Package Mounting Methods
6. Mounting process
Mount
Since the thickness of surface mount packages is thin and they are very susceptible to force from above or below, do not
press against them excessively with the suction nozzle (chuck). If the lower dead point for the suction nozzle is set
incorrectly, it may result in problems such as deformation of the leads or cracking of the chip. Even for packages of similar
thickness and height, they may be slightly different depending on the semiconductor manufacturer, etc. Perform settings
while checking the product specifications.
Applying solder to printed circuit board (for reflow soldering)
1) Cream solder and application method
Methods for applying cream solder include screen printing, using dispensers, or using a metal mask. However, along with
the increasing complexity of solder application, the use of a metal mask has become more and more common. Also, when
selecting cream solder, select the appropriate one according to the application method and circuit wiring density (Table 1)
Table 1 Comparison of classifications of cream solder according to granularity and characteristics
Flux inclusion
amount
(wt %)
Supply method
80 to 120, mesh
Screen
150 to 200, mesh
200, mesh
Solder granularity
(mesh)
250 to 325
325 to 400
325 to 400
325 to 400
Solder powder
shape
Spherical,
deformed
Spherical
Spherical
Spherical,
deformed
Spherical,
deformed
Viscosity of cream solder
(Pa⋅s)
Application
General circuits
10 to 15
250 to 450
Miniature circuits
Miniature circuits
12 to 18
100 to 200
General circuits
300 to 500
8 to 13
400 to 600
General circuits
Chip product
attachment
Dispenser
250 to 400
Board thickness:
1 mm or less
Metal mask
Board thickness:
1 mm or greater
150 to 325
200 to 325
Deformed
2) Points to be careful of when using cream solder
(a) Perform suitable preheating (about 150°C for 2 minutes)
(b) Manage the land dimensions, solder resist printing accuracy, etc. (to make sure that the amount of solder used to fix
the terminals in place is uniform; non-uniform solder quantities may cause the position to be shifted slightly.)
(c) Maintain the proper printing thickness for cream solder (normally, 150
µm
to 300
µm)
(d) Do not apply vibrations to the printed circuit board after mounting the semiconductor devices.
(e) Complete the reflow process within 5 to 7 hours (to prevent deterioration of the cream solder.) after applying solder
M
M15