Soldering Anomalies-Nonwetting

IPC-T-50 defines nonwetting as the inability of molten solder to form a metallic bond with the basis metal.In this Standard,that
includes surface finishes.

Defect-Class 1,2,3
.Solder has not wetted to the land or termination where solder is required.
.Solder coverage does not meet requirements for this termination type.

p10s1

p10s2

p10s3

p10s4

p10s5


Soldering Anomalies-Dewetting

Defect-Class 1,2,3
.Evidence of dewetting that causes the solder connection to not meet the SMT and thru-hole solder fillet requirements.



p11s1

p11s2

p11s3


                          Soldering Anomalies-Excess Solder-Solder Balls/Solder Fines

Solder balls are spheres of solder that remain after the soldering process.Solder fines are typically small balls of the original 

solder paste metal screen size that have splattered around the connection during there flow process.


Target-Class 1,2, 3
.No evidence of solder balls on the printed wiring assembly.

p12s1

Acceptable-Class 1,2,3
.Solder balls are entrapped/encapsulated and do not violate minimum electrical clearance.
 Note:Entrapped/encapsulated/attached is intended to mean that normal service environment of the product will not cause a solder ball to become dislodged.

p12s2


Defect- Class 1,2,3
.Solder balls violate minimum electrical clearance.
.Solder balls are not entrapped in no-clean residue or encapsulated with conformal coating,

or not attached(soldered)to a metal surface.

p13s1

p13s2

p13s3

p13s4


Soldering Anomalies-Excess Solder-Bridging


Defect-Class 1,2,3
.A solder connection across conductors that should not be joined.
.Solder has bridged to adjacent noncommon conductoror component.

p14s1

p14s2

p14s3

p14s4


Soldering Anomalies-Excess Solder-Solder Webbing/Splashes

Defect-Class 1,2,3
.Solder splashes/webbing.


p15s1

p15s2


Soldering Anomalies-Disturbed Solder

Surface appearance with cooling lines as shown in Acceptable pic is more likely to occur in lead free alloys and is not a disturbed solder condition.

p16s1


Defect-Class 1,2,3
Characterized by stress lines from movement in the connection (SnPb alloy).

p16s2

p16s3

p16s4

p16s5


Soldering Anomalies-Fractured Solder


Defect-Class 1,2,3
Fractured or cracked solder.


p17s1

p17s2


Soldering Anomalies-Solder Projections

Defect-Class 1,2,3
.Solder projection,figure 1,violates assembly maximum
height requirements or lead protrusion requirements.
.Projection,figure 2,violates minimum electrical clearance(1).


p18s1 p18s2

                       1                                                              2


p18s3


Soldering Anomalies-Lead Free Fillet Lift

Acceptable-Class 1,2.3
.Fillet lifting-separation of the bottom of the solder and the
top of the land(primary side of plated-through hold connection).

Process Indicator-Class 2
Defect-Class3

.Fillet lifting-separation of the bottom of the solder and the top of the land(secondary side of plated-through hold connection)(not shown).
Defect-Class 1,2,3
.Fillet lifting damages the land attachment.

p19s1


Soldering Anomalies-Hot Tear/Shrink Hole

Acceptable-Class1,2,3
.For connections made with lead free alloys:
.The bottom of the tear is visible.
.The tear or shrink hole does not contact the lead,land or
barrel wall.


Defect-Class 1,2,3
.Shrink holes or hot tear in connections made with SnPb  
solder alloys:

.For connections made with lead free alloys:
.The bottom of the shrink hole or hot tear is not visible.
.The tear or shrink hole contacts the lead or land.

p20s1

                                   end