IEC 60068-2-69-2019 pdf download.Environmental testing — Part 2-69: Tests — Test TeITc: Solderability testing of electronic components and printed boards by the wetting balance (force measurement) method
Essais d’environnement — Partle 2-69: Essais — Essai TeITc: Essai de brasabilité des composants
électroniques et cartes imprimées par Ia méthode de Ia balance de mouillage (mesure de Ia force).
B.4.1 General
Surface mounted devices generally have short terminations and so it is advisable to use shallow immersion depths to leave the largest area available above the solder, to develop the largest possible wetting force. The buoyancy forces under these conditions will be relatively small
However, this should be balanced against the thermal needs of the component. The use of very shallow immersion depths may give poor or unpredictable heat transfer into the component, giving variable times before the onset of wetting. Too high immersion depths will give poor wetting force readings. Table 5 and Figure 3 give a list of recommended immersion depths for a range of common components, for the solder bath method, and Table 7, Figure 4 and Annex C give the recommended immersion depths for the solder globule wetting balance method.
As a general guide, where a termination can be presented as a straight vertical face, this will provide the best results. However, it is also necessary to ensure that solder can flow along the face that will eventually be soldered to the printed board, The solder shall also be brought into contact with the solderable coating, avoiding contact with unsolderable material, including exposed cut ends. The immersion angle shall also allow sufficient thermal contact to provide adequate heat transfer into the component.
These requirements will have a different consequence for dipping orientation and dipping depth, for different components.
B.4.2 Resistors and capacitors
Large capacitors can be immersed into the solder with the terminations horizontal, but resistors will generally give better results when one termination is tested vertically, or at an angle between 20° and 45°. Small size capacitors. 1608M (0603) and smaller, may also give better results when dipped with the terminations vertical, or at an angle between 20° and 45°. The smaller pellet size is preferred for 1005M (0402) and 1608M (0603) sizes. it is also recommended that these components be immersed generally to one side of the globule as shown in diagram 2B of Table 7 and Figure 4.
NOTE Components names in parentheses, dimensions are expressed in Imperial.
B.4.3 Small-leaded components
SOT 89, SOT 23 and SOT 223 devices may be dipped at 45°, as the ends of the terminations are Cut in the manufacturing process exposing the bare metal which is generally nonsolderable by conventional test fluxes. By using a dipping angle of 450 the molten solder is brought into contact with the solderable part of the termination, allowing the solder to advance over the termination before the contact angle decreases to zero.
These components are heated to such an extent during the test that adjacent leads are reflowed, Thus, only one lead may be tested on a device. In general, greater sensitivity is obtained by using the smaller solder globule to test these components.
B.4.4 Multi-leaded devices
A complete row of leads on a multi-leaded device can be tested using the solder bath. Greater discrimination may be obtained by removing alternate leads or alternate pairs of leads to reduce the effect of capillary action between the leads, or individual leads may be carefully cut from the component.
The solder globule wetting balance method can be used to test individual leads on a multileaded device, but may also require leads to be removed to prevent solder making contact with two leads or with the solder residue remaining on the previously tested lead.
A complete row of leads on a multi-leaded device may be tested using a single solder globule, but components with a high thermal mass may show variable times for the onset of wetting, because of the differing preheat times and temperatures.
SOIC, VSO and QFP devices may require dipping at an angle of 450, since these devices have cut ends which are non-wettable by conventional test fluxes. Only by using a shallow dipping angle can the solderable surface be brought into contact with the solder. This problem is common to a large number of devices.
PLCC devices should be dipped with the body horizontal and require alternate leads to be removed, to avoid the solder spike remainIng on the previously tested lead making contact with the solder globule.IEC 60068-2-69-2019 pdf download.Environmental testing